# dl_iterate_phdr

## NAME



           dl_iterate_phdr - walk through list of shared objects
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#define _GNU_SOURCE** /* See feature_test_macros(7) */
           **#include <link.h>**
    
           **int dl_iterate_phdr(**
                    **typeof(int (struct dl_phdr_info ***_info_**, size_t** _size_**, void ***_data_**))**
                        *****_callback_**,**
                    **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_.
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌──────────────────────────────────────┬───────────────┬─────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────────┼───────────────┼─────────┤
           │ **dl_iterate_phdr**()                    │ Thread safety │ MT-Safe │
           └──────────────────────────────────────┴───────────────┴─────────┘
    


## VERSIONS



           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.
    
           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.
    


## STANDARDS



           None.
    


## NOTES



           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 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 <stdint.h>
           #include <stdio.h>
           #include <stdlib.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 (size_t 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("    %2zu: [%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(void)
           {
               dl_iterate_phdr(callback, NULL);
    
               exit(EXIT_SUCCESS);
           }
    


* * *