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       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
       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:

              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

       │InterfaceAttributeValue   │
       │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
       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),


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