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5a68afcf | 1 | /* Native Client support for ELF |
b90efa5b | 2 | Copyright (C) 2012-2015 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 | |
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" | |
887badb3 | 23 | #include "libbfd.h" |
5a68afcf RM |
24 | #include "elf-bfd.h" |
25 | #include "elf-nacl.h" | |
26 | #include "elf/common.h" | |
27 | #include "elf/internal.h" | |
28 | ||
29 | static bfd_boolean | |
30 | segment_executable (struct elf_segment_map *seg) | |
31 | { | |
32 | if (seg->p_flags_valid) | |
33 | return (seg->p_flags & PF_X) != 0; | |
34 | else | |
35 | { | |
36 | /* The p_flags value has not been computed yet, | |
887badb3 | 37 | so we have to look through the sections. */ |
5a68afcf RM |
38 | unsigned int i; |
39 | for (i = 0; i < seg->count; ++i) | |
887badb3 RM |
40 | if (seg->sections[i]->flags & SEC_CODE) |
41 | return TRUE; | |
5a68afcf RM |
42 | } |
43 | return FALSE; | |
44 | } | |
45 | ||
a3f548ed | 46 | /* Determine if this segment is eligible to receive the file and program |
86e0565d | 47 | headers. It must be read-only and non-executable. |
a0c82a2b RM |
48 | Its first section must start far enough past the page boundary to |
49 | allow space for the headers. */ | |
5a68afcf | 50 | static bfd_boolean |
a3f548ed | 51 | segment_eligible_for_headers (struct elf_segment_map *seg, |
887badb3 | 52 | bfd_vma minpagesize, bfd_vma sizeof_headers) |
5a68afcf | 53 | { |
5a68afcf | 54 | unsigned int i; |
887badb3 | 55 | if (seg->count == 0 || seg->sections[0]->lma % minpagesize < sizeof_headers) |
a3f548ed | 56 | return FALSE; |
5a68afcf RM |
57 | for (i = 0; i < seg->count; ++i) |
58 | { | |
a0c82a2b | 59 | if ((seg->sections[i]->flags & (SEC_CODE|SEC_READONLY)) != SEC_READONLY) |
887badb3 | 60 | return FALSE; |
5a68afcf | 61 | } |
86e0565d | 62 | return TRUE; |
5a68afcf RM |
63 | } |
64 | ||
65 | ||
66 | /* We permute the segment_map to get BFD to do the file layout we want: | |
67 | The first non-executable PT_LOAD segment appears first in the file | |
68 | and contains the ELF file header and phdrs. */ | |
69 | bfd_boolean | |
d324f6d6 | 70 | nacl_modify_segment_map (bfd *abfd, struct bfd_link_info *info) |
5a68afcf | 71 | { |
33aa641a | 72 | const struct elf_backend_data *const bed = get_elf_backend_data (abfd); |
12bd6957 | 73 | struct elf_segment_map **m = &elf_seg_map (abfd); |
5a68afcf RM |
74 | struct elf_segment_map **first_load = NULL; |
75 | struct elf_segment_map **last_load = NULL; | |
76 | bfd_boolean moved_headers = FALSE; | |
33aa641a | 77 | int sizeof_headers; |
5a68afcf | 78 | |
d324f6d6 RM |
79 | if (info != NULL && info->user_phdrs) |
80 | /* The linker script used PHDRS explicitly, so don't change what the | |
81 | user asked for. */ | |
82 | return TRUE; | |
83 | ||
33aa641a RM |
84 | if (info != NULL) |
85 | /* We're doing linking, so evalute SIZEOF_HEADERS as in a linker script. */ | |
86 | sizeof_headers = bfd_sizeof_headers (abfd, info); | |
87 | else | |
88 | { | |
89 | /* We're not doing linking, so this is objcopy or suchlike. | |
90 | We just need to collect the size of the existing headers. */ | |
91 | struct elf_segment_map *seg; | |
92 | sizeof_headers = bed->s->sizeof_ehdr; | |
