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[deliverable/binutils-gdb.git] / bfd / elf-nacl.c
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5a68afcf 1/* Native Client support for ELF
82704155 2 Copyright (C) 2012-2019 Free Software Foundation, Inc.
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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
08832196 17 along with this program. If not, see <http://www.gnu.org/licenses/>. */
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18
19#include "sysdep.h"
20#include "bfd.h"
887badb3 21#include "libbfd.h"
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22#include "elf-bfd.h"
23#include "elf-nacl.h"
24#include "elf/common.h"
25#include "elf/internal.h"
26
27static bfd_boolean
28segment_executable (struct elf_segment_map *seg)
29{
30 if (seg->p_flags_valid)
31 return (seg->p_flags & PF_X) != 0;
32 else
33 {
34 /* The p_flags value has not been computed yet,
887badb3 35 so we have to look through the sections. */
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36 unsigned int i;
37 for (i = 0; i < seg->count; ++i)
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38 if (seg->sections[i]->flags & SEC_CODE)
39 return TRUE;
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40 }
41 return FALSE;
42}
43
a3f548ed 44/* Determine if this segment is eligible to receive the file and program
86e0565d 45 headers. It must be read-only and non-executable.
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46 Its first section must start far enough past the page boundary to
47 allow space for the headers. */
5a68afcf 48static bfd_boolean
a3f548ed 49segment_eligible_for_headers (struct elf_segment_map *seg,
887badb3 50 bfd_vma minpagesize, bfd_vma sizeof_headers)
5a68afcf 51{
5a68afcf 52 unsigned int i;
887badb3 53 if (seg->count == 0 || seg->sections[0]->lma % minpagesize < sizeof_headers)
a3f548ed 54 return FALSE;
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55 for (i = 0; i < seg->count; ++i)
56 {
a0c82a2b 57 if ((seg->sections[i]->flags & (SEC_CODE|SEC_READONLY)) != SEC_READONLY)
887badb3 58 return FALSE;
5a68afcf 59 }
86e0565d 60 return TRUE;
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61}
62
63
64/* We permute the segment_map to get BFD to do the file layout we want:
65 The first non-executable PT_LOAD segment appears first in the file
66 and contains the ELF file header and phdrs. */
67bfd_boolean
d324f6d6 68nacl_modify_segment_map (bfd *abfd, struct bfd_link_info *info)
5a68afcf 69{
33aa641a 70 const struct elf_backend_data *const bed = get_elf_backend_data (abfd);
12bd6957 71 struct elf_segment_map **m = &elf_seg_map (abfd);
5a68afcf 72 struct elf_segment_map **first_load = NULL;
64029e93 73 struct elf_segment_map **headers = NULL;
33aa641a 74 int sizeof_headers;
5a68afcf 75
d324f6d6
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76 if (info != NULL && info->user_phdrs)
77 /* The linker script used PHDRS explicitly, so don't change what the
78 user asked for. */
79 return TRUE;
80
33aa641a
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81 if (info != NULL)
82 /* We're doing linking, so evalute SIZEOF_HEADERS as in a linker script. */
83 sizeof_headers = bfd_sizeof_headers (abfd, info);
84 else
85 {
86 /* We're not doing linking, so this is objcopy or suchlike.
87 We just need to collect the size of the existing headers. */
88 struct elf_segment_map *seg;
89 sizeof_headers = bed->s->sizeof_ehdr;
90 for (seg = *m; seg != NULL; seg = seg->next)
91 sizeof_headers += bed->s->sizeof_phdr;
92 }
93
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94 while (*m != NULL)
95 {
96 struct elf_segment_map *seg = *m;
97
98 if (seg->p_type == PT_LOAD)
887badb3
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99 {
100 bfd_boolean executable = segment_executable (seg);
101
102 if (executable
103 && seg->count > 0
33aa641a 104 && seg->sections[0]->vma % bed->minpagesize == 0)
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105 {
106 asection *lastsec = seg->sections[seg->count - 1];
107 bfd_vma end = lastsec->vma + lastsec->size;
33aa641a 108 if (end % bed->minpagesize != 0)
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109 {
110 /* This is an executable segment that starts on a page
111 boundary but does not end on a page boundary. Fill
112 it out to a whole page with code fill (the tail of
113 the segment will not be within any section). Thus
114 the entire code segment can be mapped from the file
115 as whole pages and that mapping will contain only
116 valid instructions.
