dl_iterate_phdr

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

NAME
       dl_iterate_phdr - walk through list of shared objects

SYNOPSIS
       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <link.h>

       int dl_iterate_phdr(
                 int (*callback) (struct dl_phdr_info *info,
                                  size_t size, void *data),
                 void *data);

DESCRIPTION
       The  dl_iterate_phdr() function allows an application to inquire at run
       time to find out which shared objects it has loaded, and the  order  in
       which they were loaded.

       The  dl_iterate_phdr()  function  walks through the list of an applica-
       tion's shared objects and calls the function  callback  once  for  each
       object, until either all shared objects have been processed or callback
       returns a nonzero value.

       Each call to callback  receives  three  arguments:  info,  which  is  a
       pointer  to a structure containing information about the shared object;
       size, which is the size of the structure pointed to by info; and  data,
       which  is a copy of whatever value was passed by the calling program as
       the second argument (also named data) in the call to dl_iterate_phdr().

       The info argument is a structure of the following type:

           struct dl_phdr_info {
               ElfW(Addr)        dlpi_addr;  /* Base address of object */
               const char       *dlpi_name;  /* (Null-terminated) name of
                                                object */
               const ElfW(Phdr) *dlpi_phdr;  /* Pointer to array of
                                                ELF program headers
                                                for this object */
               ElfW(Half)        dlpi_phnum; /* # of items in dlpi_phdr */

               /* The following fields were added in glibc 2.4, after the first
                  version of this structure was available.  Check the size
                  argument passed to the dl_iterate_phdr callback to determine
                  whether or not each later member is available.  */

               unsigned long long int dlpi_adds;
                               /* Incremented when a new object may
                                  have been added */
               unsigned long long int dlpi_subs;
                               /* Incremented when an object may
                                  have been removed */
               size_t dlpi_tls_modid;
                               /* If there is a PT_TLS segment, its module
                                  ID as used in TLS relocations, else zero */
               void  *dlpi_tls_data;
                               /* The address of the calling thread's instance
                                  of this module's PT_TLS segment, if it has
                                  one and it has been allocated in the calling
                                  thread, otherwise a null pointer */
           };

       (The ElfW() macro definition turns its argument into the name of an ELF
       data  type  suitable  for the hardware architecture.  For example, on a
       32-bit platform, ElfW(Addr) yields the data type name Elf32_Addr.  Fur-
       ther  information  on  these  types  can  be  found  in the <elf.h> and
       <link.h> header files.)

       The dlpi_addr field indicates the base address  of  the  shared  object
       (i.e.,  the difference between the virtual memory address of the shared
       object and the offset of that object in the  file  from  which  it  was
       loaded).   The  dlpi_name  field is a null-terminated string giving the
       pathname from which the shared object was loaded.

       To understand the meaning of the dlpi_phdr and  dlpi_phnum  fields,  we
       need to be aware that an ELF shared object consists of a number of seg-
       ments, each of which has a corresponding program header describing  the
       segment.   The  dlpi_phdr field is a pointer to an array of the program
       headers for this shared object.  The  dlpi_phnum  field  indicates  the
       size of this array.

       These program headers are structures of the following form:

           typedef struct {
               Elf32_Word  p_type;    /* Segment type */
               Elf32_Off   p_offset;  /* Segment file offset */
               Elf32_Addr  p_vaddr;   /* Segment virtual address */
               Elf32_Addr  p_paddr;   /* Segment physical address */
               Elf32_Word  p_filesz;  /* Segment size in file */
               Elf32_Word  p_memsz;   /* Segment size in memory */
               Elf32_Word  p_flags;   /* Segment flags */
               Elf32_Word  p_align;   /* Segment alignment */
           } Elf32_Phdr;

       Note that we can calculate the location of a particular program header,
       x, in virtual memory using the formula:

           addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr;

       Possible values for p_type include the following (see <elf.h> for  fur-
       ther details):

           #define PT_LOAD         1    /* Loadable program segment */
           #define PT_DYNAMIC      2    /* Dynamic linking information */
           #define PT_INTERP       3    /* Program interpreter */
           #define PT_NOTE         4    /* Auxiliary information */
           #define PT_SHLIB        5    /* Reserved */
           #define PT_PHDR         6    /* Entry for header table itself */
           #define PT_TLS          7    /* Thread-local storage segment */
           #define PT_GNU_EH_FRAME 0x6474e550 /* GCC .eh_frame_hdr segment */
           #define PT_GNU_STACK  0x6474e551 /* Indicates stack executability */
           #define PT_GNU_RELRO  0x6474e552 /* Read-only after relocation */

RETURN VALUE
       The  dl_iterate_phdr()  function returns whatever value was returned by
       the last call to callback.

VERSIONS
       dl_iterate_phdr() has been supported in glibc since version 2.2.4.

ATTRIBUTES
       For  an  explanation  of  the  terms  used   in   this   section,   see
       attributes(7).

       +------------------+---------------+---------+
       |Interface         | Attribute     | Value   |
       +------------------+---------------+---------+
       |dl_iterate_phdr() | Thread safety | MT-Safe |
       +------------------+---------------+---------+

CONFORMING TO
       The dl_iterate_phdr() function is not specified in any standard.  Vari-
       ous other systems provide a version of this function, although  details
       of  the  returned  dl_phdr_info  structure  differ.   On  the  BSDs and
       Solaris,  the  structure  includes  the  fields  dlpi_addr,  dlpi_name,
       dlpi_phdr,  and dlpi_phnum in addition to other implementation-specific
       fields.

NOTES
       Future versions of  the  C  library  may  add  further  fields  to  the
       dl_phdr_info  structure;  in  that  event, the size argument provides a
       mechanism for the callback function to discover whether it  is  running
       on a system with added fields.

