1DLADDR(3)                  Linux Programmer's Manual                 DLADDR(3)
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NAME

6       dladdr, dladdr1 - translate address to symbolic information
7

SYNOPSIS

9       #define _GNU_SOURCE
10       #include <dlfcn.h>
11
12       int dladdr(void *addr, Dl_info *info);
13
14       int dladdr1(void *addr, Dl_info *info, void **extra_info, int flags);
15
16       Link with -ldl.
17

DESCRIPTION

19       The  function dladdr() determines whether the address specified in addr
20       is located in one of the shared objects loaded by the calling  applica‐
21       tion.   If  it  is,  then dladdr() returns information about the shared
22       object and symbol that overlaps addr.  This information is returned  in
23       a Dl_info structure:
24
25           typedef struct {
26               const char *dli_fname;  /* Pathname of shared object that
27                                          contains address */
28               void       *dli_fbase;  /* Base address at which shared
29                                          object is loaded */
30               const char *dli_sname;  /* Name of symbol whose definition
31                                          overlaps addr */
32               void       *dli_saddr;  /* Exact address of symbol named
33                                          in dli_sname */
34           } Dl_info;
35
36       If no symbol matching addr could be found, then dli_sname and dli_saddr
37       are set to NULL.
38
39       The function dladdr1() is like dladdr(), but returns additional  infor‐
40       mation  via  the argument extra_info.  The information returned depends
41       on the value specified in flags, which can have one  of  the  following
42       values:
43
44       RTLD_DL_LINKMAP
45              Obtain  a  pointer  to  the  link map for the matched file.  The
46              extra_info argument points to a pointer to a link_map  structure
47              (i.e., struct link_map **), defined in <link.h> as:
48
49                  struct link_map {
50                      ElfW(Addr) l_addr;  /* Difference between the
51                                             address in the ELF file and
52                                             the address in memory */
53                      char      *l_name;  /* Absolute pathname where
54                                             object was found */
55                      ElfW(Dyn) *l_ld;    /* Dynamic section of the
56                                             shared object */
57                      struct link_map *l_next, *l_prev;
58                                          /* Chain of loaded objects */
59
60                      /* Plus additional fields private to the
61                         implementation */
62                  };
63
64       RTLD_DL_SYMENT
65              Obtain  a  pointer to the ELF symbol table entry of the matching
66              symbol.  The extra_info  argument  is  a  pointer  to  a  symbol
67              pointer:  const ElfW(Sym) **.  The ElfW() macro definition turns
68              its argument into the name of an ELF data type suitable for  the
69              hardware  architecture.   For  example,  on  a  64-bit platform,
70              ElfW(Sym) yields the data type name Elf64_Sym, which is  defined
71              in <elf.h> as:
72
73                  typedef struct  {
74                      Elf64_Word    st_name;     /* Symbol name */
75                      unsigned char st_info;     /* Symbol type and binding */
76                      unsigned char st_other;    /* Symbol visibility */
77                      Elf64_Section st_shndx;    /* Section index */
78                      Elf64_Addr    st_value;    /* Symbol value */
79                      Elf64_Xword   st_size;     /* Symbol size */
80                  } Elf64_Sym;
81
82              The st_name field is an index into the string table.
83
84              The  st_info  field  encodes the symbol's type and binding.  The
85              type can be extracted using the macro ELF64_ST_TYPE(st_info) (or
86              ELF32_ST_TYPE()  on  32-bit  platforms), which yields one of the
87              following values:
88
89                  Value           Description
90                  STT_NOTYPE      Symbol type is unspecified
91                  STT_OBJECT      Symbol is a data object
92                  STT_FUNC        Symbol is a code object
93                  STT_SECTION     Symbol associated with a section
94                  STT_FILE        Symbol's name is file name
95                  STT_COMMON      Symbol is a common data object
96                  STT_TLS         Symbol is thread-local data object
97                  STT_GNU_IFUNC   Symbol is indirect code object
98
99              The symbol binding can be extracted from the st_info field using
100              the  macro  ELF64_ST_BIND(st_info) (or ELF32_ST_BIND() on 32-bit
101              platforms), which yields one of the following values:
102
103                  Value            Description
104                  STB_LOCAL        Local symbol
105                  STB_GLOBAL       Global symbol
106                  STB_WEAK         Weak symbol
107                  STB_GNU_UNIQUE   Unique symbol
108
109              The st_other field contains the symbol's visibility,  which  can
110              be  extracted  using  the macro ELF64_ST_VISIBILITY(st_info) (or
111              ELF32_ST_VISIBILITY() on 32-bit platforms), which yields one  of
112              the following values:
113
114                  Value           Description
115                  STV_DEFAULT     Default symbol visibility rules
116                  STV_INTERNAL    Processor-specific hidden class
117                  STV_HIDDEN      Symbol unavailable in other modules
118                  STV_PROTECTED   Not preemptible, not exported
119

RETURN VALUE

121       On  success,  these  functions  return a nonzero value.  If the address
122       specified in addr could be matched to a shared object,  but  not  to  a
123       symbol   in   the   shared   object,   then   the  info->dli_sname  and
124       info->dli_saddr fields are set to NULL.
125
126       If the address specified in addr could  not  be  matched  to  a  shared
127       object,  then these functions return 0.  In this case, an error message
128       is not available via dlerror(3).
129

VERSIONS

131       dladdr() is present in glibc 2.0 and later.  dladdr1()  first  appeared
132       in glibc 2.3.3.
133

ATTRIBUTES

135       For   an   explanation   of   the  terms  used  in  this  section,  see
136       attributes(7).
137
138       ┌────────────────────┬───────────────┬─────────┐
139Interface           Attribute     Value   
140       ├────────────────────┼───────────────┼─────────┤
141dladdr(), dladdr1() │ Thread safety │ MT-Safe │
142       └────────────────────┴───────────────┴─────────┘

CONFORMING TO

144       These functions are nonstandard GNU extensions that are also present on
145       Solaris.
146

BUGS

148       Sometimes, the function pointers you pass to dladdr() may surprise you.
149       On  some  architectures  (notably  i386  and  x86-64),  dli_fname   and
150       dli_fbase  may end up pointing back at the object from which you called
151       dladdr(), even if the function used as an argument should come  from  a
152       dynamically linked library.
153
154       The problem is that the function pointer will still be resolved at com‐
155       pile time, but merely point to the plt (Procedure Linkage  Table)  sec‐
156       tion of the original object (which dispatches the call after asking the
157       dynamic linker to resolve the symbol).  To work around  this,  you  can
158       try  to compile the code to be position-independent: then, the compiler
159       cannot prepare the pointer at compile time any  more  and  gcc(1)  will
160       generate  code  that  just  loads the final symbol address from the got
161       (Global Offset Table) at run time before passing it to dladdr().
162

SEE ALSO

164       dl_iterate_phdr(3), dlinfo(3), dlopen(3), dlsym(3), ld.so(8)
165

COLOPHON

167       This page is part of release 4.15 of the Linux  man-pages  project.   A
168       description  of  the project, information about reporting bugs, and the
169       latest    version    of    this    page,    can     be     found     at
170       https://www.kernel.org/doc/man-pages/.
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174Linux                             2017-09-15                         DLADDR(3)
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