DLADDR
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
dladdr, dladdr1 - translate address to symbolic information
SYNOPSIS
#define _GNU_SOURCE
#include <dlfcn.h>
int dladdr(void *addr, Dl_info *info);
int dladdr1(void *addr, Dl_info *info, void **extra_info, int flags);
Link with -ldl.
DESCRIPTION
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 file name
|
| 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
|
RETURN VALUE
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).
VERSIONS
dladdr()
is present in glibc 2.0 and later.
dladdr1()
first appeared in glibc 2.3.3.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
dladdr(),
dladdr1()
| Thread safety | MT-Safe
|
CONFORMING TO
These functions are nonstandard GNU extensions
that are also present on Solaris.
BUGS
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().
SEE ALSO
dl_iterate_phdr(3),
dlinfo(3),
dlopen(3),
dlsym(3),
ld.so(8)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- BUGS
-
- SEE ALSO
-
- COLOPHON
-
|
|
- Running on 
-
:
: 