NAME

dladdr — find the shared object containing a given address

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <dlfcn.h>

int
dladdr(const void *addr, Dl_info *info);

DESCRIPTION

The dladdr() function queries the dynamic linker for information about the shared object containing the address addr. The information is returned in the structure specified by info. The structure contains at least the following members:

const char *dli_fname

The pathname of the shared object containing the address.

void *dli_fbase

The base address at which the shared object is mapped into the address space of the calling process.

const char *dli_sname

The name of the nearest run-time symbol with a value less than or equal to addr. When possible, the symbol name is returned as it would appear in C source code.

If no symbol with a suitable value is found, both this field and dli_saddr are set to NULL.

void *dli_saddr

The value of the symbol returned in dli_sname.

The dladdr() function is available only in dynamically linked programs.

ERRORS

If a mapped shared object containing addr cannot be found, dladdr() returns 0. In that case, a message detailing the failure can be retrieved by calling dlerror().

On success, a non-zero value is returned.

SEE ALSO

rtld(1), dlopen(3)

HISTORY

The dladdr() function first appeared in the Solaris operating system.

BUGS

This implementation is bug-compatible with the Solaris implementation. In particular, the following bugs are present:

• If addr lies in the main executable rather than in a shared library, the pathname returned in dli_fname may not be correct. The pathname is taken directly from argv[0] of the calling process. When executing a program specified by its full pathname, most shells set argv[0] to the pathname. But this is not required of shells or guaranteed by the operating system.
• If addr is of the form &func, where func is a global function, its value may be an unpleasant surprise. In dynamically linked programs, the address of a global function is considered to point to its program linkage table entry, rather than to the entry point of the function itself. This causes most global functions to appear to be defined within the main executable, rather than in the shared libraries where the actual code resides.
• Returning 0 as an indication of failure goes against long-standing Unix tradition.