93 | for (seg = *m; seg != NULL; seg = seg->next) | |
94 | sizeof_headers += bed->s->sizeof_phdr; | |
95 | } | |
96 | ||
5a68afcf RM |
97 | while (*m != NULL) |
98 | { | |
99 | struct elf_segment_map *seg = *m; | |
100 | ||
101 | if (seg->p_type == PT_LOAD) | |
887badb3 RM |
102 | { |
103 | bfd_boolean executable = segment_executable (seg); | |
104 | ||
105 | if (executable | |
106 | && seg->count > 0 | |
33aa641a | 107 | && seg->sections[0]->vma % bed->minpagesize == 0) |
887badb3 RM |
108 | { |
109 | asection *lastsec = seg->sections[seg->count - 1]; | |
110 | bfd_vma end = lastsec->vma + lastsec->size; | |
33aa641a | 111 | if (end % bed->minpagesize != 0) |
887badb3 RM |
112 | { |
113 | /* This is an executable segment that starts on a page | |
114 | boundary but does not end on a page boundary. Fill | |
115 | it out to a whole page with code fill (the tail of | |
116 | the segment will not be within any section). Thus | |
117 | the entire code segment can be mapped from the file | |
118 | as whole pages and that mapping will contain only | |
119 | valid instructions. | |
120 | ||
121 | To accomplish this, we must fake out the code in | |
122 | assign_file_positions_for_load_sections (elf.c) so | |
123 | that it advances past the rest of the final page, | |
124 | rather than trying to put the next (unaligned, or | |
125 | unallocated) section. We do this by appending a | |
126 | dummy section record to this element in the segment | |
127 | map. No such output section ever actually exists, | |
128 | but this gets the layout logic to advance the file | |
129 | positions past this partial page. Since we are | |
130 | lying to BFD like this, nothing will ever know to | |
131 | write the section contents. So we do that by hand | |
132 | after the fact, in nacl_final_write_processing, below. */ | |
133 | ||
134 | struct elf_segment_map *newseg; | |
135 | asection *sec; | |
136 | struct bfd_elf_section_data *secdata; | |
137 | ||
138 | BFD_ASSERT (!seg->p_size_valid); | |
139 | ||
140 | secdata = bfd_zalloc (abfd, sizeof *secdata); | |
141 | if (secdata == NULL) | |
142 | return FALSE; | |
143 | ||
144 | sec = bfd_zalloc (abfd, sizeof *sec); | |
145 | if (sec == NULL) | |
146 | return FALSE; | |
147 | ||
148 | /* Fill in only the fields that actually affect the logic | |
149 | in assign_file_positions_for_load_sections. */ | |
150 | sec->vma = end; | |
151 | sec->lma = lastsec->lma + lastsec->size; | |
33aa641a | 152 | sec->size = bed->minpagesize - (end % bed->minpagesize); |
887badb3 RM |
153 | sec->flags = (SEC_ALLOC | SEC_LOAD |
154 | | SEC_READONLY | SEC_CODE | SEC_LINKER_CREATED); | |
155 | sec->used_by_bfd = secdata; | |
156 | ||
157 | secdata->this_hdr.sh_type = SHT_PROGBITS; | |
158 | secdata->this_hdr.sh_flags = SHF_ALLOC | SHF_EXECINSTR; | |
159 | secdata->this_hdr.sh_addr = sec->vma; | |
160 | secdata->this_hdr.sh_size = sec->size; | |
161 | ||
162 | newseg = bfd_alloc (abfd, | |
163 | sizeof *newseg + ((seg->count + 1) | |
164 | * sizeof (asection *))); | |
165 | if (newseg == NULL) | |
166 | return FALSE; | |
167 | memcpy (newseg, seg, | |
168 | sizeof *newseg + (seg->count * sizeof (asection *))); | |
169 | newseg->sections[newseg->count++] = sec; | |
170 | *m = seg = newseg; | |
171 | } | |
172 | } | |
173 | ||
