PROC(5) File Formats and Configurations PROC(5)

NAME

proc - /proc, the process file system

DESCRIPTION

/proc is a file system that provides access to the state of each
process and light-weight process (lwp) in the system. The name of each
entry in the /proc directory is a decimal number corresponding to a
process-ID. These entries are themselves subdirectories. Access to
process state is provided by additional files contained within each
subdirectory; the hierarchy is described more completely below. In
this document, "/proc file" refers to a non-directory file within the
hierarchy rooted at /proc. The owner of each /proc file and
subdirectory is determined by the user-ID of the process.

/proc can be mounted on any mount point, in addition to the standard
/proc mount point, and can be mounted several places at once. Such
additional mounts are allowed in order to facilitate the confinement of
processes to subtrees of the file system via chroot(2) and yet allow
such processes access to commands like ps(1).

Standard system calls are used to access /proc files: open(2),
close(2), read(2), and write(2) (including readv(2), writev(2),
pread(2), and pwrite(2)). Most files describe process state and can
only be opened for reading. ctl and lwpctl (control) files permit
manipulation of process state and can only be opened for writing. as
(address space) files contain the image of the running process and can
be opened for both reading and writing. An open for writing allows
process control; a read-only open allows inspection but not control.
In this document, we refer to the process as open for reading or
writing if any of its associated /proc files is open for reading or
writing.

In general, more than one process can open the same /proc file at the
same time. Exclusive open is an advisory mechanism provided to allow
controlling processes to avoid collisions with each other. A process
can obtain exclusive control of a target process, with respect to other
cooperating processes, if it successfully opens any /proc file in the
target process for writing (the as or ctl files, or the lwpctl file of
any lwp) while specifying O_EXCL in the open(2). Such an open will
fail if the target process is already open for writing (that is, if an
as, ctl, or lwpctl file is already open for writing). There can be any
number of concurrent read-only opens; O_EXCL is ignored on opens for
reading. It is recommended that the first open for writing by a
controlling process use the O_EXCL flag; multiple controlling processes
usually result in chaos.

If a process opens one of its own /proc files for writing, the open
succeeds regardless of O_EXCL and regardless of whether some other
process has the process open for writing. Self-opens do not count when
another process attempts an exclusive open. (A process cannot exclude
a debugger by opening itself for writing and the application of a
debugger cannot prevent a process from opening itself.) All self-opens
for writing are forced to be close-on-exec (see the F_SETFD operation
of fcntl(2)).

Data may be transferred from or to any locations in the address space
of the traced process by applying lseek(2) to position the as file at
the virtual address of interest followed by read(2) or write(2) (or by
using pread(2) or pwrite(2) for the combined operation). The address-
map files /proc/pid/map and /proc/pid/xmap can be read to determine the
accessible areas (mappings) of the address space. I/O transfers may
span contiguous mappings. An I/O request extending into an unmapped
area is truncated at the boundary. A write request beginning at an
unmapped virtual address fails with EIO; a read request beginning at an
unmapped virtual address returns zero (an end-of-file indication).

Information and control operations are provided through additional
files. <procfs.h> contains definitions of data structures and message
formats used with these files. Some of these definitions involve the
use of sets of flags. The set types sigset_t, fltset_t, and sysset_t
correspond, respectively, to signal, fault, and system call
enumerations defined in <sys/signal.h>, <sys/fault.h>, and
<sys/syscall.h>. Each set type is large enough to hold flags for its
own enumeration. Although they are of different sizes, they have a
common structure and can be manipulated by these macros:

prfillset(&set); /* turn on all flags in set */
premptyset(&set); /* turn off all flags in set */
praddset(&set, flag); /* turn on the specified flag */
prdelset(&set, flag); /* turn off the specified flag */
r = prismember(&set, flag); /* != 0 iff flag is turned on */

One of prfillset() or premptyset() must be used to initialize set
before it is used in any other operation. flag must be a member of the
enumeration corresponding to set.

Every process contains at least one light-weight process, or lwp. Each
lwp represents a flow of execution that is independently scheduled by
the operating system. All lwps in a process share its address space as
well as many other attributes. Through the use of lwpctl and ctl files
as described below, it is possible to affect individual lwps in a
process or to affect all of them at once, depending on the operation.

When the process has more than one lwp, a representative lwp is chosen
by the system for certain process status files and control operations.
The representative lwp is a stopped lwp only if all of the process's
lwps are stopped; is stopped on an event of interest only if all of the
lwps are so stopped (excluding PR_SUSPENDED lwps); is in a PR_REQUESTED
stop only if there are no other events of interest to be found; or,
failing everything else, is in a PR_SUSPENDED stop (implying that the
process is deadlocked). See the description of the status file for
definitions of stopped states. See the PCSTOP control operation for
the definition of "event of interest".

The representative lwp remains fixed (it will be chosen again on the
next operation) as long as all of the lwps are stopped on events of
interest or are in a PR_SUSPENDED stop and the PCRUN control operation
is not applied to any of them.

When applied to the process control file, every /proc control operation
that must act on an lwp uses the same algorithm to choose which lwp to
act upon. Together with synchronous stopping (see PCSET), this enables
a debugger to control a multiple-lwp process using only the process-
level status and control files if it so chooses. More fine-grained
control can be achieved using the lwp-specific files.

The system supports two process data models, the traditional 32-bit
data model in which ints, longs and pointers are all 32 bits wide (the
ILP32 data model), and on some platforms the 64-bit data model in which
longs and pointers, but not ints, are 64 bits in width (the LP64 data
model). In the LP64 data model some system data types, notably size_t,
off_t, time_t and dev_t, grow from 32 bits to 64 bits as well.

The /proc interfaces described here are available to both 32-bit and
64-bit controlling processes. However, many operations attempted by a
32-bit controlling process on a 64-bit target process will fail with
EOVERFLOW because the address space range of a 32-bit process cannot
encompass a 64-bit process or because the data in some 64-bit system
data type cannot be compressed to fit into the corresponding 32-bit
type without loss of information. Operations that fail in this
circumstance include reading and writing the address space, reading the
address-map files, and setting the target process's registers. There
is no restriction on operations applied by a 64-bit process to either a
32-bit or a 64-bit target processes.

The format of the contents of any /proc file depends on the data model
of the observer (the controlling process), not on the data model of the
target process. A 64-bit debugger does not have to translate the
information it reads from a /proc file for a 32-bit process from 32-bit
format to 64-bit format. However, it usually has to be aware of the
data model of the target process. The pr_dmodel field of the status
files indicates the target process's data model.

To help deal with system data structures that are read from 32-bit
processes, a 64-bit controlling program can be compiled with the C
preprocessor symbol _SYSCALL32 defined before system header files are
included. This makes explicit 32-bit fixed-width data structures (like
struct stat32) visible to the 64-bit program. See types32.h(3HEAD).

DIRECTORY STRUCTURE

At the top level, the directory /proc contains entries each of which
names an existing process in the system. These entries are themselves
directories. Except where otherwise noted, the files described below
can be opened for reading only. In addition, if a process becomes a
zombie (one that has exited but whose parent has not yet performed a
wait(3C) upon it), most of its associated /proc files disappear from
the hierarchy; subsequent attempts to open them, or to read or write
files opened before the process exited, will elicit the error ENOENT.

Although process state and consequently the contents of /proc files can
change from instant to instant, a single read(2) of a /proc file is
guaranteed to return a sane representation of state; that is, the read
will be atomic with respect to the state of the process. No such
guarantee applies to successive reads applied to a /proc file for a
running process. In addition, atomicity is not guaranteed for I/O
applied to the as (address-space) file for a running process or for a
process whose address space contains memory shared by another running
process.

A number of structure definitions are used to describe the files.
These structures may grow by the addition of elements at the end in
future releases of the system and it is not legitimate for a program to
assume that they will not.

STRUCTURE OF /proc/pid
A given directory /proc/pid contains the following entries. A process
can use the invisible alias /proc/self if it wishes to open one of its
own /proc files (invisible in the sense that the name "self" does not
appear in a directory listing of /proc obtained from ls(1),
getdents(2), or readdir(3C)).

contracts
A directory containing references to the contracts held by the process.
Each entry is a symlink to the contract's directory under
/system/contract. See contract(5).

as
Contains the address-space image of the process; it can be opened for
both reading and writing. lseek(2) is used to position the file at the
virtual address of interest and then the address space can be examined
or changed through read(2) or write(2) (or by using pread(2) or
pwrite(2) for the combined operation).

ctl
A write-only file to which structured messages are written directing
the system to change some aspect of the process's state or control its
behavior in some way. The seek offset is not relevant when writing to
this file. Individual lwps also have associated lwpctl files in the
lwp subdirectories. A control message may be written either to the
process's ctl file or to a specific lwpctl file with operation-specific
effects. The effect of a control message is immediately reflected in
the state of the process visible through appropriate status and
information files. The types of control messages are described in
detail later. See CONTROL MESSAGES.

status
Contains state information about the process and the representative
lwp. The file contains a pstatus structure which contains an embedded
lwpstatus structure for the representative lwp, as follows:

typedef struct pstatus {
int pr_flags; /* flags (see below) */
int pr_nlwp; /* number of active lwps in the process */
int pr_nzomb; /* number of zombie lwps in the process */
pid_tpr_pid; /* process id */
pid_tpr_ppid; /* parent process id */
pid_tpr_pgid; /* process group id */
pid_tpr_sid; /* session id */
id_t pr_aslwpid; /* obsolete */
id_t pr_agentid; /* lwp-id of the agent lwp, if any */
sigset_t pr_sigpend; /* set of process pending signals */
uintptr_t pr_brkbase; /* virtual address of the process heap */
size_t pr_brksize; /* size of the process heap, in bytes */
uintptr_t pr_stkbase; /* virtual address of the process stack */
size_tpr_stksize; /* size of the process stack, in bytes */
timestruc_t pr_utime; /* process user cpu time */
timestruc_t pr_stime; /* process system cpu time */
timestruc_t pr_cutime; /* sum of children's user times */
timestruc_t pr_cstime; /* sum of children's system times */
sigset_t pr_sigtrace; /* set of traced signals */
fltset_t pr_flttrace; /* set of traced faults */
sysset_t pr_sysentry; /* set of system calls traced on entry */
sysset_t pr_sysexit; /* set of system calls traced on exit */
char pr_dmodel; /* data model of the process */
taskid_t pr_taskid; /* task id */
projid_t pr_projid; /* project id */
zoneid_t pr_zoneid; /* zone id */
lwpstatus_t pr_lwp; /* status of the representative lwp */
} pstatus_t;

pr_flags is a bit-mask holding the following process flags. For
convenience, it also contains the lwp flags for the representative lwp,
described later.

PR_ISSYS process is a system process (see PCSTOP).

PR_VFORKP process is the parent of a vforked child (see
PCWATCH).

PR_FORK process has its inherit-on-fork mode set (see PCSET).

PR_RLC process has its run-on-last-close mode set (see
PCSET).

PR_KLC process has its kill-on-last-close mode set (see
PCSET).

PR_ASYNC process has its asynchronous-stop mode set (see
PCSET).

