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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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dladdr(3) Library Functions Manual dladdr(3)
dladdr, dladdr1 - translate address to symbolic information
Dynamic linking library (libdl, -ldl)
#define _GNU_SOURCE
#include <dlfcn.h>
int dladdr(const void *addr, Dl_info *info);
int dladdr1(const void *addr, Dl_info *info, void **extra_info,
int flags);
The function dladdr() determines whether the address specified in
addr is located in one of the shared objects loaded by the
calling application. If it is, then dladdr() returns information
about the shared object and symbol that overlaps addr. This
information is returned in a Dl_info structure:
typedef struct {
const char *dli_fname; /* Pathname of shared object that
contains address */
void *dli_fbase; /* Base address at which shared
object is loaded */
const char *dli_sname; /* Name of symbol whose definition
overlaps addr */
void *dli_saddr; /* Exact address of symbol named
in dli_sname */
} Dl_info;
If no symbol matching addr could be found, then dli_sname and
dli_saddr are set to NULL.
The function dladdr1() is like dladdr(), but returns additional
information via the argument extra_info. The information
returned depends on the value specified in flags, which can have
one of the following values:
RTLD_DL_LINKMAP
Obtain a pointer to the link map for the matched file.
The extra_info argument points to a pointer to a link_map
structure (i.e., struct link_map **), defined in <link.h>
as:
struct link_map {
ElfW(Addr) l_addr; /* Difference between the
address in the ELF file and
the address in memory */
char *l_name; /* Absolute pathname where
object was found */
ElfW(Dyn) *l_ld; /* Dynamic section of the
shared object */
struct link_map *l_next, *l_prev;
/* Chain of loaded objects */
/* Plus additional fields private to the
implementation */
};
RTLD_DL_SYMENT
Obtain a pointer to the ELF symbol table entry of the
matching symbol. The extra_info argument is a pointer to
a symbol pointer: const ElfW(Sym) **. The ElfW() macro
definition turns its argument into the name of an ELF data
type suitable for the hardware architecture. For example,
on a 64-bit platform, ElfW(Sym) yields the data type name
Elf64_Sym, which is defined in <elf.h> as:
typedef struct {
Elf64_Word st_name; /* Symbol name */
unsigned char st_info; /* Symbol type and binding */
unsigned char st_other; /* Symbol visibility */
Elf64_Section st_shndx; /* Section index */
Elf64_Addr st_value; /* Symbol value */
Elf64_Xword st_size; /* Symbol size */
} Elf64_Sym;
The st_name field is an index into the string table.
The st_info field encodes the symbol's type and binding.
The type can be extracted using the macro
ELF64_ST_TYPE(st_info) (or ELF32_ST_TYPE() on 32-bit
platforms), which yields one of the following values:
Value Description
STT_NOTYPE Symbol type is unspecified
STT_OBJECT Symbol is a data object
STT_FUNC Symbol is a code object
STT_SECTION Symbol associated with a section
STT_FILE Symbol's name is filename
STT_COMMON Symbol is a common data object
STT_TLS Symbol is thread-local data object
STT_GNU_IFUNC Symbol is indirect code object
The symbol binding can be extracted from the st_info field
using the macro ELF64_ST_BIND(st_info) (or ELF32_ST_BIND()
on 32-bit platforms), which yields one of the following
values:
Value Description
STB_LOCAL Local symbol
STB_GLOBAL Global symbol
STB_WEAK Weak symbol
STB_GNU_UNIQUE Unique symbol
The st_other field contains the symbol's visibility, which
can be extracted using the macro
ELF64_ST_VISIBILITY(st_info) (or ELF32_ST_VISIBILITY() on
32-bit platforms), which yields one of the following
values:
Value Description
STV_DEFAULT Default symbol visibility rules
STV_INTERNAL Processor-specific hidden class
STV_HIDDEN Symbol unavailable in other modules
STV_PROTECTED Not preemptible, not exported
On success, these functions return a nonzero value. If the
address specified in addr could be matched to a shared object,
but not to a symbol in the shared object, then the
info->dli_sname and info->dli_saddr fields are set to NULL.
If the address specified in addr could not be matched to a shared
object, then these functions return 0. In this case, an error
message is not available via dlerror(3).
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ dladdr(), dladdr1() │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
GNU.
dladdr()
glibc 2.0.
dladdr1()
glibc 2.3.3.
Solaris.
Sometimes, the function pointers you pass to dladdr() may
surprise you. On some architectures (notably i386 and x86-64),
dli_fname and dli_fbase may end up pointing back at the object
from which you called dladdr(), even if the function used as an
argument should come from a dynamically linked library.
The problem is that the function pointer will still be resolved
at compile time, but merely point to the plt (Procedure Linkage
Table) section of the original object (which dispatches the call
after asking the dynamic linker to resolve the symbol). To work
around this, you can try to compile the code to be position-
independent: then, the compiler cannot prepare the pointer at
compile time any more and gcc(1) will generate code that just
loads the final symbol address from the got (Global Offset Table)
at run time before passing it to dladdr().
dl_iterate_phdr(3), dlinfo(3), dlopen(3), dlsym(3), ld.so(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 dladdr(3)
Pages that refer to this page: dlerror(3), dlinfo(3), dl_iterate_phdr(3), dlopen(3), dlsym(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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