174 | /* First, we're just finding the earliest PT_LOAD. | |
175 | By the normal rules, this will be the lowest-addressed one. | |
176 | We only have anything interesting to do if it's executable. */ | |
177 | last_load = m; | |
178 | if (first_load == NULL) | |
179 | { | |
180 | if (!executable) | |
181 | goto next; | |
182 | first_load = m; | |
183 | } | |
184 | /* Now that we've noted the first PT_LOAD, we're looking for | |
185 | the first non-executable PT_LOAD with a nonempty p_filesz. */ | |
186 | else if (!moved_headers | |
33aa641a | 187 | && segment_eligible_for_headers (seg, bed->minpagesize, |
887badb3 RM |
188 | sizeof_headers)) |
189 | { | |
190 | /* This is the one we were looking for! | |
191 | ||
192 | First, clear the flags on previous segments that | |
193 | say they include the file header and phdrs. */ | |
194 | struct elf_segment_map *prevseg; | |
195 | for (prevseg = *first_load; | |
196 | prevseg != seg; | |
197 | prevseg = prevseg->next) | |
198 | if (prevseg->p_type == PT_LOAD) | |
199 | { | |
200 | prevseg->includes_filehdr = 0; | |
201 | prevseg->includes_phdrs = 0; | |
202 | } | |
203 | ||
204 | /* This segment will include those headers instead. */ | |
205 | seg->includes_filehdr = 1; | |
206 | seg->includes_phdrs = 1; | |
207 | ||
208 | moved_headers = TRUE; | |
209 | } | |
210 | } | |
211 | ||
212 | next: | |
5a68afcf RM |
213 | m = &seg->next; |
214 | } | |
215 | ||
216 | if (first_load != last_load && moved_headers) | |
217 | { | |
218 | /* Now swap the first and last PT_LOAD segments' | |
887badb3 | 219 | positions in segment_map. */ |
5a68afcf RM |
220 | struct elf_segment_map *first = *first_load; |
221 | struct elf_segment_map *last = *last_load; | |
222 | *first_load = first->next; | |
223 | first->next = last->next; | |
224 | last->next = first; | |
225 | } | |
226 | ||
227 | return TRUE; | |
228 | } | |
229 | ||
230 | /* After nacl_modify_segment_map has done its work, the file layout has | |
231 | been done as we wanted. But the PT_LOAD phdrs are no longer in the | |
232 | proper order for the ELF rule that they must appear in ascending address | |
233 | order. So find the two segments we swapped before, and swap them back. */ | |
234 | bfd_boolean | |
aa6407c6 | 235 | nacl_modify_program_headers (bfd *abfd, struct bfd_link_info *info) |
5a68afcf | 236 | { |
12bd6957 | 237 | struct elf_segment_map **m = &elf_seg_map (abfd); |
5a68afcf RM |
238 | Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr; |
239 | Elf_Internal_Phdr *p = phdr; | |
240 | ||
d324f6d6 RM |
241 | if (info != NULL && info->user_phdrs) |
242 | /* The linker script used PHDRS explicitly, so don't change what the | |
243 | user asked for. */ | |
244 | return TRUE; | |
245 | ||
5a68afcf RM |
246 | /* Find the PT_LOAD that contains the headers (should be the first). */ |
247 | while (*m != NULL) | |
248 | { | |
249 | if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr) | |
887badb3 | 250 | break; |
5a68afcf RM |
251 | |
252 | m = &(*m)->next; | |
253 | ++p; | |
254 | } | |
255 | ||
256 | if (*m != NULL) | |
257 | { | |
258 | struct elf_segment_map **first_load_seg = m; | |
259 | Elf_Internal_Phdr *first_load_phdr = p; | |
260 | struct elf_segment_map **next_load_seg = NULL; | |
261 | Elf_Internal_Phdr *next_load_phdr = NULL; | |
