elf/dl-reloc-static-pie.c

   1 /* Support for relocating static PIE.
   2    Copyright (C) 2017-2025 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #if ENABLE_STATIC_PIE
  20 /* Mark symbols hidden in static PIE for early self relocation to work.  */
  21 # pragma GCC visibility push(hidden)
  22 #include <assert.h>
  23 #include <unistd.h>
  24 #include <ldsodefs.h>
  25
  26 #include <dl-machine.h>
  27 #include <dl-debug.h>
  28
  29 #define RESOLVE_MAP(map, scope, sym, version, flags) map
  30 #include "dynamic-link.h"
  31 #include "get-dynamic-info.h"
  32
  33 /* Relocate static executable with PIE.  */
  34
  35 void
  36 _dl_relocate_static_pie (void)
  37 {
  38   struct link_map *main_map = _dl_get_dl_main_map ();
  39
  40   /* NB: elf_machine_load_address () returns the run-time load address
  41      of static PIE.  The l_addr field contains the difference between the
  42      link-time load address in the ELF file and the run-time load address
  43      in memory.  We must subtract the link-time load address of static PIE,
  44      which can be non-zero, when computing the l_addr field.  Since static
  45      PIE usually doesn't have PT_PHDR segment, use p_vaddr of the PT_LOAD
  46      segment with offset == 0 as the load address of static PIE.  */
  47   ElfW(Addr) file_p_vaddr = 0;
  48   const ElfW(Phdr) *ph, *phdr = GL(dl_phdr);
  49   size_t phnum = GL(dl_phnum);
  50   for (ph = phdr; ph < &phdr[phnum]; ++ph)
  51     switch (ph->p_type)
  52       {
  53       case PT_LOAD:
  54         if (ph->p_offset == 0)
  55           file_p_vaddr = ph->p_vaddr;
  56         break;
  57       case PT_DYNAMIC:
  58         main_map->l_ld_readonly = (ph->p_flags & PF_W) == 0;
  59         break;
  60       default:
  61         break;
  62       }
  63
  64   /* Figure out the run-time load address of static PIE.  */
  65   ElfW(Addr) l_addr = elf_machine_load_address ();
  66   main_map->l_addr = l_addr - file_p_vaddr;
  67
  68   /* Read our own dynamic section and fill in the info array.  */
  69   main_map->l_ld = ((void *) l_addr + elf_machine_dynamic ());
  70
  71   elf_get_dynamic_info (main_map, false, true);
  72
  73 # ifdef ELF_MACHINE_BEFORE_RTLD_RELOC
  74   ELF_MACHINE_BEFORE_RTLD_RELOC (main_map, main_map->l_info);
  75 # endif
  76
  77   /* Relocate ourselves so we can do normal function calls and
  78      data access using the global offset table.  */
  79   ELF_DYNAMIC_RELOCATE (main_map, NULL, 0, 0, 0);
  80   main_map->l_relocated = 1;
  81
  82   /* Initialize _r_debug_extended.  */
  83   struct r_debug *r = _dl_debug_initialize (0, LM_ID_BASE);
  84   r->r_state = RT_CONSISTENT;
  85
  86   /* Set up debugging before the debugger is notified for the first
  87      time.  */
  88   elf_setup_debug_entry (main_map, r);
  89 }
  90 #endif