117
118 To accomplish this, we must fake out the code in
119 assign_file_positions_for_load_sections (elf.c) so
120 that it advances past the rest of the final page,
121 rather than trying to put the next (unaligned, or
122 unallocated) section. We do this by appending a
123 dummy section record to this element in the segment
124 map. No such output section ever actually exists,
125 but this gets the layout logic to advance the file
126 positions past this partial page. Since we are
127 lying to BFD like this, nothing will ever know to
128 write the section contents. So we do that by hand
129 after the fact, in nacl_final_write_processing, below. */
130
131 struct elf_segment_map *newseg;
132 asection *sec;
133 struct bfd_elf_section_data *secdata;
134
135 BFD_ASSERT (!seg->p_size_valid);
136
137 secdata = bfd_zalloc (abfd, sizeof *secdata);
138 if (secdata == NULL)
139 return FALSE;
140
141 sec = bfd_zalloc (abfd, sizeof *sec);
142 if (sec == NULL)
143 return FALSE;
144
145 /* Fill in only the fields that actually affect the logic
146 in assign_file_positions_for_load_sections. */
147 sec->vma = end;
148 sec->lma = lastsec->lma + lastsec->size;
33aa641a 149 sec->size = bed->minpagesize - (end % bed->minpagesize);
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150 sec->flags = (SEC_ALLOC | SEC_LOAD
151 | SEC_READONLY | SEC_CODE | SEC_LINKER_CREATED);
152 sec->used_by_bfd = secdata;
153
154 secdata->this_hdr.sh_type = SHT_PROGBITS;
155 secdata->this_hdr.sh_flags = SHF_ALLOC | SHF_EXECINSTR;
156 secdata->this_hdr.sh_addr = sec->vma;
157 secdata->this_hdr.sh_size = sec->size;
158
159 newseg = bfd_alloc (abfd,
160 sizeof *newseg + ((seg->count + 1)
161 * sizeof (asection *)));
162 if (newseg == NULL)
163 return FALSE;
164 memcpy (newseg, seg,
165 sizeof *newseg + (seg->count * sizeof (asection *)));
166 newseg->sections[newseg->count++] = sec;
167 *m = seg = newseg;
168 }
169 }
170
171 /* First, we're just finding the earliest PT_LOAD.
64029e93 172 By the normal rules, this will be the lowest-addressed one. */
887badb3 173 if (first_load == NULL)
64029e93
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174 first_load = m;
175
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176 /* Now that we've noted the first PT_LOAD, we're looking for
177 the first non-executable PT_LOAD with a nonempty p_filesz. */
64029e93 178 else if (headers == NULL
33aa641a 179 && segment_eligible_for_headers (seg, bed->minpagesize,
887badb3 180 sizeof_headers))
64029e93 181 headers = m;
887badb3 182 }
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183 m = &seg->next;
184 }
185
64029e93 186 if (headers != NULL)
5a68afcf 187 {
64029e93
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188 struct elf_segment_map **last_load = NULL;
189 struct elf_segment_map *seg;
190
191 m = first_load;
192 while ((seg = *m) != NULL)
193 {
194 if (seg->p_type == PT_LOAD)
195 {
196 /* Clear the flags on any previous segment that
197 included the file header and phdrs. */
198 seg->includes_filehdr = 0;
199 seg->includes_phdrs = 0;
30fe1832 200 seg->no_sort_lma = 1;
64029e93
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201 /* Also strip out empty segments. */
202 if (seg->count == 0)
203 {
204 if (headers == &seg->next)
205 headers = m;
206 *m = seg->next;
207 continue;
208 }
209 last_load = m;
210 }
211 m = &seg->next;
212 }
213
214 /* This segment will include those headers instead. */
215 seg = *headers;
216 seg->includes_filehdr = 1;
217 seg->includes_phdrs = 1;
218
219 if (last_load != NULL && first_load != last_load && first_load != headers)
220 {
221 /* Put the first PT_LOAD header last. */
222 struct elf_segment_map *first = *first_load;
223 struct elf_segment_map *last = *last_load;
224 *first_load = first->next;
225 first->next = last->next;
226 last->next = first;
227 }
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228 }
229
230 return TRUE;
231}
232
233/* After nacl_modify_segment_map has done its work, the file layout has
234 been done as we wanted. But the PT_LOAD phdrs are no longer in the
235 proper order for the ELF rule that they must appear in ascending address
236 order. So find the two segments we swapped before, and swap them back. */
237bfd_boolean
6d6c25c8 238nacl_modify_headers (bfd *abfd, struct bfd_link_info *info)
5a68afcf 239{
d324f6d6
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240 if (info != NULL && info->user_phdrs)
241 /* The linker script used PHDRS explicitly, so don't change what the