PR_MSACCT Set by default in all processes to indicate that
microstate accounting is enabled. However, this flag
has been deprecated and no longer has any effect.
Microstate accounting may not be disabled; however, it
is still possible to toggle the flag.

PR_MSFORK Set by default in all processes to indicate that
microstate accounting will be enabled for processes
that this parent fork(2)s. However, this flag has
been deprecated and no longer has any effect. It is
possible to toggle this flag; however, it is not
possible to disable microstate accounting.

PR_BPTADJ process has its breakpoint adjustment mode set (see
PCSET).

PR_PTRACE process has its ptrace-compatibility mode set (see
PCSET).

pr_nlwp is the total number of active lwps in the process. pr_nzomb is
the total number of zombie lwps in the process. A zombie lwp is a non-
detached lwp that has terminated but has not been reaped with
thr_join(3C) or pthread_join(3C).

pr_pid, pr_ppi, pr_pgid, and pr_sid are, respectively, the process ID,
the ID of the process's parent, the process's process group ID, and the
process's session ID.

pr_aslwpid is obsolete and is always zero.

pr_agentid is the lwp-ID for the /proc agent lwp (see the PCAGENT
control operation). It is zero if there is no agent lwp in the
process.

pr_sigpend identifies asynchronous signals pending for the process.

pr_brkbase is the virtual address of the process heap and pr_brksize is
its size in bytes. The address formed by the sum of these values is
the process break (see brk(2)). pr_stkbase and pr_stksize are,
respectively, the virtual address of the process stack and its size in
bytes. (Each lwp runs on a separate stack; the distinguishing
characteristic of the process stack is that the operating system will
grow it when necessary.)

pr_utime, pr_stime, pr_cutime, and pr_cstime are, respectively, the
user CPU and system CPU time consumed by the process, and the
cumulative user CPU and system CPU time consumed by the process's
children, in seconds and nanoseconds.

pr_sigtrace and pr_flttrace contain, respectively, the set of signals
and the set of hardware faults that are being traced (see PCSTRACE and
PCSFAULT).

pr_sysentry and pr_sysexit contain, respectively, the sets of system
calls being traced on entry and exit (see PCSENTRY and PCSEXIT).

pr_dmodel indicates the data model of the process. Possible values
are:

PR_MODEL_ILP32 process data model is ILP32.

PR_MODEL_LP64 process data model is LP64.

PR_MODEL_NATIVE process data model is native.

The pr_taskid, pr_projid, and pr_zoneid fields contain respectively,
the numeric IDs of the task, project, and zone in which the process was
running.

The constant PR_MODEL_NATIVE reflects the data model of the controlling
process, that is, its value is PR_MODEL_ILP32 or PR_MODEL_LP64
according to whether the controlling process has been compiled as a
32-bit program or a 64-bit program, respectively.

pr_lwp contains the status information for the representative lwp:

typedef struct lwpstatus {
int pr_flags; /* flags (see below) */
id_t pr_lwpid; /* specific lwp identifier */
short pr_why; /* reason for lwp stop, if stopped */
short pr_what; /* more detailed reason */
short pr_cursig; /* current signal, if any */
siginfo_t pr_info; /* info associated with signal or fault */
sigset_t pr_lwppend; /* set of signals pending to the lwp */
sigset_t pr_lwphold; /* set of signals blocked by the lwp */
struct sigaction pr_action;/* signal action for current signal */
stack_t pr_altstack; /* alternate signal stack info */
uintptr_t pr_oldcontext; /* address of previous ucontext */
short pr_syscall; /* system call number (if in syscall) */
short pr_nsysarg; /* number of arguments to this syscall */
int pr_errno; /* errno for failed syscall */
long pr_sysarg[PRSYSARGS]; /* arguments to this syscall */
long pr_rval1; /* primary syscall return value */
long pr_rval2; /* second syscall return value, if any */
char pr_clname[PRCLSZ]; /* scheduling class name */
timestruc_t pr_tstamp; /* real-time time stamp of stop */
timestruc_t pr_utime; /* lwp user cpu time */
timestruc_t pr_stime; /* lwp system cpu time */
uintptr_t pr_ustack; /* stack boundary data (stack_t) address */
ulong_t pr_instr; /* current instruction */
prgregset_t pr_reg; /* general registers */
prfpregset_t pr_fpreg; /* floating-point registers */
} lwpstatus_t;

pr_flags is a bit-mask holding the following lwp flags. For
convenience, it also contains the process flags, described previously.

PR_STOPPED The lwp is stopped.

PR_ISTOP The lwp is stopped on an event of interest (see
PCSTOP).

PR_DSTOP The lwp has a stop directive in effect (see PCSTOP).

PR_STEP The lwp has a single-step directive in effect (see
PCRUN).

PR_ASLEEP The lwp is in an interruptible sleep within a system
call.

PR_PCINVAL The lwp's current instruction (pr_instr) is
undefined.

PR_DETACH This is a detached lwp (see pthread_create(3C) and
pthread_join(3C)).

PR_DAEMON This is a daemon lwp (see pthread_create(3C)).

PR_ASLWP This flag is obsolete and is never set.

PR_AGENT This is the /proc agent lwp for the process.

pr_lwpid names the specific lwp.

pr_why and pr_what together describe, for a stopped lwp, the reason for
the stop. Possible values of pr_why and the associated pr_what are:

PR_REQUESTED indicates that the stop occurred in response to a
stop directive, normally because PCSTOP was applied
or because another lwp stopped on an event of
interest and the asynchronous-stop flag (see PCSET)
was not set for the process. pr_what is unused in
this case.

PR_SIGNALLED indicates that the lwp stopped on receipt of a
signal (see PCSTRACE); pr_what holds the signal
number that caused the stop (for a newly-stopped
lwp, the same value is in pr_cursig).

PR_FAULTED indicates that the lwp stopped on incurring a
hardware fault (see PCSFAULT); pr_what holds the
fault number that caused the stop.

PR_SYSENTRY

PR_SYSEXIT indicate a stop on entry to or exit from a system
call (see PCSENTRY and PCSEXIT); pr_what holds the
system call number.

PR_JOBCONTROL indicates that the lwp stopped due to the default
action of a job control stop signal (see
sigaction(2)); pr_what holds the stopping signal
number.

PR_SUSPENDED indicates that the lwp stopped due to internal
synchronization of lwps within the process. pr_what
is unused in this case.

pr_cursig names the current signal, that is, the next signal to be
delivered to the lwp, if any. pr_info, when the lwp is in a
PR_SIGNALLED or PR_FAULTED stop, contains additional information
pertinent to the particular signal or fault (see <sys/siginfo.h>).

pr_lwppend identifies any synchronous or directed signals pending for
the lwp. pr_lwphold identifies those signals whose delivery is being
blocked by the lwp (the signal mask).

pr_action contains the signal action information pertaining to the
current signal (see sigaction(2)); it is undefined if pr_cursig is
zero. pr_altstack contains the alternate signal stack information for
the lwp (see sigaltstack(2)).

pr_oldcontext, if not zero, contains the address on the lwp stack of a
ucontext structure describing the previous user-level context (see
ucontext.h(3HEAD)). It is non-zero only if the lwp is executing in the
context of a signal handler.

pr_syscall is the number of the system call, if any, being executed by
the lwp; it is non-zero if and only if the lwp is stopped on
PR_SYSENTRY or PR_SYSEXIT, or is asleep within a system call (PR_ASLEEP
is set). If pr_syscall is non-zero, pr_nsysarg is the number of
arguments to the system call and pr_sysarg contains the actual
arguments.

pr_rval1, pr_rval2, and pr_errno are defined only if the lwp is stopped
on PR_SYSEXIT or if the PR_VFORKP flag is set. If pr_errno is zero,
pr_rval1 and pr_rval2 contain the return values from the system call.
Otherwise, pr_errno contains the error number for the failing system
call (see <sys/errno.h>).

pr_clname contains the name of the lwp's scheduling class.

pr_tstamp, if the lwp is stopped, contains a time stamp marking when
the lwp stopped, in real time seconds and nanoseconds since an
arbitrary time in the past.

pr_utime is the amount of user level CPU time used by this LWP.

pr_stime is the amount of system level CPU time used by this LWP.

pr_ustack is the virtual address of the stack_t that contains the stack
boundaries for this LWP. See getustack(2) and _stack_grow(3C).

pr_instr contains the machine instruction to which the lwp's program
counter refers. The amount of data retrieved from the process is
machine-dependent. On SPARC based machines, it is a 32-bit word. On
x86-based machines, it is a single byte. In general, the size is that
of the machine's smallest instruction. If PR_PCINVAL is set, pr_instr
is undefined; this occurs whenever the lwp is not stopped or when the
program counter refers to an invalid virtual address.

pr_reg is an array holding the contents of a stopped lwp's general
registers.

SPARC On SPARC-based machines, the predefined
constants R_G0 ... R_G7, R_O0 ... R_O7, R_L0
... R_L7, R_I0 ... R_I7, R_PC, R_nPC, and R_Y
can be used as indices to refer to the
corresponding registers; previous register
windows can be read from their overflow
locations on the stack (however, see the
gwindows file in the /proc/pid/lwp/lwpid
subdirectory).

SPARC V8 (32-bit) For SPARC V8 (32-bit) controlling processes, the
predefined constants R_PSR, R_WIM, and R_TBR can
be used as indices to refer to the corresponding
special registers. For SPARC V9 (64-bit)
controlling processes, the predefined constants
R_CCR, R_ASI, and R_FPRS can be used as indices
to refer to the corresponding special registers.

x86 (32-bit) For 32-bit x86 processes, the predefined
constants listed belowcan be used as indices to
refer to the corresponding registers.
SS
UESP
EFL
CS
EIP
ERR
TRAPNO
EAX
ECX
EDX
EBX
ESP
EBP
ESI
EDI
DS
ES
GS

The preceding constants are listed in
<sys/regset.h>.

Note that a 32-bit process can run on an x86
64-bit system, using the constants listed above.

x86 (64-bit) To read the registers of a 32- or a 64-bit
process, a 64-bit x86 process should use the
predefined constants listed below.
REG_GSBASE
REG_FSBASE
REG_DS
REG_ES
REG_GS
REG_FS
REG_SS
REG_RSP
REG_RFL
REG_CS
REG_RIP
REG_ERR
REG_TRAPNO
REG_RAX
REG_RCX
REG_RDX
REG_RBX
REG_RBP
REG_RSI
REG_RDI
REG_R8
REG_R9
REG_R10
REG_R11
REG_R12
REG_R13
REG_R14
REG_R15

The preceding constants are listed in
<sys/regset.h>.

pr_fpreg is a structure holding the contents of the floating-point
registers.

SPARC registers, both general and floating-point, as seen by a 64-bit
controlling process are the V9 versions of the registers, even if the
target process is a 32-bit (V8) process. V8 registers are a subset of
the V9 registers.

