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5a68afcf | 1 | /* Native Client support for ELF |
82704155 | 2 | Copyright (C) 2012-2019 Free Software Foundation, Inc. |
5a68afcf RM |
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/>. */ |
5a68afcf RM |
18 | |
19 | #include "sysdep.h" | |
20 | #include "bfd.h" | |
887badb3 | 21 | #include "libbfd.h" |
5a68afcf RM |
22 | #include "elf-bfd.h" |
23 | #include "elf-nacl.h" | |
24 | #include "elf/common.h" | |
25 | #include "elf/internal.h" | |
26 | ||
27 | static bfd_boolean | |
28 | segment_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. */ |
5a68afcf RM |
36 | unsigned int i; |
37 | for (i = 0; i < seg->count; ++i) | |
887badb3 RM |
38 | if (seg->sections[i]->flags & SEC_CODE) |
39 | return TRUE; | |
5a68afcf RM |
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. |
a0c82a2b RM |
46 | Its first section must start far enough past the page boundary to |
47 | allow space for the headers. */ | |
5a68afcf | 48 | static bfd_boolean |
a3f548ed | 49 | segment_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; |
5a68afcf RM |
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; |
5a68afcf RM |
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. */ | |
67 | bfd_boolean | |
d324f6d6 | 68 | nacl_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 RM |
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 RM |
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 | ||
5a68afcf RM |
94 | while (*m != NULL) |
95 | { | |
96 | struct elf_segment_map *seg = *m; | |
97 | ||
98 | if (seg->p_type == PT_LOAD) | |
887badb3 RM |
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) |
887badb3 RM |
105 | { |
106 | asection *lastsec = seg->sections[seg->count - 1]; | |
107 | bfd_vma end = lastsec->vma + lastsec->size; | |
33aa641a | 108 | if (end % bed->minpagesize != 0) |
887badb3 RM |
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); |
887badb3 RM |
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 AM |
174 | first_load = m; |
175 | ||
887badb3 RM |
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 | } |
5a68afcf RM |
183 | m = &seg->next; |
184 | } | |
185 | ||
64029e93 | 186 | if (headers != NULL) |
5a68afcf | 187 | { |
64029e93 AM |
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 AM |
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 | } | |
5a68afcf RM |
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. */ | |
237 | bfd_boolean | |
6d6c25c8 | 238 | nacl_modify_headers (bfd *abfd, struct bfd_link_info *info) |
5a68afcf | 239 | { |
d324f6d6 RM |
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 AM |
243 | ; |
244 | else | |
5a68afcf | 245 | { |
6d6c25c8 AM |
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 RM |
251 | while (*m != NULL) |
252 | { | |
6d6c25c8 AM |
253 | if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr) |
254 | break; | |
5a68afcf | 255 | |
887badb3 RM |
256 | m = &(*m)->next; |
257 | ++p; | |
258 | } | |
5a68afcf | 259 | |
6d6c25c8 | 260 | if (*m != NULL) |
887badb3 | 261 | { |
6d6c25c8 AM |
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 AM |
270 | m = &(*m)->next; |
271 | ++p; | |
272 | ||
273 | while (*m != NULL) | |
887badb3 | 274 | { |
6d6c25c8 AM |
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 AM |
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 AM |
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 AM |
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 AM |
309 | first_seg->next = *next_load_seg; |
310 | *next_load_seg = first_seg; | |
887badb3 | 311 | |
6d6c25c8 AM |
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 | } |
5a68afcf RM |
322 | } |
323 | ||
6d6c25c8 | 324 | return _bfd_elf_modify_headers (abfd, info); |
5a68afcf | 325 | } |
887badb3 | 326 | |
cc364be6 AM |
327 | bfd_boolean |
328 | nacl_final_write_processing (bfd *abfd) | |
887badb3 RM |
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 | } |