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DLADDR(3)                                                               Linux Programmer's Manual                                                              DLADDR(3)

NAME
       dladdr, dladdr1 - translate address to symbolic information

SYNOPSIS
       #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);

       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 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

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 ob‐
       ject, 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).

       β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”
       β”‚Interface                                                                                                                             β”‚ Attribute     β”‚ Value   β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚dladdr(), dladdr1()                                                                                                                   β”‚ Thread safety β”‚ MT-Safe β”‚
       β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜

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)

Linux                                                                          2021-03-22                                                                      DLADDR(3)