If the lwp is not stopped, all register values are undefined.

psinfo
Contains miscellaneous information about the process and the
representative lwp needed by the ps(1) command. psinfo remains
accessible after a process becomes a zombie. The file contains a
psinfo structure which contains an embedded lwpsinfo structure for the
representative lwp, as follows:

typedef struct psinfo {
int pr_flag; /* process flags (DEPRECATED: see below) */
int pr_nlwp; /* number of active lwps in the process */
int pr_nzomb; /* number of zombie lwps in the process */
pid_t pr_pid; /* process id */
pid_t pr_ppid; /* process id of parent */
pid_t pr_pgid; /* process id of process group leader */
pid_t pr_sid; /* session id */
uid_t pr_uid; /* real user id */
uid_t pr_euid; /* effective user id */
gid_t pr_gid; /* real group id */
gid_t pr_egid; /* effective group id */
uintptr_t pr_addr; /* address of process */
size_t pr_size; /* size of process image in Kbytes */
size_t pr_rssize; /* resident set size in Kbytes */
dev_t pr_ttydev; /* controlling tty device (or PRNODEV) */
ushort_t pr_pctcpu; /* % of recent cpu time used by all lwps */
ushort_t pr_pctmem; /* % of system memory used by process */
timestruc_t pr_start; /* process start time, from the epoch */
timestruc_t pr_time; /* cpu time for this process */
timestruc_t pr_ctime; /* cpu time for reaped children */
char pr_fname[PRFNSZ]; /* name of exec'ed file */
char pr_psargs[PRARGSZ]; /* initial characters of arg list */
int pr_wstat; /* if zombie, the wait() status */
int pr_argc; /* initial argument count */
uintptr_t pr_argv; /* address of initial argument vector */
uintptr_t pr_envp; /* address of initial environment vector */
char pr_dmodel; /* data model of the process */
taskid_t pr_taskid; /* task id */
projid_t pr_projid; /* project id */
poolid_t pr_poolid; /* pool id */
zoneid_t pr_zoneid; /* zone id */
ctid_t pr_contract; /* process contract id */
lwpsinfo_t pr_lwp; /* information for representative lwp */
} psinfo_t;

Some of the entries in psinfo, such as pr_addr, refer to internal
kernel data structures and should not be expected to retain their
meanings across different versions of the operating system.

psinfo_t.pr_flag is a deprecated interface that should no longer be
used. Applications currently relying on the SSYS bit in pr_flag should
migrate to checking PR_ISSYS in the pstatus structure's pr_flags field.

pr_pctcpu and pr_pctmem are 16-bit binary fractions in the range 0.0 to
1.0 with the binary point to the right of the high-order bit (1.0 ==
0x8000). pr_pctcpu is the summation over all lwps in the process.

pr_lwp contains the ps(1) information for the representative lwp. If
the process is a zombie, pr_nlwp, pr_nzomb, and pr_lwp.pr_lwpid are
zero and the other fields of pr_lwp are undefined:

typedef struct lwpsinfo {
int pr_flag; /* lwp flags (DEPRECATED: see below) */
id_t pr_lwpid; /* lwp id */
uintptr_t pr_addr; /* internal address of lwp */
uintptr_t pr_wchan; /* wait addr for sleeping lwp */
char pr_stype; /* synchronization event type */
char pr_state; /* numeric lwp state */
char pr_sname; /* printable character for pr_state */
char pr_nice; /* nice for cpu usage */
short pr_syscall; /* system call number (if in syscall) */
char pr_oldpri; /* pre-SVR4, low value is high priority */
char pr_cpu; /* pre-SVR4, cpu usage for scheduling */
int pr_pri; /* priority, high value = high priority */
ushort_t pr_pctcpu; /* % of recent cpu time used by this lwp */
timestruc_t pr_start; /* lwp start time, from the epoch */
timestruc_t pr_time; /* cpu time for this lwp */
char pr_clname[PRCLSZ]; /* scheduling class name */
char pr_name[PRFNSZ]; /* name of system lwp */
processorid_t pr_onpro; /* processor which last ran this lwp */
processorid_t pr_bindpro;/* processor to which lwp is bound */
psetid_t pr_bindpset; /* processor set to which lwp is bound */
lgrp_id_t pr_lgrp; /* home lgroup */
} lwpsinfo_t;

Some of the entries in lwpsinfo, such as pr_addr, pr_wchan, pr_stype,
pr_state, and pr_name, refer to internal kernel data structures and
should not be expected to retain their meanings across different
versions of the operating system.

lwpsinfo_t.pr_flag is a deprecated interface that should no longer be
used.

pr_pctcpu is a 16-bit binary fraction, as described above. It
represents the CPU time used by the specific lwp. On a multi-processor
machine, the maximum value is 1/N, where N is the number of CPUs.

pr_contract is the id of the process contract of which the process is a
member. See contract(5) and process(5).

cred
Contains a description of the credentials associated with the process:

typedef struct prcred {
uid_t pr_euid; /* effective user id */
uid_t pr_ruid; /* real user id */
uid_t pr_suid; /* saved user id (from exec) */
gid_t pr_egid; /* effective group id */
gid_t pr_rgid; /* real group id */
gid_t pr_sgid; /* saved group id (from exec) */
int pr_ngroups; /* number of supplementary groups */
gid_t pr_groups[1]; /* array of supplementary groups */
} prcred_t;

The array of associated supplementary groups in pr_groups
is of variable length; the cred file contains all of the supplementary
groups. pr_ngroups indicates the number of supplementary groups. (See
also the PCSCRED and PCSCREDX control operations.)

priv
Contains a description of the privileges associated with the process:

typedef struct prpriv {
uint32_t pr_nsets; /* number of privilege set */
uint32_t pr_setsize; /* size of privilege set */
uint32_t pr_infosize; /* size of supplementary data */
priv_chunk_t pr_sets[1]; /* array of sets */
} prpriv_t;

The actual dimension of the pr_sets[] field is
pr_sets[pr_nsets][pr_setsize]

which is followed by additional information about the process state
pr_infosize bytes in size.

The full size of the structure can be computed using
PRIV_PRPRIV_SIZE(prpriv_t *).

secflags
This file contains the security-flags of the process. It contains a
description of the security flags associated with the process.

typedef struct prsecflags {
uint32_t pr_version; /* ABI Versioning of this structure */
secflagset_t pr_effective; /* Effective flags */
secflagset_t pr_inherit; /* Inheritable flags */
secflagset_t pr_lower; /* Lower flags */
secflagset_t pr_upper; /* Upper flags */
} prsecflags_t;

The pr_version field is a version number for the structure, currently
PRSECFLAGS_VERSION_1.

sigact
Contains an array of sigaction structures describing the current
dispositions of all signals associated with the traced process (see
sigaction(2)). Signal numbers are displaced by 1 from array indices,
so that the action for signal number n appears in position n-1 of the
array.

auxv
Contains the initial values of the process's aux vector in an array of
auxv_t structures (see <sys/auxv.h>). The values are those that were
passed by the operating system as startup information to the dynamic
linker.

ldt
This file exists only on x86-based machines. It is non-empty only if
the process has established a local descriptor table (LDT). If non-
empty, the file contains the array of currently active LDT entries in
an array of elements of type struct ssd, defined in <sys/sysi86.h>, one
element for each active LDT entry.

map, xmap
Contain information about the virtual address map of the process. The
map file contains an array of prmap structures while the xmap file
contains an array of prxmap structures. Each structure describes a
contiguous virtual address region in the address space of the traced
process:

typedef struct prmap {
uintptr_tpr_vaddr; /* virtual address of mapping */
size_t pr_size; /* size of mapping in bytes */
char pr_mapname[PRMAPSZ]; /* name in /proc/pid/object */
offset_t pr_offset; /* offset into mapped object, if any */
int pr_mflags; /* protection and attribute flags */
int pr_pagesize; /* pagesize for this mapping in bytes */
int pr_shmid; /* SysV shared memory identifier */
} prmap_t;

typedef struct prxmap {
uintptr_t pr_vaddr; /* virtual address of mapping */
size_t pr_size; /* size of mapping in bytes */
char pr_mapname[PRMAPSZ]; /* name in /proc/pid/object */
offset_t pr_offset; /* offset into mapped object, if any */
int pr_mflags; /* protection and attribute flags */
int pr_pagesize; /* pagesize for this mapping in bytes */
int pr_shmid; /* SysV shared memory identifier */
dev_t pr_dev; /* device of mapped object, if any */
uint64_t pr_ino; /* inode of mapped object, if any */
size_t pr_rss; /* pages of resident memory */
size_t pr_anon; /* pages of resident anonymous memory */
size_t pr_locked; /* pages of locked memory */
uint64_t pr_hatpagesize; /* pagesize of mapping */
} prxmap_t;

pr_vaddr is the virtual address of the mapping within the traced
process and pr_size is its size in bytes. pr_mapname, if it does not
contain a null string, contains the name of a file in the object
directory (see below) that can be opened read-only to obtain a file
descriptor for the mapped file associated with the mapping. This
enables a debugger to find object file symbol tables without having to
know the real path names of the executable file and shared libraries of
the process. pr_offset is the 64-bit offset within the mapped file (if
any) to which the virtual address is mapped.

pr_mflags is a bit-mask of protection and attribute flags:

MA_READ mapping is readable by the traced process.

MA_WRITE mapping is writable by the traced process.

MA_EXEC mapping is executable by the traced process.

MA_SHARED mapping changes are shared by the mapped object.

MA_ISM mapping is intimate shared memory (shared MMU
resources)

MAP_NORESERVE
mapping does not have swap space reserved (mapped
with MAP_NORESERVE)

MA_SHM mapping System V shared memory

A contiguous area of the address space having the same underlying
mapped object may appear as multiple mappings due to varying read,
write, and execute attributes. The underlying mapped object does not
change over the range of a single mapping. An I/O operation to a
mapping marked MA_SHARED fails if applied at a virtual address not
corresponding to a valid page in the underlying mapped object. A write
to a MA_SHARED mapping that is not marked MA_WRITE fails. Reads and
writes to private mappings always succeed. Reads and writes to
unmapped addresses fail.

pr_pagesize is the page size for the mapping, currently always the
system pagesize.

pr_shmid is the shared memory identifier, if any, for the mapping. Its
value is -1 if the mapping is not System V shared memory. See
shmget(2).

pr_dev is the device of the mapped object, if any, for the mapping.
Its value is PRNODEV (-1) if the mapping does not have a device.

pr_ino is the inode of the mapped object, if any, for the mapping. Its
contents are only valid if pr_dev is not PRNODEV.

pr_rss is the number of resident pages of memory for the mapping. The
number of resident bytes for the mapping may be determined by
multiplying pr_rss by the page size given by pr_pagesize.

pr_anon is the number of resident anonymous memory pages (pages which
are private to this process) for the mapping.

pr_locked is the number of locked pages for the mapping. Pages which
are locked are always resident in memory.

pr_hatpagesize is the size, in bytes, of the HAT (MMU) translation for
the mapping. pr_hatpagesize may be different than pr_pagesize. The
possible values are hardware architecture specific, and may change over
a mapping's lifetime.

rmap
Contains information about the reserved address ranges of the process.
The file contains an array of prmap structures, as defined above for
the map file. Each structure describes a contiguous virtual address
region in the address space of the traced process that is reserved by
the system in the sense that an mmap(2) system call that does not
specify MAP_FIXED will not use any part of it for the new mapping.
Examples of such reservations include the address ranges reserved for
the process stack and the individual thread stacks of a multi-threaded
process.

cwd
A symbolic link to the process's current working directory. See
chdir(2). A readlink(2) of /proc/pid/cwd yields a null string.
However, it can be opened, listed, and searched as a directory, and can
be the target of chdir(2).

root
A symbolic link to the process's root directory. /proc/pid/root can
differ from the system root directory if the process or one of its
ancestors executed chroot(2) as super user. It has the same semantics
as /proc/pid/cwd.

fd
A directory containing references to the open files of the process.
Each entry is a decimal number corresponding to an open file descriptor
in the process.

