DLADDR(3C) Standard C Library Functions DLADDR(3C)

NAME

dladdr, dladdr1 - translate address to symbolic information

SYNOPSIS

#include <dlfcn.h>

int dladdr(void *address, Dl_info_t *dlip);


int dladdr1(void *address, Dl_info_t *dlip, void **info, int flags);

DESCRIPTION

The dladdr() and dladdr1() functions determine if the specified
address is located within one of the mapped objects that make up the
current applications address space. An address is deemed to fall
within a mapped object when it is between the base address, and the
_end address of that object. See NOTES. If a mapped object fits this
criteria, the symbol table made available to the runtime linker is
searched to locate the nearest symbol to the specified address. The
nearest symbol is one that has a value less than or equal to the
required address.


The Dl_info_t structure must be preallocated by the user. The
structure members are filled in by dladdr(), based on the specified
address. The Dl_info_t structure includes the following members:

const char *dli_fname;
void *dli_fbase;
const char *dli_sname;
void *dli_saddr;


The Dl_info_t members provide the following information.

dli_fname
Contains a pointer to the filename of the containing
object.


dli_fbase
Contains the base address of the containing object.


dli_sname
Contains a pointer to the symbol name that is nearest to
the specified address. This symbol either represents
the exact address that was specified, or is the nearest
symbol with a lower address.


dli_saddr
Contains the actual address of the symbol pointed to by
dli_sname.


The dladdr1() function provides for addition information to be
returned as specified by the flags argument:

RTLD_DL_SYMENT
Obtain the ELF symbol table entry for the matched
symbol. The info argument points to a symbol
pointer as defined in <sys/elf.h> (Elf32_Sym
**info or Elf64_Sym **info). Most of the
information found in an ELF symbol can only be
properly interpreted by the runtime linker.
However, there are two fields that contain
information useful to the caller of dladdr1(): The
st_size field contains the size of the referenced
item. The st_info field provides symbol type and
binding attributes. See the Linker and Libraries
Guide for more information.


RTLD_DL_LINKMAP
Obtain the Link_map for the matched file. The info
argument points to a Link_map pointer as defined
in <sys/link.h> (Link_map **info).

RETURN VALUES

If the specified address cannot be matched to a mapped object, a 0 is
returned. Otherwise, a non-zero return is made and the associated
Dl_info_t elements are filled.

USAGE

The dladdr() and dladdr1() functions are one of a family of functions
that give the user direct access to the dynamic linking facilities.
These facilities are available to dynamically-linked processes only.
See Linker and Libraries Guide.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | MT-Safe |
+---------------+-----------------+

SEE ALSO

ld(1), dlclose(3C), dldump(3C), dlerror(3C), dlopen(3C), dlsym(3C),
attributes(7)


Linker and Libraries Guide

NOTES

The Dl_info_t pointer elements point to addresses within the mapped
objects. These pointers can become invalid if objects are removed
prior to these elements use. See dlclose(3C).


If no symbol is found to describe the specified address, both the
dli_sname and dli_saddr members are set to 0.


If the address specified exists within a mapped object in the range
between the base address and the address of the first global symbol
in the object, the reserved local symbol _START_ is returned. This
symbol acts as a label representing the start of the mapped object.
As a label, this symbol has no size. The dli_saddr member is set to
the base address of the associated object. The dli_sname member is
set to the symbol name _START_. If the flag argument is set to
RTLD_DL_SYMENT, symbol information for _START_ is returned.


If an object is acting as a filter, care should be taken when
interpreting the address of any symbol obtained using a handle to
this object. For example, using dlsym(3C) to obtain the symbol _end
for this object, results in returning the address of the symbol _end
within the filtee, not the filter. For more information on filters
see the Linker and Libraries Guide.

February 17, 2023 DLADDR(3C)