dladdr(3C)

NAME

dladdr() — get the symbolic information for an address

SYNOPSIS

cc [flag]... cfile ... -ldl [library]...

#include <dlfcn.h>

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

Multithread Usage

This routine is thread-safe.

DESCRIPTION

dladdr() is one of a family of routines that give the user direct access to the dynamic linking facilities (using the -ldl option on the compiler or ld command line). dladdr() allows a process to obtain information about the symbol that most closely defines a given address. dladdr() determines whether the specified address is located within one of the load modules (executable or shared libraries) that make up the process' address space. An address is deemed to fall within a load module when it is between the base address at which the load module was mapped and the highest virtual address mapped for that load module, inclusive. If a load module fits this criteria, its dynamic symbol table is searched to locate the nearest symbol to the specified address. The nearest symbol is the one whose value is equal to, or closest to but less than the specified address.

dlip is a pointer to a Dl_info structure. The structure must be allocated by the user. The structure members are set by dladdr() if the specified address falls within one of the load modules. The Dl_info structure contains the following members:

struct { 
    const char *dli_fname; 
    void *dli_fbase; 
    const char *dli_sname; 
    void *dli_saddr; 
    size_t dli_size;     /* ELF only */ 
    int dli_bind;        /* ELF only */ 
    int dli_type; 
}; 

The fields of the Dl_info structure contain the following:

dli_fname: Pointer to the filename of the load module containing the address. The contents of this memory location can change between calls to dladdr().
dli_fbase: Handle to the load module. This can be used as the first argument to dlsym().
dli_sname: Pointer to the name of the nearest symbol to the specified address. This symbol either has the same address, or is the nearest symbol with a lower address. The contents of this memory location can change between calls to dladdr().
dli_saddr: Actual address of the nearest symbol. For code symbols, it contains the address of the OPD (Official Plabel Descriptor) for the nearest code symbol.
dli_size: (ELF process only) Size of the nearest symbol as defined in the dynamic symbol table.
dli_bind: (ELF process only) Binding attribute of the nearest symbol as defined in the dynamic symbol table. The values for this are those used for a symbol's binding in the ELF symbol table (see <elf.h>)
dli_type: Type of the nearest symbol. For ELF process, this is the same as the value for type in the dynamic symbol table. The values for this are those used for a symbol's type in the ELF symbol table (see <elf.h>). For SOM process, this can have the value TYPE_DATA or TYPE_PROCEDURE as defined in <dl.h>).

RETURN VALUE

If the specified address does not fall within one of the load modules, 0 is returned; the contents of the Dl_info structure are not modified. Otherwise, a non-zero value is returned and the fields of the Dl_info structure are set.

DIAGNOSTICS

If no symbol is found within the load module containing address whose value is less than or equal to address, the dli_sname, dli_saddr, and dli_size fields are set to 0; the dli_bind field is set to STB_LOCAL, and the dli_type field is set to STT_NOTYPE.

For a.out's, only a subset of externally visible symbols are typically exported: specifically those referenced by the load modules with which the a.out is linked. The exact set of exported symbols for any shared library or the a.out can be controlled using the linker (see ld(1)).

ERRORS

If dladdr() fails, a subsequent call to dlerrno() returns one of the following values:

RTLD_ERR_BAD_DLL: Invalid symbol address in load module.
RTLD_ERR_CANT_APPLY_RELOC: Cannot apply relocation in library.
RTLD_ERR_DLADDR_NOTFOUND: Address not found in any load module.
RTLD_ERR_NO_MEMORY: Out of memory.
RTLD_ERR_SETCANCELSTATE_FAILED: __thread_setcancelstate failed on entry to or exit from dladdr().
RTLD_ERR_SIGENABLE_FAILED: sigenable failed on exit from dladdr().
RTLD_ERR_SIGINHIBIT_FAILED: siginhibit failed on entry to dladdr().

dladdr(3C)

Technical documentation

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