If an entry refers to a regular file, it can be opened with normal file
system semantics but, to ensure that the controlling process cannot
gain greater access than the controlled process, with no file access
modes other than its read/write open modes in the controlled process.
If an entry refers to a directory, it can be accessed with the same
semantics as /proc/pid/cwd. An attempt to open any other type of entry
fails with EACCES.

fdinfo
A directory containing information about each of the process's open
files. Each entry is a decimal number corresponding to an open file
descriptor in the process. Each file contains a prfdinfo_t structure
defined as follows:

typedef struct prfdinfo {
int pr_fd; /* file descriptor number */
mode_t pr_mode; /* (see st_mode in stat(2)) */
uint64_t pr_ino; /* inode number */
uint64_t pr_size; /* file size */
int64_t pr_offset; /* current offset of file descriptor */
uid_t pr_uid; /* owner's user id */
gid_t pr_gid; /* owner's group id */
major_t pr_major; /* major number of device containing file */
minor_t pr_minor; /* minor number of device containing file */
major_t pr_rmajor; /* major number (if special file) */
minor_t pr_rminor; /* minor number (if special file) */
int pr_fileflags; /* (see F_GETXFL in fcntl(2)) */
int pr_fdflags; /* (see F_GETFD in fcntl(2)) */
short pr_locktype; /* (see F_GETLK in fcntl(2)) */
pid_t pr_lockpid; /* process holding file lock (see F_GETLK) */
int pr_locksysid; /* sysid of locking process (see F_GETLK) */
pid_t pr_peerpid; /* peer process (socket, door) */
int pr_filler[25]; /* reserved for future use */
char pr_peername[PRFNSZ]; /* peer process name */
#if __STDC_VERSION__ >= 199901L
char pr_misc[]; /* self describing structures */
#else
char pr_misc[1];
#endif
} prfdinfo_t;

The pr_misc element points to a list of additional miscellaneous data
items, each of which has a header of type pr_misc_header_t specifying
the size and type, and some data which immediately follow the header.

typedef struct pr_misc_header {
uint_t pr_misc_size;
uint_t pr_misc_type;
} pr_misc_header_t;

The pr_misc_size field is the sum of the sizes of the header and the
associated data and any trailing padding bytes which will be set to
zero. The end of the list is indicated by a header with a zero size
and a type with all bits set.

The following miscellaneous data types can be present:

PR_PATHNAME The file descriptor's path in the
filesystem. This is a NUL-terminated
sequence of characters.

PR_SOCKETNAME A sockaddr structure representing the
local socket name for this file
descriptor, as would be returned by
calling getsockname() within the
process.

PR_PEERSOCKNAME A sockaddr structure representing the
peer socket name for this file
descriptor, as would be returned by
calling getpeername() within the
process.

PR_SOCKOPTS_BOOL_OPTS An unsigned integer which has bits set
corresponding to options which are set
on the underlying socket. The following
bits may be set:

PR_SO_DEBUG

PR_SO_REUSEADDR

PR_SO_REUSEPORT

PR_SO_KEEPALIVE

PR_SO_DONTROUTE

PR_SO_BROADCAST

PR_SO_OOBINLINE

PR_SO_DGRAM_ERRIND

PR_SO_ALLZONES

PR_SO_MAC_EXEMPT

PR_SO_EXCLBIND

PR_SO_PASSIVE_CONNECT

PR_SO_ACCEPTCONN

PR_UDP_NAT_T_ENDPOINT

PR_SO_VRRP

PR_SO_MAC_IMPLICIT

PR_SOCKOPT_LINGER A struct linger as would be returned by
calling getsockopt(SO_LINGER) within the
process.

PR_SOCKOPT_SNDBUF The data that would be returned by
calling getsockopt(SO_SNDBUF) within the
process.

PR_SOCKOPT_RCVBUF The data that would be returned by
calling getsockopt(SO_RCVBUF) within the
process.

PR_SOCKOPT_IP_NEXTHOP The data that would be returned by
calling getsockopt(IPPROTO_IP,
IP_NEXTHOP) within the process.

PR_SOCKOPT_IPV6_NEXTHOP The data that would be returned by
calling getsockopt(IPPROTO_IPV6,
IPV6_NEXTHOP) within the process.

PR_SOCKOPT_TYPE The data that would be returned by
calling getsockopt(SO_TYPE) within the
process.

PR_SOCKOPT_TCP_CONGESTION For TCP sockets, the data that would be
returned by calling
getsockopt(IPPROTO_TCP, TCP_CONGESTION)
within the process. This is a NUL-
terminated character array containing
the name of the congestion algorithm in
use for the socket.

PR_SOCKFILTERS_PRIV Private data relating to up to the first
32 socket filters pushed on this
descriptor.

object
A directory containing read-only files with names corresponding to the
pr_mapname entries in the map and pagedata files. Opening such a file
yields a file descriptor for the underlying mapped file associated with
an address-space mapping in the process. The file name a.out appears
in the directory as an alias for the process's executable file.

The object directory makes it possible for a controlling process to
gain access to the object file and any shared libraries (and
consequently the symbol tables) without having to know the actual path
names of the executable files.

path
A directory containing symbolic links to files opened by the process.
The directory includes one entry for cwd and root. The directory also
contains a numerical entry for each file descriptor in the fd
directory, and entries matching those in the object directory. If this
information is not available, any attempt to read the contents of the
symbolic link will fail. This is most common for files that do not
exist in the filesystem namespace (such as FIFOs and sockets), but can
also happen for regular files. For the file descriptor entries, the
path may be different from the one used by the process to open the
file.

pagedata
Opening the page data file enables tracking of address space references
and modifications on a per-page basis.

A read(2) of the page data file descriptor returns structured page data
and atomically clears the page data maintained for the file by the
system. That is to say, each read returns data collected since the
last read; the first read returns data collected since the file was
opened. When the call completes, the read buffer contains the
following structure as its header and thereafter contains a number of
section header structures and associated byte arrays that must be
accessed by walking linearly through the buffer.

typedef struct prpageheader {
timestruc_t pr_tstamp; /* real time stamp, time of read() */
ulong_t pr_nmap; /* number of address space mappings */
ulong_t pr_npage; /* total number of pages */
} prpageheader_t;

The header is followed by pr_nmap prasmap structures and associated
data arrays. The prasmap structure contains the following elements:

typedef struct prasmap {
uintptr_t pr_vaddr; /* virtual address of mapping */
ulong_t pr_npage; /* number of pages in mapping */
char pr_mapname[PRMAPSZ]; /* name in /proc/pid/object */
offset_t pr_offset; /* offset into mapped object, if any */
int pr_mflags; /* protection and attribute flags */
int pr_pagesize; /* pagesize for this mapping in bytes */
int pr_shmid; /* SysV shared memory identifier */
} prasmap_t;

Each section header is followed by pr_npage bytes, one byte for each
page in the mapping, plus 0-7 null bytes at the end so that the next
prasmap structure begins on an eight-byte aligned boundary. Each data
byte may contain these flags:

PG_REFERENCED page has been referenced.

PG_MODIFIED page has been modified.

If the read buffer is not large enough to contain all of the page data,
the read fails with E2BIG and the page data is not cleared. The
required size of the read buffer can be determined through fstat(2).
Application of lseek(2) to the page data file descriptor is
ineffective; every read starts from the beginning of the file. Closing
the page data file descriptor terminates the system overhead associated
with collecting the data.

More than one page data file descriptor for the same process can be
opened, up to a system-imposed limit per traced process. A read of one
does not affect the data being collected by the system for the others.
An open of the page data file will fail with ENOMEM if the system-
imposed limit would be exceeded.

watch
Contains an array of prwatch structures, one for each watched area
established by the PCWATCH control operation. See PCWATCH for details.

usage
Contains process usage information described by a prusage structure
which contains at least the following fields:

typedef struct prusage {
id_t pr_lwpid; /* lwp id. 0: process or defunct */
int pr_count; /* number of contributing lwps */
timestruc_t pr_tstamp; /* real time stamp, time of read() */
timestruc_t pr_create; /* process/lwp creation time stamp */
timestruc_t pr_term; /* process/lwp termination time stamp */
timestruc_t pr_rtime; /* total lwp real (elapsed) time */
timestruc_t pr_utime; /* user level CPU time */
timestruc_t pr_stime; /* system call CPU time */
timestruc_t pr_ttime; /* other system trap CPU time */
timestruc_t pr_tftime; /* text page fault sleep time */
timestruc_t pr_dftime; /* data page fault sleep time */
timestruc_t pr_kftime; /* kernel page fault sleep time */
timestruc_t pr_ltime; /* user lock wait sleep time */
timestruc_t pr_slptime; /* all other sleep time */
timestruc_t pr_wtime; /* wait-cpu (latency) time */
timestruc_t pr_stoptime; /* stopped time */
ulong_t pr_minf; /* minor page faults */
ulong_t pr_majf; /* major page faults */
ulong_t pr_nswap; /* swaps */
ulong_t pr_inblk; /* input blocks */
ulong_t pr_oublk; /* output blocks */
ulong_t pr_msnd; /* messages sent */
ulong_t pr_mrcv; /* messages received */
ulong_t pr_sigs; /* signals received */
ulong_t pr_vctx; /* voluntary context switches */
ulong_t pr_ictx; /* involuntary context switches */
ulong_t pr_sysc; /* system calls */
ulong_t pr_ioch; /* chars read and written */
} prusage_t;

Microstate accounting is now continuously enabled. While this
information was previously an estimate, if microstate accounting were
not enabled, the current information is now never an estimate
represents time the process has spent in various states.

lstatus
Contains a prheader structure followed by an array of lwpstatus
structures, one for each active lwp in the process (see also
/proc/pid/lwp/lwpid/lwpstatus, below). The prheader structure
describes the number and size of the array entries that follow.

typedef struct prheader {
long pr_nent; /* number of entries */
size_t pr_entsize; /* size of each entry, in bytes */
} prheader_t;

The lwpstatus structure may grow by the addition of elements at the end
in future releases of the system. Programs must use pr_entsize in the
file header to index through the array. These comments apply to all
/proc files that include a prheader structure (lpsinfo and lusage,
below).

lpsinfo
Contains a prheader structure followed by an array of lwpsinfo
structures, one for eachactive and zombie lwp in the process. See also
/proc/pid/lwp/lwpid/lwpsinfo, below.

lusage
Contains a prheader structure followed by an array of prusage
structures, one for each active lwp in the process, plus an additional
element at the beginning that contains the summation over all defunct
lwps (lwps that once existed but no longer exist in the process).
Excluding the pr_lwpid, pr_tstamp, pr_create, and pr_term entries, the
entry-by-entry summation over all these structures is the definition of
the process usage information obtained from the usage file. (See also
/proc/pid/lwp/lwpid/lwpusage, below.)

lwp
A directory containing entries each of which names an active or zombie
lwp within the process. These entries are themselves directories
containing additional files as described below. Only the lwpsinfo file
exists in the directory of a zombie lwp.

