1 /* Native Client support for ELF 2 Copyright 2012 Free Software Foundation, Inc. 3 4 This file is part of BFD, the Binary File Descriptor library. 5 6 This program is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3 of the License, or 9 (at your option) any later version. 10 11 This program is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 GNU General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with this program; if not, write to the Free Software 18 Foundation, Inc., 59 Temple Place - Suite 330, Boston, 19 MA 02111-1307, USA. */ 20 21 #include "sysdep.h" 22 #include "bfd.h" 23 #include "elf-bfd.h" 24 #include "elf-nacl.h" 25 #include "elf/common.h" 26 #include "elf/internal.h" 27 28 static bfd_boolean 29 segment_executable (struct elf_segment_map *seg) 30 { 31 if (seg->p_flags_valid) 32 return (seg->p_flags & PF_X) != 0; 33 else 34 { 35 /* The p_flags value has not been computed yet, 36 so we have to look through the sections. */ 37 unsigned int i; 38 for (i = 0; i < seg->count; ++i) 39 if (seg->sections[i]->flags & SEC_CODE) 40 return TRUE; 41 } 42 return FALSE; 43 } 44 45 /* Determine if this segment is eligible to receive the file and program 46 headers. It must be read-only, non-executable, and have contents. 47 Its first section must start far enough past the page boundary to 48 allow space for the headers. */ 49 static bfd_boolean 50 segment_eligible_for_headers (struct elf_segment_map *seg, 51 bfd_vma maxpagesize, bfd_vma sizeof_headers) 52 { 53 bfd_boolean any_contents = FALSE; 54 unsigned int i; 55 if (seg->count == 0 || seg->sections[0]->lma % maxpagesize < sizeof_headers) 56 return FALSE; 57 for (i = 0; i < seg->count; ++i) 58 { 59 if ((seg->sections[i]->flags & (SEC_CODE|SEC_READONLY)) != SEC_READONLY) 60 return FALSE; 61 if (seg->sections[i]->flags & SEC_HAS_CONTENTS) 62 any_contents = TRUE; 63 } 64 return any_contents; 65 } 66 67 68 /* We permute the segment_map to get BFD to do the file layout we want: 69 The first non-executable PT_LOAD segment appears first in the file 70 and contains the ELF file header and phdrs. */ 71 bfd_boolean 72 nacl_modify_segment_map (bfd *abfd, struct bfd_link_info *info) 73 { 74 struct elf_segment_map **m = &elf_seg_map (abfd); 75 struct elf_segment_map **first_load = NULL; 76 struct elf_segment_map **last_load = NULL; 77 bfd_boolean moved_headers = FALSE; 78 int sizeof_headers = info == NULL ? 0 : bfd_sizeof_headers (abfd, info); 79 bfd_vma maxpagesize = get_elf_backend_data (abfd)->maxpagesize; 80 81 if (info != NULL && info->user_phdrs) 82 /* The linker script used PHDRS explicitly, so don't change what the 83 user asked for. */ 84 return TRUE; 85 86 while (*m != NULL) 87 { 88 struct elf_segment_map *seg = *m; 89 90 if (seg->p_type == PT_LOAD) 91 { 92 /* First, we're just finding the earliest PT_LOAD. 93 By the normal rules, this will be the lowest-addressed one. 94 We only have anything interesting to do if it's executable. */ 95 last_load = m; 96 if (first_load == NULL) 97 { 98 if (!segment_executable (*m)) 99 return TRUE; 100 first_load = m; 101 } 102 /* Now that we've noted the first PT_LOAD, we're looking for 103 the first non-executable PT_LOAD with a nonempty p_filesz. */ 104 else if (!moved_headers 105 && segment_eligible_for_headers (seg, maxpagesize, 106 sizeof_headers)) 107 { 108 /* This is the one we were looking for! 109 110 First, clear the flags on previous segments that 111 say they include the file header and phdrs. */ 112 struct elf_segment_map *prevseg; 113 for (prevseg = *first_load; 114 prevseg != seg; 115 prevseg = prevseg->next) 116 if (prevseg->p_type == PT_LOAD) 117 { 118 prevseg->includes_filehdr = 0; 119 prevseg->includes_phdrs = 0; 120 } 121 122 /* This segment will include those headers instead. */ 123 seg->includes_filehdr = 1; 124 seg->includes_phdrs = 1; 125 126 moved_headers = TRUE; 127 } 128 } 129 130 m = &seg->next; 131 } 132 133 if (first_load != last_load && moved_headers) 134 { 135 /* Now swap the first and last PT_LOAD segments' 136 positions in segment_map. */ 137 struct elf_segment_map *first = *first_load; 138 struct elf_segment_map *last = *last_load; 139 *first_load = first->next; 140 first->next = last->next; 141 last->next = first; 142 } 143 144 return TRUE; 145 } 146 147 /* After nacl_modify_segment_map has done its work, the file layout has 148 been done as we wanted. But the PT_LOAD phdrs are no longer in the 149 proper order for the ELF rule that they must appear in ascending address 150 order. So find the two segments we swapped before, and swap them back. */ 151 bfd_boolean 152 nacl_modify_program_headers (bfd *abfd, struct bfd_link_info *info) 153 { 154 struct elf_segment_map **m = &elf_seg_map (abfd); 155 Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr; 156 Elf_Internal_Phdr *p = phdr; 157 158 if (info != NULL && info->user_phdrs) 159 /* The linker script used PHDRS explicitly, so don't change what the 160 user asked for. */ 161 return TRUE; 162 163 /* Find the PT_LOAD that contains the headers (should be the first). */ 164 while (*m != NULL) 165 { 166 if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr) 167 break; 168 169 m = &(*m)->next; 170 ++p; 171 } 172 173 if (*m != NULL) 174 { 175 struct elf_segment_map **first_load_seg = m; 176 Elf_Internal_Phdr *first_load_phdr = p; 177 struct elf_segment_map **next_load_seg = NULL; 178 Elf_Internal_Phdr *next_load_phdr = NULL; 179 180 /* Now move past that first one and find the PT_LOAD that should be 181 before it by address order. */ 182 183 m = &(*m)->next; 184 ++p; 185 186 while ((*m) != NULL) 187 { 188 if (p->p_type == PT_LOAD && p->p_vaddr < first_load_phdr->p_vaddr) 189 { 190 next_load_seg = m; 191 next_load_phdr = p; 192 break; 193 } 194 195 m = &(*m)->next; 196 ++p; 197 } 198 199 /* Swap their positions in the segment_map back to how they used to be. 200 The phdrs have already been set up by now, so we have to slide up 201 the earlier ones to insert the one that should be first. */ 202 if (next_load_seg != NULL) 203 { 204 Elf_Internal_Phdr move_phdr; 205 struct elf_segment_map *first_seg = *first_load_seg; 206 struct elf_segment_map *next_seg = *next_load_seg; 207 struct elf_segment_map *first_next = first_seg->next; 208 struct elf_segment_map *next_next = next_seg->next; 209 210 first_seg->next = next_next; 211 *first_load_seg = next_seg; 212 213 next_seg->next = first_next; 214 *next_load_seg = first_seg; 215 216 move_phdr = *next_load_phdr; 217 memmove (first_load_phdr + 1, first_load_phdr, 218 (next_load_phdr - first_load_phdr) * sizeof move_phdr); 219 *first_load_phdr = move_phdr; 220 } 221 } 222 223 return TRUE; 224 } 225