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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 application'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 dlpi_adds;
                               /* Incremented when a new object may
                                  have been added */
               unsigned long long 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.  Further 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 segments, 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 further 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).

       β”Œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”¬β”€β”€β”€β”€β”€β”€β”€β”€β”€β”
       β”‚Interface                                                                                                                             β”‚ Attribute     β”‚ Value   β”‚
       β”œβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”Όβ”€β”€β”€β”€β”€β”€β”€β”€β”€β”€
       β”‚dl_iterate_phdr()                                                                                                                     β”‚ Thread safety β”‚ MT-Safe β”‚
       β””β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜

CONFORMING TO
       The dl_iterate_phdr() function is not specified in any standard.  Various 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.

EXAMPLES
       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 ad‐
       dress, 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>
       #include <stdint.h>

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

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

           for (int 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:%7jx] flags: %#jx; ", j,
                       (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr),
                       (uintmax_t) info->dlpi_phdr[j].p_memsz,
                       (uintmax_t) info->dlpi_phdr[j].p_flags);
               if (type != NULL)
                   printf("%s\n", type);
               else
                   printf("[other (%#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 locations online.

GNU                                                                            2021-03-22                                                             DL_ITERATE_PHDR(3)