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man:dladdr1

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(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  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
     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:
                lb lb  lb  l.   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:
                lb lb lb l.   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:
                lb  lb  lb  l.  Value     Description STV_DEFAULT    Default
                symbol  visibility  rules  STV_INTERNAL   Processor-specific
                hidden class STV_HIDDEN     Symbol unavailable in other mod-
                ules 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).
     allbox;  lbw19  lb  lb  l  l l.  Interface Attribute Value T{ dladdr(),
     dladdr1() T}   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 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().

SEE ALSO

     dl_iterate_phdr(3), dlinfo(3), dlopen(3), dlsym(3), ld.so(8)

COLOPHON

     This page is part of release 4.16 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/.

Linux 2017-09-15 DLADDR(3)

/data/webs/external/dokuwiki/data/pages/man/dladdr1.txt · Last modified: 2019/05/17 09:32 by 127.0.0.1

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