STRUCTURE OF /proc/pid/lwp/lwpid
A given directory /proc/pid/lwp/lwpid contains the following entries:

lwpctl
Write-only control file. The messages written to this file affect the
specific lwp rather than the representative lwp, as is the case for the
process's ctl file.

lwpname
A buffer of THREAD_NAME_MAX bytes representing the LWP name; the buffer
is zero-filled if the thread name is shorter than the buffer. If no
thread name is set, the buffer contains the empty string. A read with
a buffer shorter than THREAD_NAME_MAX bytes is not guaranteed to be
NUL-terminated. Writing to this file will set the LWP name for the
specific lwp. This file may not be present in older operating system
versions. THREAD_NAME_MAX may increase in the future; clients should
be prepared for this.

lwpstatus
lwp-specific state information. This file contains the lwpstatus
structure for the specific lwp as described above for the
representative lwp in the process's status file.

lwpsinfo
lwp-specific ps(1) information. This file contains the lwpsinfo
structure for the specific lwp as described above for the
representative lwp in the process's psinfo file. The lwpsinfo file
remains accessible after an lwp becomes a zombie.

lwpusage
This file contains the prusage structure for the specific lwp as
described above for the process's usage file.

gwindows
This file exists only on SPARC based machines. If it is non-empty, it
contains a gwindows_t structure, defined in <sys/regset.h>, with the
values of those SPARC register windows that could not be stored on the
stack when the lwp stopped. Conditions under which register windows
are not stored on the stack are: the stack pointer refers to
nonexistent process memory or the stack pointer is improperly aligned.
If the lwp is not stopped or if there are no register windows that
could not be stored on the stack, the file is empty (the usual case).

xregs
Extra state registers. The extra state register set is architecture
dependent; this file is empty if the system does not support extra
state registers. If the file is non-empty, it contains an architecture
dependent structure of type prxregset_t, defined in <procfs.h>, with
the values of the lwp's extra state registers. If the lwp is not
stopped, all register values are undefined. See also the PCSXREG
control operation, below. Reading this data currently requires that
the process be stopped.

asrs
This file exists only for 64-bit SPARC V9 processes. It contains an
asrset_t structure, defined in <sys/regset.h>, containing the values of
the lwp's platform-dependent ancillary state registers. If the lwp is
not stopped, all register values are undefined. See also the PCSASRS
control operation, below.

spymaster
For an agent lwp (see PCAGENT), this file contains a psinfo_t structure
that corresponds to the process that created the agent lwp at the time
the agent was created. This structure is identical to that retrieved
via the psinfo file, with one modification: the pr_time field does not
correspond to the CPU time for the process, but rather to the creation
time of the agent lwp.

templates
A directory which contains references to the active templates for the
lwp, named by the contract type. Changes made to an active template
descriptor do not affect the original template which was activated,
though they do affect the active template. It is not possible to
activate an active template descriptor. See contract(5).

ARCHITECTURE-SPECIFIC STRUCTURES
x86
While the x86 prxregset_t structure is opaque to consumers, it is made
up of several different components due to the fact that different x86
processors enumerate different architectural extensions.

The structure begins with a header, the prxregset_hdr_t, which is
followed by a number of different information sections which describe
different possible extended registers. Each of those is covered by a
prxregset_info_t, and then finally there are different data payloads
that represent each extended register.

The number of different informational entries varies from system to
system based on the set of architectural features that the system
supports and the corresponding OS enablement for them. This structure
is built around the idea of the x86 xsave structure. That is, there is
a central header which describes a bit-vector of what extended features
are present and have valid state.

Each x86 xregs file begins with the prxregset_hdr_t which looks like:

typedef struct prxregset_hdr {
uint32_t pr_type;
uint32_t pr_size;
uint32_t pr_flags;
uint32_t pr_pad[4];
uint32_t pr_ninfo;
prxregset_info_t pr_info[];
} prxregset_hdr_t;

The pr_type member is always set to PR_TYPE_XSAVE. This is used to
indicate the type of file that is present. There may be different file
types in the future on x86 so this value should always be checked. If
it is not PR_TYPE_XSAVE then the rest of the structure may look
different. The pr_size member indicates the size in bytes of the
overall structure. The pr_flags and pr_pad values are currently
reserved for future use. They will be set to zero right now when read
and must be set to zero when writing the data. The pr_ninfo member
indicates the number of informational items are present in pr_info.
There will be one informational item for each register set that exists.

The pr_info member points to an array of informational members. These
immediately follow the structure, though the pr_info member may not be
available directly if not in an environment compatible with some C99
features. Each prxregset_info_t structure looks like:

typedef struct prxregset_info {
uint32_t pri_type;
uint32_t pri_flags;
uint32_t pri_size;
uint32_t pri_offset;
} prxregset_info_t;

The pri_type member is used to indicate the type of data and its format
that this represents. Types are listed below. The pri_flags member is
used to indicate future extensions or information about these items.
Right now, these are all zero. The pri_size member indicates the size
in bytes of the type's data. The pri_offset member indicates the
offset to the start of the data section from the beginning of the xregs
file. That is an offset of 0 would be the first byte of the
prxregset_hdr_t.

The following types of structures and their corresponding data
structures are currently defined:

PRX_INFO_XCR - prxregset_xcr_t
This structure provides read-only access to understanding the
CPU's settings for this thread. In particular, it lets you see
what is set in the x86 %xcr0 register which is the extended
feature control register and controls what extended features
the CPU actually uses. It also contains the x86 extended
feature disable MSR which controls features that are ignored.
The prxregset_xcr_t looks like:

typedef struct prxregset_xcr {
uint64_t prx_xcr_xcr0;
uint64_t prx_xcr_xfd;
uint64_t prx_xcr_pad[2];
} prxregset_xcr_t;

When setting the xregs, this entry can be left out. If it is
included, it must match the existing entries, otherwise an
error will be generated.

PRX_INFO_XSAVE - prxregset_xsave_t
This structure represents the same as the actual Intel xsave
structure, which has both the traditional XMM state that comes
from the fxsave instruction and then also contains the xsave
header itself. The structure varies between 32-bit and 64-bit
applications. The structure itself looks like:

typedef struct prxregset_xsave {
uint16_t prx_fx_fcw;
uint16_t prx_fx_fsw;
uint16_t prx_fx_fctw; /* compressed tag word */
uint16_t prx_fx_fop;
#if defined(__amd64)
uint64_t prx_fx_rip;
uint64_t prx_fx_rdp;
#else
uint32_t prx_fx_eip;
uint16_t prx_fx_cs;
uint16_t __prx_fx_ign0;
uint32_t prx_fx_dp;
uint16_t prx_fx_ds;
uint16_t __prx_fx_ign1;
#endif
uint32_t prx_fx_mxcsr;
uint32_t prx_fx_mxcsr_mask;
union {
uint16_t prx_fpr_16[5]; /* 80-bits of x87 state */
u_longlong_t prx_fpr_mmx; /* 64-bit mmx register */
uint32_t _prx__fpr_pad[4]; /* (pad out to 128-bits) */
} fx_st[8];
#if defined(__amd64)
upad128_t prx_fx_xmm[16]; /* 128-bit registers */
upad128_t __prx_fx_ign2[6];
#else
upad128_t prx_fx_xmm[8]; /* 128-bit registers */
upad128_t __prx_fx_ign2[14];
#endif
uint64_t prx_xsh_xstate_bv;
uint64_t prx_xsh_xcomp_bv;
uint64_t prx_xsh_reserved[6];
} prxregset_xsave_t;

In the classical fxsave portion of the structure, most of the
members follow the same meaning and match their presence in the
fpregs file and their use as discussed in the Intel and AMD
software developer manuals. The one exception is that when
setting the prx_fx_mxcsr member reserved bits that are set will
be masked off and ignored.

The most notable fields to consider here right now are the last
few members which are part of the xsave header itself. In
particular, the prx_xsh_xstate_bv component is used to track
the actual features whose content are valid. When reading the
registers, if a given entry is not valid, the register state
will write out the informational entry in its default state.
When setting the extended registers, this notes which features
will be loaded from their default state (as defined by Intel
and AMD's manuals) and which will be loaded from the
informational entries. If a bit is set in the
prx_xsh_xstate_bv entry, then it must be present as its own
informational entry otherwise a write will fail. If an
informational entry is present in a write, but not set in the
prx_xsh_xstate_bv then its contents will be ignored.

The xregs format currently does not support any compressed
items being specified nor does it specify any, so the
prx_xsh_xcomp_bv member will be always set to zero and it and
the reserved members prx_xsh_reserved must all be left as zero.

PRX_INFO_YMM - prxregset_ymm_t
This structure contains the upper 128-bits of the first 16 %ymm
registers (8 for 32-bit applications). To construct a full
vector register, it must be combined with the prx_fx_xmm member
of the PRX_INFO_XSAVE data. In 32-bit applications, the
reserved registers must be written as zero. The structure
itself looks like:

typedef struct prxregset_ymm {
#if defined(__amd64)
upad128_t prx_ymm[16];
#else
upad128_t prx_ymm[8];
upad128_t prx_rsvd[8];
#endif
} prxregset_ymm_t;

PRX_INFO_OPMASK - prxregset_opmask_t
This structure represents one portion of Intel's AVX-512 state:
the 8 64-bit mask registers, %k0 through %k7. The structure
looks like:

typedef struct prxregset_opmask {
uint64_t prx_opmask[8];
} prxregset_opmask_t;

PRX_INFO_ZMM - prxregset_zmm_t
This structure represents one portion of Intel's AVX-512 state:
the upper 256 bits of the 512-bit %zmm0 through %zmm15
registers. Bits 0-127 are found in the prx_fx_xmm member of
the PRX_INFO_XSAVE data and bits 128-255 are found in the
prx_ymm member of the PRX_INFO_YMM. 32-bit applications only
have access to %zmm0 through %zmm7. This structure looks like:

typedef struct prxregset_zmm {
#if defined(__amd64)
upad256_t prx_zmm[16];
#else
upad256_t prx_zmm[8];
upad256_t prx_rsvd[8];
#endif
} prxregset_zmm_t;

PRX_INFO_HI_ZMM - prxregset_hi_zmm_t
This structure represents the third portion of Intel's AVX-512
state: the additional 16 512-bit registers that are available
to 64-bit applications, but not 32-bit applications. This
represents %zmm16 through %zmm31. This structure looks like:

typedef struct prxregset_hi_zmm {
#if defined(__amd64)
upad512_t prx_hi_zmm[16];
#else
upad512_t prx_rsvd[16];
#endif
} prxregset_hi_zmm_t;

Unlike the other lower %zmm registers of %zmm0 through %zmm15, this contains the
entire 512-bit register in one spot and there is no need to look at other
information items to reconstitute the entire vector.