262 | ||
263 | /* Now move past that first one and find the PT_LOAD that should be | |
887badb3 | 264 | before it by address order. */ |
5a68afcf RM |
265 | |
266 | m = &(*m)->next; | |
267 | ++p; | |
268 | ||
887badb3 RM |
269 | while (*m != NULL) |
270 | { | |
271 | if (p->p_type == PT_LOAD && p->p_vaddr < first_load_phdr->p_vaddr) | |
272 | { | |
273 | next_load_seg = m; | |
274 | next_load_phdr = p; | |
275 | break; | |
276 | } | |
5a68afcf | 277 | |
887badb3 RM |
278 | m = &(*m)->next; |
279 | ++p; | |
280 | } | |
5a68afcf RM |
281 | |
282 | /* Swap their positions in the segment_map back to how they used to be. | |
887badb3 RM |
283 | The phdrs have already been set up by now, so we have to slide up |
284 | the earlier ones to insert the one that should be first. */ | |
5a68afcf | 285 | if (next_load_seg != NULL) |
887badb3 RM |
286 | { |
287 | Elf_Internal_Phdr move_phdr; | |
288 | struct elf_segment_map *first_seg = *first_load_seg; | |
289 | struct elf_segment_map *next_seg = *next_load_seg; | |
290 | struct elf_segment_map *first_next = first_seg->next; | |
291 | struct elf_segment_map *next_next = next_seg->next; | |
292 | ||
293 | if (next_load_seg == &first_seg->next) | |
294 | { | |
295 | *first_load_seg = next_seg; | |
296 | next_seg->next = first_seg; | |
297 | first_seg->next = next_next; | |
298 | } | |
299 | else | |
300 | { | |
301 | *first_load_seg = first_next; | |
302 | *next_load_seg = next_next; | |
303 | ||
304 | first_seg->next = *next_load_seg; | |
305 | *next_load_seg = first_seg; | |
306 | ||
307 | next_seg->next = *first_load_seg; | |
308 | *first_load_seg = next_seg; | |
309 | } | |
310 | ||
311 | move_phdr = *next_load_phdr; | |
312 | memmove (first_load_phdr + 1, first_load_phdr, | |
313 | (next_load_phdr - first_load_phdr) * sizeof move_phdr); | |
314 | *first_load_phdr = move_phdr; | |
315 | } | |
5a68afcf RM |
316 | } |
317 | ||
318 | return TRUE; | |
319 | } | |
887badb3 RM |
320 | |
321 | void | |
322 | nacl_final_write_processing (bfd *abfd, bfd_boolean linker ATTRIBUTE_UNUSED) | |
323 | { | |
324 | struct elf_segment_map *seg; | |
325 | for (seg = elf_seg_map (abfd); seg != NULL; seg = seg->next) | |
326 | if (seg->p_type == PT_LOAD | |
327 | && seg->count > 1 | |
328 | && seg->sections[seg->count - 1]->owner == NULL) | |
329 | { | |
330 | /* This is a fake section added in nacl_modify_segment_map, above. | |
331 | It's not a real BFD section, so nothing wrote its contents. | |
332 | Now write out its contents. */ | |
333 | ||
334 | asection *sec = seg->sections[seg->count - 1]; | |
335 | char *fill; | |
336 | ||
337 | BFD_ASSERT (sec->flags & SEC_LINKER_CREATED); | |
338 | BFD_ASSERT (sec->flags & SEC_CODE); | |
339 | BFD_ASSERT (sec->size > 0); | |
340 | ||
341 | fill = abfd->arch_info->fill (sec->size, bfd_big_endian (abfd), TRUE); | |
342 | ||
343 | if (fill == NULL | |
344 | || bfd_seek (abfd, sec->filepos, SEEK_SET) != 0 | |
345 | || bfd_bwrite (fill, sec->size, abfd) != sec->size) | |
346 | { | |
347 | /* We don't have a proper way to report an error here. So | |
348 | instead fudge things so that elf_write_shdrs_and_ehdr will | |
349 | fail. */ | |
350 | elf_elfheader (abfd)->e_shoff = (file_ptr) -1; | |
351 | } | |
352 | ||
353 | free (fill); | |
354 | } | |
355 | } |