Tribblix: manual page: mmapobj.2

MMAPOBJ(2) System Calls MMAPOBJ(2)

NAME

mmapobj - map a file object in the appropriate manner

SYNOPSIS

#include <sys/mman.h>

int mmapobj(int fd, uint_t flags, mmapobj_result_t *storage,
uint_t *elements, void *arg);

PARAMETERS

fd
The open file descriptor for the file to be mapped.

flags
Indicates that the default behavior of mmapobj() should
be modified accordingly. Available flags are:

MMOBJ_INTERPRET

Interpret the contents of the file descriptor instead
of just mapping it as a single image. This flag can
be used only with ELF and AOUT files.

MMOBJ_PADDING

When mapping in the file descriptor, add an
additional mapping before the lowest mapping and
after the highest mapping. The size of this padding
is at least as large as the amount pointed to by arg.
These mappings will be private to the process, will
not reserve any swap space and will have no
protections. To use this address space, the
protections for it will need to be changed. This
padding request will be ignored for the AOUT format.

storage
A pointer to the mmapobj_result_t array where the mapping
data will be copied out after a successful mapping of fd.

elements
A pointer to the number of mmapobj_result_t elements
pointed to by storage. On return, elements contains the
number of mappings required to fully map the requested
object. If the original value of elements is too small,
E2BIG is returned and elements is modified to contain the
number of mappings necessary.

arg
A pointer to additional information that might be
associated with the specific request. Only the
MMOBJ_PADDING request uses this argument. If
MMOBJ_PADDING is not specified, arg must be NULL.

DESCRIPTION

The mmapobj() function establishes a set of mappings between a
process's address space and a file. By default, mmapobj() maps the
whole file as a single, private, read-only mapping. The
MMOBJ_INTERPRET flag instructs mmapobj() to attempt to interpret the
file and map the file according to the rules for that file format.
The following ELF and AOUT formats are supported:

ET_EXEC and AOUT executables

This format results in one or more mappings whose size, alignment
and protections are as described by the file's program header
information. The address of each mapping is explicitly defined by
the file's program headers.

ET_DYN and AOUT shared objects

This format results in one or more mappings whose size, alignment
and protections are as described by the file's program header
information. The base address of the initial mapping is chosen by
mmapobj(). The addresses of adjacent mappings are based off of
this base address as defined by the file's program headers.

ET_REL and ET_CORE

This format results in a single, read-only mapping that covers
the whole file. The base address of this mapping is chosen by
mmapobj().

The mmapobj() function will not map over any currently used mappings
within the process, except for the case of an ELF ET_EXEC file for
which a previous reservation has been made via /dev/null. The most
common way to make such a reservation would be with an mmap() of
/dev/null.

Mappings created with mmapobj() can be processed individually by
other system calls such as munmap(2).

The mmapobj_result structure contains the following members:

typedef struct mmapobj_result {
caddr_t mr_addr; /* mapping address */
size_t mr_msize; /* mapping size */
size_t mr_fsize; /* file size */
size_t mr_offset; /* offset into file */
uint_t mr_prot; /* the protections provided */
uint_t mr_flags; /* info on the mapping */
} mmapobj_result_t;

The macro MR_GET_TYPE(mr_flags) must be used when looking for the
above flags in the value of mr_flags.

Values for mr_flags include:

MR_PADDING 0x1 /* this mapping represents requested padding */
MR_HDR_ELF 0x2 /* the ELF header is mapped at mr_addr */
MR_HDR_AOU 0x3 /* the AOUT header is mapped at mr_addr */

When MR_PADDING is set, mr_fsize and mr_offset will both be 0.

The mr_fsize member represents the amount of the file that is mapped
into memory with this mapping.

The mr_offset member is the offset into the mapping where valid data
begins.

The mr_msize member represents the size of the memory mapping
starting at mr_addr. This size may include unused data prior to
mr_offset that exists to satisfy the alignment requirements of this
segment. This size may also include any non-file data that are
required to provide NOBITS data (typically .bss). The system reserves
the right to map more than mr_msize bytes of memory but only mr_msize
bytes will be available to the caller of mmapobj().

RETURN VALUES

Upon successful completion, 0 is returned and elements contains the
number of program headers that are mapped for fd. The data describing
these elements are copied to storage such that the first elements
members of the storage array contain valid mapping data.

On failure, -1 is returned and errno is set to indicate the error. No
data is copied to storage.

ERRORS

The mmapobj() function will fail if:

E2BIG
The elements argument was not large enough to hold the
number of loadable segments in fd. The elements
argument will be modified to contain the number of
segments required.

EACCES
The file system containing the fd to be mapped does not
allow execute access, or the file descriptor pointed to
by fd is not open for reading.

EADDRINUSE
The mapping requirements overlap an object that is
already used by the process.

EAGAIN
There is insufficient room to reserve swap space for
the mapping.

The file to be mapped is already locked using advisory
or mandatory record locking. See fcntl(2).

EBADF
The fd argument is not a valid open file descriptor.

EFAULT
The storage, arg, or elements argument points to an
invalid address.

EINVAL
The flags argument contains an invalid flag.

MMOBJ_PADDING was not specified in flags and arg was
non-null.

ENODEV
The fd argument refers to an object for which mmapobj()
is meaningless, such as a terminal.

ENOMEM
Insufficient memory is available to hold the program
headers.

Insufficient memory is available in the address space
to create the mapping.

ENOTSUP
The current user data model does not match the fd to be
interpreted; thus, a 32-bit process that tried to use
mmapobj() to interpret a 64-bit object would return
ENOTSUP.

The fd argument is a file whose type can not be
interpreted and MMOBJ_INTERPRET was specified in flags.

The ELF header contains an unaligned e_phentsize value.

ENOSYS
An unsupported filesystem operation was attempted while
trying to map in the object.

ATTRIBUTES