       The first object visited by callback is the main program.  For the main
       program, the dlpi_name field will be an empty string.

EXAMPLE
       The following program displays  a  list  of  pathnames  of  the  shared
       objects  it has loaded.  For each shared object, the program lists some
       information (virtual address, size, flags, and type) for  each  of  the
       objects ELF segments.

       The  following  shell  session  demonstrates the output produced by the
       program on an x86-64 system.  The first shared object for which  output
       is displayed (where the name is an empty string) is the main program.

           $ ./a.out
           Name: "" (9 segments)
                0: [      0x400040; memsz:    1f8] flags: 0x5; PT_PHDR
                1: [      0x400238; memsz:     1c] flags: 0x4; PT_INTERP
                2: [      0x400000; memsz:    ac4] flags: 0x5; PT_LOAD
                3: [      0x600e10; memsz:    240] flags: 0x6; PT_LOAD
                4: [      0x600e28; memsz:    1d0] flags: 0x6; PT_DYNAMIC
                5: [      0x400254; memsz:     44] flags: 0x4; PT_NOTE
                6: [      0x400970; memsz:     3c] flags: 0x4; PT_GNU_EH_FRAME
                7: [         (nil); memsz:      0] flags: 0x6; PT_GNU_STACK
                8: [      0x600e10; memsz:    1f0] flags: 0x4; PT_GNU_RELRO
           Name: "linux-vdso.so.1" (4 segments)
                0: [0x7ffc6edd1000; memsz:    e89] flags: 0x5; PT_LOAD
                1: [0x7ffc6edd1360; memsz:    110] flags: 0x4; PT_DYNAMIC
                2: [0x7ffc6edd17b0; memsz:     3c] flags: 0x4; PT_NOTE
                3: [0x7ffc6edd17ec; memsz:     3c] flags: 0x4; PT_GNU_EH_FRAME
           Name: "/lib64/libc.so.6" (10 segments)
                0: [0x7f55712ce040; memsz:    230] flags: 0x5; PT_PHDR
                1: [0x7f557145b980; memsz:     1c] flags: 0x4; PT_INTERP
                2: [0x7f55712ce000; memsz: 1b6a5c] flags: 0x5; PT_LOAD
                3: [0x7f55716857a0; memsz:   9240] flags: 0x6; PT_LOAD
                4: [0x7f5571688b80; memsz:    1f0] flags: 0x6; PT_DYNAMIC
                5: [0x7f55712ce270; memsz:     44] flags: 0x4; PT_NOTE
                6: [0x7f55716857a0; memsz:     78] flags: 0x4; PT_TLS
                7: [0x7f557145b99c; memsz:   544c] flags: 0x4; PT_GNU_EH_FRAME
                8: [0x7f55712ce000; memsz:      0] flags: 0x6; PT_GNU_STACK
                9: [0x7f55716857a0; memsz:   3860] flags: 0x4; PT_GNU_RELRO
           Name: "/lib64/ld-linux-x86-64.so.2" (7 segments)
                0: [0x7f557168f000; memsz:  20828] flags: 0x5; PT_LOAD
                1: [0x7f55718afba0; memsz:   15a8] flags: 0x6; PT_LOAD
                2: [0x7f55718afe10; memsz:    190] flags: 0x6; PT_DYNAMIC
                3: [0x7f557168f1c8; memsz:     24] flags: 0x4; PT_NOTE
                4: [0x7f55716acec4; memsz:    604] flags: 0x4; PT_GNU_EH_FRAME
                5: [0x7f557168f000; memsz:      0] flags: 0x6; PT_GNU_STACK
                6: [0x7f55718afba0; memsz:    460] flags: 0x4; PT_GNU_RELRO

   Program source

       #define _GNU_SOURCE
       #include <link.h>
       #include <stdlib.h>
       #include <stdio.h>

       static int
       callback(struct dl_phdr_info *info, size_t size, void *data)
       {
           char *type;
           int p_type, j;

           printf("Name: \"%s\" (%d segments)\n", info->dlpi_name,
                      info->dlpi_phnum);

           for (j = 0; j < info->dlpi_phnum; j++) {
               p_type = info->dlpi_phdr[j].p_type;
               type =  (p_type == PT_LOAD) ? "PT_LOAD" :
                       (p_type == PT_DYNAMIC) ? "PT_DYNAMIC" :
                       (p_type == PT_INTERP) ? "PT_INTERP" :
                       (p_type == PT_NOTE) ? "PT_NOTE" :
                       (p_type == PT_INTERP) ? "PT_INTERP" :
                       (p_type == PT_PHDR) ? "PT_PHDR" :
                       (p_type == PT_TLS) ? "PT_TLS" :
                       (p_type == PT_GNU_EH_FRAME) ? "PT_GNU_EH_FRAME" :
                       (p_type == PT_GNU_STACK) ? "PT_GNU_STACK" :
                       (p_type == PT_GNU_RELRO) ? "PT_GNU_RELRO" : NULL;

               printf("    %2d: [%14p; memsz:%7lx] flags: 0x%x; ", j,
                       (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr),
                       info->dlpi_phdr[j].p_memsz,
                       info->dlpi_phdr[j].p_flags);
               if (type != NULL)
                   printf("%s\n", type);
               else
                   printf("[other (0x%x)]\n", p_type);
           }

           return 0;
       }

       int
       main(int argc, char *argv[])
       {
           dl_iterate_phdr(callback, NULL);

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       ldd(1), objdump(1), readelf(1), dladdr(3), dlopen(3), elf(5), ld.so(8)

       Executable and Linking Format Specification, available at various loca-
       tions online.

COLOPHON
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       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/.

GNU                               2017-09-15                DL_ITERATE_PHDR(3)
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