When setting the extended registers, at least the
PRX_INFO_XSAVE component must be present. None of the
component offsets may overlap with the prxregset_hdr_t or any
of the prxregset_info_t structures. When constructing the
overall payload, it is expected that the various structures
start with their naturally expected alignment, which is most
often 16 bytes (that is the value that the C alignof() keyword
will return). The structures that we use are all multiples of
16 bytes to make this easier. Note, when reading the x86 xregs
file, the kernel will write out these structures with increased
alignment beyond the natural alignment of the structure. The
kernel does this so that the structure's data may be more
easily used directly by x86 instructions that require alignment
such as vmovdqu64.

CONTROL MESSAGES

Process state changes are effected through messages written to a
process's ctl file or to an individual lwp's lwpctl file. All control
messages consist of a long that names the specific operation followed
by additional data containing the operand, if any.

Multiple control messages may be combined in a single write(2) (or
writev(2)) to a control file, but no partial writes are permitted.
That is, each control message, operation code plus operand, if any,
must be presented in its entirety to the write(2) and not in pieces
over several system calls. If a control operation fails, no subsequent
operations contained in the same write(2) are attempted.

Descriptions of the allowable control messages follow. In all cases,
writing a message to a control file for a process or lwp that has
terminated elicits the error ENOENT.

PCSTOP PCDSTOP PCWSTOP PCTWSTOP

When applied to the process control file, PCSTOP directs all lwps to
stop and waits for them to stop, PCDSTOP directs all lwps to stop
without waiting for them to stop, and PCWSTOP simply waits for all lwps
to stop. When applied to an lwp control file, PCSTOP directs the
specific lwp to stop and waits until it has stopped, PCDSTOP directs
the specific lwp to stop without waiting for it to stop, and PCWSTOP
simply waits for the specific lwp to stop. When applied to an lwp
control file, PCSTOP and PCWSTOP complete when the lwp stops on an
event of interest, immediately if already so stopped; when applied to
the process control file, they complete when every lwp has stopped
either on an event of interest or on a PR_SUSPENDED stop.

PCTWSTOP is identical to PCWSTOP except that it enables the operation
to time out, to avoid waiting forever for a process or lwp that may
never stop on an event of interest. PCTWSTOP takes a long operand
specifying a number of milliseconds; the wait will terminate
successfully after the specified number of milliseconds even if the
process or lwp has not stopped; a timeout value of zero makes the
operation identical to PCWSTOP.

An "event of interest" is either a PR_REQUESTED stop or a stop that has
been specified in the process's tracing flags (set by PCSTRACE,
PCSFAULT, PCSENTRY, and PCSEXIT). PR_JOBCONTROL and PR_SUSPENDED stops
are specifically not events of interest. (An lwp may stop twice due to
a stop signal, first showing PR_SIGNALLED if the signal is traced and
again showing PR_JOBCONTROL if the lwp is set running without clearing
the signal.) If PCSTOP or PCDSTOP is applied to an lwp that is
stopped, but not on an event of interest, the stop directive takes
effect when the lwp is restarted by the competing mechanism. At that
time, the lwp enters a PR_REQUESTED stop before executing any user-
level code.

A write of a control message that blocks is interruptible by a signal
so that, for example, an alarm(2) can be set to avoid waiting forever
for a process or lwp that may never stop on an event of interest. If
PCSTOP is interrupted, the lwp stop directives remain in effect even
though the write(2) returns an error. (Use of PCTWSTOP with a non-zero
timeout is recommended over PCWSTOP with an alarm(2).)

A system process (indicated by the PR_ISSYS flag) never executes at
user level, has no user-level address space visible through /proc, and
cannot be stopped. Applying one of these operations to a system
process or any of its lwps elicits the error EBUSY.

PCRUN

Make an lwp runnable again after a stop. This operation takes a long
operand containing zero or more of the following flags:

PRCSIG clears the current signal, if any (see PCCSIG).

PRCFAULT clears the current fault, if any (see PCCFAULT).

PRSTEP directs the lwp to execute a single machine instruction.
On completion of the instruction, a trace trap occurs.
If FLTTRACE is being traced, the lwp stops; otherwise, it
is sent SIGTRAP. If SIGTRAP is being traced and is not
blocked, the lwp stops. When the lwp stops on an event
of interest, the single-step directive is cancelled, even
if the stop occurs before the instruction is executed.
This operation requires hardware and operating system
support and may not be implemented on all processors. It
is implemented on SPARC and x86-based machines.

PRSABORT is meaningful only if the lwp is in a PR_SYSENTRY stop or
is marked PR_ASLEEP; it instructs the lwp to abort
execution of the system call (see PCSENTRY and PCSEXIT).

PRSTOP directs the lwp to stop again as soon as possible after
resuming execution (see PCDSTOP). In particular, if the
lwp is stopped on PR_SIGNALLED or PR_FAULTED, the next
stop will show PR_REQUESTED, no other stop will have
intervened, and the lwp will not have executed any user-
level code.

When applied to an lwp control file, PCRUN clears any outstanding
directed-stop request and makes the specific lwp runnable. The
operation fails with EBUSY if the specific lwp is not stopped on an
event of interest or has not been directed to stop or if the agent lwp
exists and this is not the agent lwp (see PCAGENT).

When applied to the process control file, a representative lwp is
chosen for the operation as described for /proc/pid/status. The
operation fails with EBUSY if the representative lwp is not stopped on
an event of interest or has not been directed to stop or if the agent
lwp exists. If PRSTEP or PRSTOP was requested, the representative lwp
is made runnable and its outstanding directed-stop request is cleared;
otherwise all outstanding directed-stop requests are cleared and, if it
was stopped on an event of interest, the representative lwp is marked
PR_REQUESTED. If, as a consequence, all lwps are in the PR_REQUESTED
or PR_SUSPENDED stop state, all lwps showing PR_REQUESTED are made
runnable.

PCSTRACE

Define a set of signals to be traced in the process. The receipt of
one of these signals by an lwp causes the lwp to stop. The set of
signals is defined using an operand sigset_t contained in the control
message. Receipt of SIGKILL cannot be traced; if specified, it is
silently ignored.

If a signal that is included in an lwp's held signal set (the signal
mask) is sent to the lwp, the signal is not received and does not cause
a stop until it is removed from the held signal set, either by the lwp
itself or by setting the held signal set with PCSHOLD.

PCCSIG

The current signal, if any, is cleared from the specific or
representative lwp.

PCSSIG

The current signal and its associated signal information for the
specific or representative lwp are set according to the contents of the
operand siginfo structure (see <sys/siginfo.h>). If the specified
signal number is zero, the current signal is cleared. The semantics of
this operation are different from those of kill(2) in that the signal
is delivered to the lwp immediately after execution is resumed (even if
it is being blocked) and an additional PR_SIGNALLED stop does not
intervene even if the signal is traced. Setting the current signal to
SIGKILL terminates the process immediately.

PCKILL

If applied to the process control file, a signal is sent to the process
with semantics identical to those of kill(2) If applied to an lwp
control file, a directed signal is sent to the specific lwp. The
signal is named in a long operand contained in the message. Sending
SIGKILL terminates the process immediately.

PCUNKILL

A signal is deleted, that is, it is removed from the set of pending
signals. If applied to the process control file, the signal is deleted
from the process's pending signals. If applied to an lwp control file,
the signal is deleted from the lwp's pending signals. The current
signal (if any) is unaffected. The signal is named in a long operand
in the control message. It is an error (EINVAL) to attempt to delete
SIGKILL.

PCSHOLD

Set the set of held signals for the specific or representative lwp
(signals whose delivery will be blocked if sent to the lwp). The set
of signals is specified with a sigset_t operand. SIGKILL and SIGSTOP
cannot be held; if specified, they are silently ignored.

PCSFAULT

Define a set of hardware faults to be traced in the process. On
incurring one of these faults, an lwp stops. The set is defined via
the operand fltset_t structure. Fault names are defined in
<sys/fault.h> and include the following. Some of these may not occur
on all processors; there may be processor-specific faults in addition
to these.

FLTILL illegal instruction

FLTPRIV privileged instruction

FLTBPT breakpoint trap

FLTTRACE trace trap (single-step)

FLTWATCH watchpoint trap

FLTACCESS memory access fault (bus error)

FLTBOUNDS memory bounds violation

FLTIOVF integer overflow

FLTIZDIV integer zero divide

FLTFPE floating-point exception

FLTSTACK unrecoverable stack fault

FLTPAGE recoverable page fault

When not traced, a fault normally results in the posting of a signal to
the lwp that incurred the fault. If an lwp stops on a fault, the
signal is posted to the lwp when execution is resumed unless the fault
is cleared by PCCFAULT or by the PRCFAULT option of PCRUN. FLTPAGE is
an exception; no signal is posted. The pr_info field in the lwpstatus
structure identifies the signal to be sent and contains machine-
specific information about the fault.

PCCFAULT

The current fault, if any, is cleared; the associated signal will not
be sent to the specific or representative lwp.

PCSENTRY PCSEXIT

These control operations instruct the process's lwps to stop on entry
to or exit from specified system calls. The set of system calls to be
traced is defined via an operand sysset_t structure.

When entry to a system call is being traced, an lwp stops after having
begun the call to the system but before the system call arguments have
been fetched from the lwp. When exit from a system call is being
traced, an lwp stops on completion of the system call just prior to
checking for signals and returning to user level. At this point, all
return values have been stored into the lwp's registers.

If an lwp is stopped on entry to a system call (PR_SYSENTRY) or when
sleeping in an interruptible system call (PR_ASLEEP is set), it may be
instructed to go directly to system call exit by specifying the
PRSABORT flag in a PCRUN control message. Unless exit from the system
call is being traced, the lwp returns to user level showing EINTR.

PCWATCH

Set or clear a watched area in the controlled process from a prwatch
structure operand:

typedef struct prwatch {
uintptr_t pr_vaddr; /* virtual address of watched area */
size_t pr_size; /* size of watched area in bytes */
int pr_wflags; /* watch type flags */
} prwatch_t;

pr_vaddr specifies the virtual address of an area of memory to be
watched in the controlled process. pr_size specifies the size of the
area, in bytes. pr_wflags specifies the type of memory access to be
monitored as a bit-mask of the following flags:

WA_READ read access

WA_WRITE write access

WA_EXEC execution access

WA_TRAPAFTER trap after the instruction completes

If pr_wflags is non-empty, a watched area is established for the
virtual address range specified by pr_vaddr and pr_size. If pr_wflags
is empty, any previously-established watched area starting at the
specified virtual address is cleared; pr_size is ignored.

A watchpoint is triggered when an lwp in the traced process makes a
memory reference that covers at least one byte of a watched area and
the memory reference is as specified in pr_wflags. When an lwp
triggers a watchpoint, it incurs a watchpoint trap. If FLTWATCH is
being traced, the lwp stops; otherwise, it is sent a SIGTRAP signal; if
SIGTRAP is being traced and is not blocked, the lwp stops.

