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

       dladdr, dladdr1 - translate address to symbolic information

       #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.

       The  function dladdr() determines whether the address specified in addr
       is located in one of the shared objects loaded by the calling  applica-
       tion.   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  infor-
       mation  via  the argument extra_info.  The information returned depends
       on the value specified in flags, which can have one  of  the  following

              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 */

              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

       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).

       dladdr() is present in glibc 2.0 and later.  dladdr1()  first  appeared
       in glibc 2.3.3.

       For   an   explanation   of   the  terms  used  in  this  section,  see

       |Interface           | Attribute     | Value   |
       |dladdr(), dladdr1() | Thread safety | MT-Safe |
       These functions are nonstandard GNU extensions that are also present on

       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 com-
       pile time, but merely point to the plt (Procedure Linkage  Table)  sec-
       tion 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)

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Linux                             2017-09-15                         DLADDR(3)
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