242 user asked for. */
6d6c25c8
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243 ;
244 else
5a68afcf 245 {
6d6c25c8
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246 struct elf_segment_map **m = &elf_seg_map (abfd);
247 Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr;
248 Elf_Internal_Phdr *p = phdr;
5a68afcf 249
6d6c25c8 250 /* Find the PT_LOAD that contains the headers (should be the first). */
887badb3
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251 while (*m != NULL)
252 {
6d6c25c8
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253 if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr)
254 break;
5a68afcf 255
887badb3
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256 m = &(*m)->next;
257 ++p;
258 }
5a68afcf 259
6d6c25c8 260 if (*m != NULL)
887badb3 261 {
6d6c25c8
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262 struct elf_segment_map **first_load_seg = m;
263 Elf_Internal_Phdr *first_load_phdr = p;
264 struct elf_segment_map **next_load_seg = NULL;
265 Elf_Internal_Phdr *next_load_phdr = NULL;
266
267 /* Now move past that first one and find the PT_LOAD that should be
268 before it by address order. */
887badb3 269
6d6c25c8
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270 m = &(*m)->next;
271 ++p;
272
273 while (*m != NULL)
887badb3 274 {
6d6c25c8
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275 if (p->p_type == PT_LOAD && p->p_vaddr < first_load_phdr->p_vaddr)
276 {
277 next_load_seg = m;
278 next_load_phdr = p;
279 break;
280 }
281
282 m = &(*m)->next;
283 ++p;
887badb3 284 }
6d6c25c8
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285
286 /* Swap their positions in the segment_map back to how they
287 used to be. The phdrs have already been set up by now,
288 so we have to slide up the earlier ones to insert the one
289 that should be first. */
290 if (next_load_seg != NULL)
887badb3 291 {
6d6c25c8
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292 Elf_Internal_Phdr move_phdr;
293 struct elf_segment_map *first_seg = *first_load_seg;
294 struct elf_segment_map *next_seg = *next_load_seg;
295 struct elf_segment_map *first_next = first_seg->next;
296 struct elf_segment_map *next_next = next_seg->next;
887badb3 297
6d6c25c8
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298 if (next_load_seg == &first_seg->next)
299 {
300 *first_load_seg = next_seg;
301 next_seg->next = first_seg;
302 first_seg->next = next_next;
303 }
304 else
305 {
306 *first_load_seg = first_next;
307 *next_load_seg = next_next;
887badb3 308
6d6c25c8
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309 first_seg->next = *next_load_seg;
310 *next_load_seg = first_seg;
887badb3 311
6d6c25c8
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312 next_seg->next = *first_load_seg;
313 *first_load_seg = next_seg;
314 }
315
316 move_phdr = *next_load_phdr;
317 memmove (first_load_phdr + 1, first_load_phdr,
318 (next_load_phdr - first_load_phdr) * sizeof move_phdr);
319 *first_load_phdr = move_phdr;
320 }
887badb3 321 }
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322 }
323
6d6c25c8 324 return _bfd_elf_modify_headers (abfd, info);
5a68afcf 325}
887badb3 326
cc364be6
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327bfd_boolean
328nacl_final_write_processing (bfd *abfd)
887badb3
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329{
330 struct elf_segment_map *seg;
331 for (seg = elf_seg_map (abfd); seg != NULL; seg = seg->next)
332 if (seg->p_type == PT_LOAD
333 && seg->count > 1
334 && seg->sections[seg->count - 1]->owner == NULL)
335 {
336 /* This is a fake section added in nacl_modify_segment_map, above.
337 It's not a real BFD section, so nothing wrote its contents.
338 Now write out its contents. */
339
340 asection *sec = seg->sections[seg->count - 1];
341 char *fill;
342
343 BFD_ASSERT (sec->flags & SEC_LINKER_CREATED);
344 BFD_ASSERT (sec->flags & SEC_CODE);
345 BFD_ASSERT (sec->size > 0);
346
347 fill = abfd->arch_info->fill (sec->size, bfd_big_endian (abfd), TRUE);
348
349 if (fill == NULL
350 || bfd_seek (abfd, sec->filepos, SEEK_SET) != 0
351 || bfd_bwrite (fill, sec->size, abfd) != sec->size)
352 {
353 /* We don't have a proper way to report an error here. So
354 instead fudge things so that elf_write_shdrs_and_ehdr will
355 fail. */
356 elf_elfheader (abfd)->e_shoff = (file_ptr) -1;
357 }
358
359 free (fill);
360 }
cc364be6 361 return _bfd_elf_final_write_processing (abfd);
887badb3 362}
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