The watchpoint trap occurs before the instruction completes unless
WA_TRAPAFTER was specified, in which case it occurs after the
instruction completes. If it occurs before completion, the memory is
not modified. If it occurs after completion, the memory is modified
(if the access is a write access).

Physical i/o is an exception for watchpoint traps. In this instance,
there is no guarantee that memory before the watched area has already
been modified (or in the case of WA_TRAPAFTER, that the memory
following the watched area has not been modified) when the watchpoint
trap occurs and the lwp stops.

pr_info in the lwpstatus structure contains information pertinent to
the watchpoint trap. In particular, the si_addr field contains the
virtual address of the memory reference that triggered the watchpoint,
and the si_code field contains one of TRAP_RWATCH, TRAP_WWATCH, or
TRAP_XWATCH, indicating read, write, or execute access, respectively.
The si_trapafter field is zero unless WA_TRAPAFTER is in effect for
this watched area; non-zero indicates that the current instruction is
not the instruction that incurred the watchpoint trap. The si_pc field
contains the virtual address of the instruction that incurred the trap.

A watchpoint trap may be triggered while executing a system call that
makes reference to the traced process's memory. The lwp that is
executing the system call incurs the watchpoint trap while still in the
system call. If it stops as a result, the lwpstatus structure contains
the system call number and its arguments. If the lwp does not stop, or
if it is set running again without clearing the signal or fault, the
system call fails with EFAULT. If WA_TRAPAFTER was specified, the
memory reference will have completed and the memory will have been
modified (if the access was a write access) when the watchpoint trap
occurs.

If more than one of WA_READ, WA_WRITE, and WA_EXEC is specified for a
watched area, and a single instruction incurs more than one of the
specified types, only one is reported when the watchpoint trap occurs.
The precedence is WA_EXEC, WA_READ, WA_WRITE (WA_EXEC and WA_READ take
precedence over WA_WRITE), unless WA_TRAPAFTER was specified, in which
case it is WA_WRITE, WA_READ, WA_EXEC (WA_WRITE takes precedence).

PCWATCH fails with EINVAL if an attempt is made to specify overlapping
watched areas or if pr_wflags contains flags other than those specified
above. It fails with ENOMEM if an attempt is made to establish more
watched areas than the system can support (the system can support
thousands).

The child of a vfork(2) borrows the parent's address space. When a
vfork(2) is executed by a traced process, all watched areas established
for the parent are suspended until the child terminates or performs an
exec(2). Any watched areas established independently in the child are
cancelled when the parent resumes after the child's termination or
exec(2). PCWATCH fails with EBUSY if applied to the parent of a
vfork(2) before the child has terminated or performed an exec(2). The
PR_VFORKP flag is set in the pstatus structure for such a parent
process.

Certain accesses of the traced process's address space by the operating
system are immune to watchpoints. The initial construction of a signal
stack frame when a signal is delivered to an lwp will not trigger a
watchpoint trap even if the new frame covers watched areas of the
stack. Once the signal handler is entered, watchpoint traps occur
normally. On SPARC based machines, register window overflow and
underflow will not trigger watchpoint traps, even if the register
window save areas cover watched areas of the stack.

Watched areas are not inherited by child processes, even if the traced
process's inherit-on-fork mode, PR_FORK, is set (see PCSET, below).
All watched areas are cancelled when the traced process performs a
successful exec(2).

PCSET PCUNSET

PCSET sets one or more modes of operation for the traced process.
PCUNSET unsets these modes. The modes to be set or unset are specified
by flags in an operand long in the control message:

PR_FORK (inherit-on-fork): When set, the process's tracing flags
and its inherit-on-fork mode are inherited by the child
of a fork(2), fork1(2), or vfork(2). When unset, child
processes start with all tracing flags cleared.

PR_RLC (run-on-last-close): When set and the last writable
/proc file descriptor referring to the traced process or
any of its lwps is closed, all of the process's tracing
flags and watched areas are cleared, any outstanding
stop directives are canceled, and if any lwps are
stopped on events of interest, they are set running as
though PCRUN had been applied to them. When unset, the
process's tracing flags and watched areas are retained
and lwps are not set running on last close.

PR_KLC (kill-on-last-close): When set and the last writable
/proc file descriptor referring to the traced process or
any of its lwps is closed, the process is terminated
with SIGKILL.

PR_ASYNC (asynchronous-stop): When set, a stop on an event of
interest by one lwp does not directly affect any other
lwp in the process. When unset and an lwp stops on an
event of interest other than PR_REQUESTED, all other
lwps in the process are directed to stop.

PR_MSACCT (microstate accounting): Microstate accounting is now
continuously enabled. This flag is deprecated and no
longer has any effect upon microstate accounting.
Applications may toggle this flag; however, microstate
accounting will remain enabled regardless.

PR_MSFORK (inherit microstate accounting): All processes now
inherit microstate accounting, as it is continuously
enabled. This flag has been deprecated and its use no
longer has any effect upon the behavior of microstate
accounting.

PR_BPTADJ (breakpoint trap pc adjustment): On x86-based machines,
a breakpoint trap leaves the program counter (the EIP)
referring to the breakpointed instruction plus one byte.
When PR_BPTADJ is set, the system will adjust the
program counter back to the location of the breakpointed
instruction when the lwp stops on a breakpoint. This
flag has no effect on SPARC based machines, where
breakpoint traps leave the program counter referring to
the breakpointed instruction.

PR_PTRACE (ptrace-compatibility): When set, a stop on an event of
interest by the traced process is reported to the parent
of the traced process by wait(3C), SIGTRAP is sent to
the traced process when it executes a successful
exec(2), setuid/setgid flags are not honored for execs
performed by the traced process, any exec of an object
file that the traced process cannot read fails, and the
process dies when its parent dies. This mode is
deprecated; it is provided only to allow ptrace(3C) to
be implemented as a library function using /proc.

It is an error (EINVAL) to specify flags other than those described
above or to apply these operations to a system process. The current
modes are reported in the pr_flags field of /proc/pid/status and
/proc/pid/lwp/lwp/lwpstatus.

PCSREG

Set the general registers for the specific or representative lwp
according to the operand prgregset_t structure.

On SPARC based systems, only the condition-code bits of the processor-
status register (R_PSR) of SPARC V8 (32-bit) processes can be modified
by PCSREG. Other privileged registers cannot be modified at all.

On x86-based systems, only certain bits of the flags register (EFL) can
be modified by PCSREG: these include the condition codes, direction-
bit, and overflow-bit.

PCSREG fails with EBUSY if the lwp is not stopped on an event of
interest.

PCSVADDR

Set the address at which execution will resume for the specific or
representative lwp from the operand long. On SPARC based systems, both
%pc and %npc are set, with %npc set to the instruction following the
virtual address. On x86-based systems, only %eip is set. PCSVADDR
fails with EBUSY if the lwp is not stopped on an event of interest.

PCSFPREG

Set the floating-point registers for the specific or representative lwp
according to the operand prfpregset_t structure. An error (EINVAL) is
returned if the system does not support floating-point operations (no
floating-point hardware and the system does not emulate floating-point
machine instructions). PCSFPREG fails with EBUSY if the lwp is not
stopped on an event of interest.

PCSXREG

Set the extra state registers for the specific or representative lwp
according to the architecture-dependent operand prxregset_t structure.
An error (EINVAL) is returned if the system does not support extra
state registers or the register state is invalid. PCSXREG fails with
EBUSY if the lwp is not stopped on an event of interest.

PCSASRS

Set the ancillary state registers for the specific or representative
lwp according to the SPARC V9 platform-dependent operand asrset_t
structure. An error (EINVAL) is returned if either the target process
or the controlling process is not a 64-bit SPARC V9 process. Most of
the ancillary state registers are privileged registers that cannot be
modified. Only those that can be modified are set; all others are
silently ignored. PCSASRS fails with EBUSY if the lwp is not stopped
on an event of interest.

PCAGENT

Create an agent lwp in the controlled process with register values from
the operand prgregset_t structure (see PCSREG, above). The agent lwp
is created in the stopped state showing PR_REQUESTED and with its held
signal set (the signal mask) having all signals except SIGKILL and
SIGSTOP blocked.

The PCAGENT operation fails with EBUSY unless the process is fully
stopped via /proc, that is, unless all of the lwps in the process are
stopped either on events of interest or on PR_SUSPENDED, or are stopped
on PR_JOBCONTROL and have been directed to stop via PCDSTOP. It fails
with EBUSY if an agent lwp already exists. It fails with ENOMEM if
system resources for creating new lwps have been exhausted.

Any PCRUN operation applied to the process control file or to the
control file of an lwp other than the agent lwp fails with EBUSY as
long as the agent lwp exists. The agent lwp must be caused to
terminate by executing the SYS_lwp_exit system call trap before the
process can be restarted.

Once the agent lwp is created, its lwp-ID can be found by reading the
process status file. To facilitate opening the agent lwp's control and
status files, the directory name /proc/pid/lwp/agent is accepted for
lookup operations as an invisible alias for /proc/pid/lwp/lwpid, lwpid
being the lwp-ID of the agent lwp (invisible in the sense that the name
"agent" does not appear in a directory listing of /proc/pid/lwp
obtained from ls(1), getdents(2), or readdir(3C).

The purpose of the agent lwp is to perform operations in the controlled
process on behalf of the controlling process: to gather information not
directly available via /proc files, or in general to make the process
change state in ways not directly available via /proc control
operations. To make use of an agent lwp, the controlling process must
be capable of making it execute system calls (specifically, the
SYS_lwp_exit system call trap). The register values given to the agent
lwp on creation are typically the registers of the representative lwp,
so that the agent lwp can use its stack.

If the controlling process neglects to force the agent lwp to execute
the SYS_lwp_exit system call (due to either logic error or fatal
failure on the part of the controlling process), the agent lwp will
remain in the target process. For purposes of being able to debug
these otherwise rogue agents, information as to the creator of the
agent lwp is reflected in that lwp's spymaster file in /proc. Should
the target process generate a core dump with the agent lwp in place,
this information will be available via the NT_SPYMASTER note in the
core file (see core(5)).

The agent lwp is not allowed to execute any variation of the SYS_fork
or SYS_exec system call traps. Attempts to do so yield ENOTSUP to the
agent lwp.

Symbolic constants for system call trap numbers like SYS_lwp_exit and
SYS_lwp_create can be found in the header file <sys/syscall.h>.

PCREAD PCWRITE

Read or write the target process's address space via a priovec
structure operand:

typedef struct priovec {
void *pio_base; /* buffer in controlling process */
size_t pio_len; /* size of read/write request in bytes */
off_t pio_offset; /* virtual address in target process */
} priovec_t;

These operations have the same effect as pread(2) and pwrite(2),
respectively, of the target process's address space file. The
difference is that more than one PCREAD or PCWRITE control operation
can be written to the control file at once, and they can be
interspersed with other control operations in a single write to the
control file. This is useful, for example, when planting many
breakpoint instructions in the process's address space, or when
stepping over a breakpointed instruction. Unlike pread(2) and
pwrite(2), no provision is made for partial reads or writes; if the
operation cannot be performed completely, it fails with EIO.

PCNICE

The traced process's nice(2) value is incremented by the amount in the
operand long. Only a process with the {PRIV_PROC_PRIOCNTL} privilege
asserted in its effective set can better a process's priority in this
way, but any user may lower the priority. This operation is not
meaningful for all scheduling classes.

PCSCRED

Set the target process credentials to the values contained in the
prcred_t structure operand (see /proc/pid/cred). The effective, real,
and saved user-IDs and group-IDs of the target process are set. The
target process's supplementary groups are not changed; the pr_ngroups
and pr_groups members of the structure operand are ignored. Only the
privileged processes can perform this operation; for all others it
fails with EPERM.

PCSCREDX

Operates like PCSCRED but also sets the supplementary groups; the
length of the data written with this control operation should be
"sizeof (prcred_t) + sizeof (gid_t) * (#groups - 1)".

PCSPRIV

Set the target process privilege to the values contained in the
prpriv_t operand (see /proc/pid/priv). The effective, permitted,
inheritable, and limit sets are all changed. Privilege flags can also
be set. The process is made privilege aware unless it can relinquish
privilege awareness. See privileges(7).

The limit set of the target process cannot be grown. The other
privilege sets must be subsets of the intersection of the effective set
of the calling process with the new limit set of the target process or
subsets of the original values of the sets in the target process.

If any of the above restrictions are not met, EPERM is returned. If
the structure written is improperly formatted, EINVAL is returned.

PROGRAMMING NOTES

For security reasons, except for the psinfo, usage, lpsinfo, lusage,
lwpsinfo, and lwpusage files, which are world-readable, and except for
privileged processes, an open of a /proc file fails unless both the
user-ID and group-ID of the caller match those of the traced process
and the process's object file is readable by the caller. The effective
set of the caller is a superset of both the inheritable and the
permitted set of the target process. The limit set of the caller is a
superset of the limit set of the target process. Except for the world-
readable files just mentioned, files corresponding to setuid and setgid
processes can be opened only by the appropriately privileged process.

A process that is missing the basic privilege {PRIV_PROC_INFO} cannot
see any processes under /proc that it cannot send a signal to.

A process that has {PRIV_PROC_OWNER} asserted in its effective set can
open any file for reading. To manipulate or control a process, the
controlling process must have at least as many privileges in its
effective set as the target process has in its effective, inheritable,
and permitted sets. The limit set of the controlling process must be a
superset of the limit set of the target process. Additional
restrictions apply if any of the uids of the target process are 0. See
privileges(7).

Even if held by a privileged process, an open process or lwp file
descriptor (other than file descriptors for the world-readable files)
becomes invalid if the traced process performs an exec(2) of a
setuid/setgid object file or an object file that the traced process
cannot read. Any operation performed on an invalid file descriptor,
except close(2), fails with EAGAIN. In this situation, if any tracing
flags are set and the process or any lwp file descriptor is open for
writing, the process will have been directed to stop and its run-on-
last-close flag will have been set (see PCSET). This enables a
controlling process (if it has permission) to reopen the /proc files to
get new valid file descriptors, close the invalid file descriptors,
unset the run-on-last-close flag (if desired), and proceed. Just
closing the invalid file descriptors causes the traced process to
resume execution with all tracing flags cleared. Any process not
currently open for writing via /proc, but that has left-over tracing
flags from a previous open, and that executes a setuid/setgid or
unreadable object file, will not be stopped but will have all its
tracing flags cleared.

To wait for one or more of a set of processes or lwps to stop or
terminate, /proc file descriptors (other than those obtained by opening
the cwd or root directories or by opening files in the fd or object
directories) can be used in a poll(2) system call. When requested and
returned, either of the polling events POLLPRI or POLLWRNORM indicates
that the process or lwp stopped on an event of interest. Although they
cannot be requested, the polling events POLLHUP, POLLERR, and POLLNVAL
may be returned. POLLHUP indicates that the process or lwp has
terminated. POLLERR indicates that the file descriptor has become
invalid. POLLNVAL is returned immediately if POLLPRI or POLLWRNORM is
requested on a file descriptor referring to a system process (see
PCSTOP). The requested events may be empty to wait simply for
termination.

FILES

/proc directory (list of processes)
/proc/pid
specific process directory
/proc/self
alias for a process's own directory
/proc/pid/as
address space file
/proc/pid/ctl
process control file
/proc/pid/status
process status
/proc/pid/lstatus
array of lwp status structs
/proc/pid/psinfo
process ps(1) info
/proc/pid/lpsinfo
array of lwp ps(1) info structs
/proc/pid/map
address space map
/proc/pid/xmap
extended address space map
/proc/pid/rmap
reserved address map
/proc/pid/cred
process credentials
/proc/pid/priv
process privileges
/proc/pid/sigact
process signal actions
/proc/pid/auxv
process aux vector
/proc/pid/ldt
process LDT (x86 only)
/proc/pid/usage
process usage
/proc/pid/lusage
array of lwp usage structs
/proc/pid/path
symbolic links to process open files
/proc/pid/pagedata
process page data
/proc/pid/watch
active watchpoints
/proc/pid/cwd
alias for the current working directory
/proc/pid/root
alias for the root directory
/proc/pid/fd
directory (list of open files)
/proc/pid/fd/*
aliases for process's open files
/proc/pid/object
directory (list of mapped files)
/proc/pid/object/a.out
alias for process's executable file
/proc/pid/object/*
aliases for other mapped files
/proc/pid/lwp
directory (list of lwps)
/proc/pid/lwp/lwpid
specific lwp directory
/proc/pid/lwp/agent
alias for the agent lwp directory
/proc/pid/lwp/lwpid/lwpctl
lwp control file
/proc/pid/lwp/lwpid/lwpstatus
lwp status
/proc/pid/lwp/lwpid/lwpsinfo
lwp ps(1) info
/proc/pid/lwp/lwpid/lwpusage
lwp usage
/proc/pid/lwp/lwpid/gwindows
register windows (SPARC only)
/proc/pid/lwp/lwpid/xregs
extra state registers
/proc/pid/lwp/lwpid/asrs
ancillary state registers (SPARC V9 only)
/proc/pid/lwp/lwpid/spymaster
For an agent LWP, the controlling process

DIAGNOSTICS

Errors that can occur in addition to the errors normally associated
with file system access:

E2BIG Data to be returned in a read(2) of the page data file
exceeds the size of the read buffer provided by the
caller.

EACCES An attempt was made to examine a process that ran under
a different uid than the controlling process and
{PRIV_PROC_OWNER} was not asserted in the effective set.

EAGAIN The traced process has performed an exec(2) of a
setuid/setgid object file or of an object file that it
cannot read; all further operations on the process or
lwp file descriptor (except close(2)) elicit this error.

EBUSY PCSTOP, PCDSTOP, PCWSTOP, or PCTWSTOP was applied to a
system process; an exclusive open(2) was attempted on a
/proc file for a process already open for writing;
PCRUN, PCSREG, PCSVADDR, PCSFPREG, or PCSXREG was
applied to a process or lwp not stopped on an event of
interest; an attempt was made to mount /proc when it was
already mounted; PCAGENT was applied to a process that
was not fully stopped or that already had an agent lwp.

EINVAL In general, this means that some invalid argument was
supplied to a system call. A non-exhaustive list of
conditions eliciting this error includes: a control
message operation code is undefined; an out-of-range
signal number was specified with PCSSIG, PCKILL, or
PCUNKILL; SIGKILL was specified with PCUNKILL; PCSFPREG
was applied on a system that does not support floating-
point operations; PCSXREG was applied on a system that
does not support extra state registers.

EINTR A signal was received by the controlling process while
waiting for the traced process or lwp to stop via
PCSTOP, PCWSTOP, or PCTWSTOP.

EIO A write(2) was attempted at an illegal address in the
traced process.

ENOENT The traced process or lwp has terminated after being
opened. The basic privilege {PRIV_PROC_INFO} is not
asserted in the effective set of the calling process and
the calling process cannot send a signal to the target
process.

ENOMEM The system-imposed limit on the number of page data file
descriptors was reached on an open of
/proc/pid/pagedata; an attempt was made with PCWATCH to
establish more watched areas than the system can
support; the PCAGENT operation was issued when the
system was out of resources for creating lwps.

ENOSYS An attempt was made to perform an unsupported operation
(such as creat(2), link(2), or unlink(2)) on an entry in
/proc.

EOVERFLOW A 32-bit controlling process attempted to read or write
the as file or attempted to read the map, rmap, or
pagedata file of a 64-bit target process. A 32-bit
controlling process attempted to apply one of the
control operations PCSREG, PCSXREG, PCSVADDR, PCWATCH,
PCAGENT, PCREAD, PCWRITE to a 64-bit target process.

EPERM The process that issued the PCSCRED or PCSCREDX
operation did not have the {PRIV_PROC_SETID} privilege
asserted in its effective set, or the process that
issued the PCNICE operation did not have the
{PRIV_PROC_PRIOCNTL} in its effective set.

An attempt was made to control a process of which the E,
P, and I privilege sets were not a subset of the
effective set of the controlling process or the limit
set of the controlling process is not a superset of
limit set of the controlled process.

Any of the uids of the target process are 0 or an
attempt was made to change any of the uids to 0 using
PCSCRED and the security policy imposed additional
restrictions. See privileges(7).

SEE ALSO

ls(1), ps(1), alarm(2), brk(2), chdir(2), chroot(2), close(2),
creat(2), dup(2), exec(2), fcntl(2), fork(2), fork1(2), fstat(2),
getdents(2), getustack(2), kill(2), lseek(2), mmap(2), nice(2),
open(2), poll(2), pread(2), pwrite(2), read(2), readlink(2), readv(2),
shmget(2), sigaction(2), sigaltstack(2), vfork(2), write(2), writev(2),
_stack_grow(3C), pthread_create(3C), pthread_join(3C), ptrace(3C),
readdir(3C), thr_create(3C), thr_join(3C), wait(3C), siginfo.h(3HEAD),
signal.h(3HEAD), types32.h(3HEAD), ucontext.h(3HEAD), contract(5),
core(5), process(5), lfcompile(7), privileges(7), security-flags(7),
chroot(8)

NOTES

Descriptions of structures in this document include only interesting
structure elements, not filler and padding fields, and may show
elements out of order for descriptive clarity. The actual structure
definitions are contained in <procfs.h>.

BUGS

Because the old ioctl(2)-based version of /proc is currently supported
for binary compatibility with old applications, the top-level directory
for a process, /proc/pid, is not world-readable, but it is world-
searchable. Thus, anyone can open /proc/pid/psinfo even though ls(1)
applied to /proc/pid will fail for anyone but the owner or an
appropriately privileged process. Support for the old ioctl(2)-based
version of /proc will be dropped in a future release, at which time the
top-level directory for a process will be made world-readable.

On SPARC based machines, the types gregset_t and fpregset_t defined in
<sys/regset.h> are similar to but not the same as the types prgregset_t
and prfpregset_t defined in <procfs.h>.

illumos May 8, 2023 illumos