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5a68afcf | 1 | /* Native Client support for ELF |
887badb3 | 2 | Copyright 2012, 2013 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 | { |
12bd6957 | 72 | struct elf_segment_map **m = &elf_seg_map (abfd); |
5a68afcf RM |
73 | struct elf_segment_map **first_load = NULL; |
74 | struct elf_segment_map **last_load = NULL; | |
75 | bfd_boolean moved_headers = FALSE; | |
aa6407c6 | 76 | int sizeof_headers = info == NULL ? 0 : bfd_sizeof_headers (abfd, info); |
887badb3 | 77 | bfd_vma minpagesize = get_elf_backend_data (abfd)->minpagesize; |
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 | ||
5a68afcf RM |
84 | while (*m != NULL) |
85 | { | |
86 | struct elf_segment_map *seg = *m; | |
87 | ||
88 | if (seg->p_type == PT_LOAD) | |
887badb3 RM |
89 | { |
90 | bfd_boolean executable = segment_executable (seg); | |
91 | ||
92 | if (executable | |
93 | && seg->count > 0 | |
94 | && seg->sections[0]->vma % minpagesize == 0) | |
95 | { | |
96 | asection *lastsec = seg->sections[seg->count - 1]; | |
97 | bfd_vma end = lastsec->vma + lastsec->size; | |
98 | if (end % minpagesize != 0) | |
99 | { | |
100 | /* This is an executable segment that starts on a page | |
101 | boundary but does not end on a page boundary. Fill | |
102 | it out to a whole page with code fill (the tail of | |
103 | the segment will not be within any section). Thus | |
104 | the entire code segment can be mapped from the file | |
105 | as whole pages and that mapping will contain only | |
106 | valid instructions. | |
107 | ||
108 | To accomplish this, we must fake out the code in | |
109 | assign_file_positions_for_load_sections (elf.c) so | |
110 | that it advances past the rest of the final page, | |
111 | rather than trying to put the next (unaligned, or | |
112 | unallocated) section. We do this by appending a | |
113 | dummy section record to this element in the segment | |
114 | map. No such output section ever actually exists, | |
115 | but this gets the layout logic to advance the file | |
116 | positions past this partial page. Since we are | |
117 | lying to BFD like this, nothing will ever know to | |
118 | write the section contents. So we do that by hand | |
119 | after the fact, in nacl_final_write_processing, below. */ | |
120 | ||
121 | struct elf_segment_map *newseg; | |
122 | asection *sec; | |
123 | struct bfd_elf_section_data *secdata; | |
124 | ||
125 | BFD_ASSERT (!seg->p_size_valid); | |
126 | ||
127 | secdata = bfd_zalloc (abfd, sizeof *secdata); | |
128 | if (secdata == NULL) | |
129 | return FALSE; | |
130 | ||
131 | sec = bfd_zalloc (abfd, sizeof *sec); | |
132 | if (sec == NULL) | |
133 | return FALSE; | |
134 | ||
135 | /* Fill in only the fields that actually affect the logic | |
136 | in assign_file_positions_for_load_sections. */ | |
137 | sec->vma = end; | |
138 | sec->lma = lastsec->lma + lastsec->size; | |
139 | sec->size = minpagesize - (end % minpagesize); | |
140 | sec->flags = (SEC_ALLOC | SEC_LOAD | |
141 | | SEC_READONLY | SEC_CODE | SEC_LINKER_CREATED); | |
142 | sec->used_by_bfd = secdata; | |
143 | ||
144 | secdata->this_hdr.sh_type = SHT_PROGBITS; | |
145 | secdata->this_hdr.sh_flags = SHF_ALLOC | SHF_EXECINSTR; | |
146 | secdata->this_hdr.sh_addr = sec->vma; | |
147 | secdata->this_hdr.sh_size = sec->size; | |
148 | ||
149 | newseg = bfd_alloc (abfd, | |
150 | sizeof *newseg + ((seg->count + 1) | |
151 | * sizeof (asection *))); | |
152 | if (newseg == NULL) | |
153 | return FALSE; | |
154 | memcpy (newseg, seg, | |
155 | sizeof *newseg + (seg->count * sizeof (asection *))); | |
156 | newseg->sections[newseg->count++] = sec; | |
157 | *m = seg = newseg; | |
158 | } | |
159 | } | |
160 | ||
161 | /* First, we're just finding the earliest PT_LOAD. | |
162 | By the normal rules, this will be the lowest-addressed one. | |
163 | We only have anything interesting to do if it's executable. */ | |
164 | last_load = m; | |
165 | if (first_load == NULL) | |
166 | { | |
167 | if (!executable) | |
168 | goto next; | |
169 | first_load = m; | |
170 | } | |
171 | /* Now that we've noted the first PT_LOAD, we're looking for | |
172 | the first non-executable PT_LOAD with a nonempty p_filesz. */ | |
173 | else if (!moved_headers | |
174 | && segment_eligible_for_headers (seg, minpagesize, | |
175 | sizeof_headers)) | |
176 | { | |
177 | /* This is the one we were looking for! | |
178 | ||
179 | First, clear the flags on previous segments that | |
180 | say they include the file header and phdrs. */ | |
181 | struct elf_segment_map *prevseg; | |
182 | for (prevseg = *first_load; | |
183 | prevseg != seg; | |
184 | prevseg = prevseg->next) | |
185 | if (prevseg->p_type == PT_LOAD) | |
186 | { | |
187 | prevseg->includes_filehdr = 0; | |
188 | prevseg->includes_phdrs = 0; | |
189 | } | |
190 | ||
191 | /* This segment will include those headers instead. */ | |
192 | seg->includes_filehdr = 1; | |
193 | seg->includes_phdrs = 1; | |
194 | ||
195 | moved_headers = TRUE; | |
196 | } | |
197 | } | |
198 | ||
199 | next: | |
5a68afcf RM |
200 | m = &seg->next; |
201 | } | |
202 | ||
203 | if (first_load != last_load && moved_headers) | |
204 | { | |
205 | /* Now swap the first and last PT_LOAD segments' | |
887badb3 | 206 | positions in segment_map. */ |
5a68afcf RM |
207 | struct elf_segment_map *first = *first_load; |
208 | struct elf_segment_map *last = *last_load; | |
209 | *first_load = first->next; | |
210 | first->next = last->next; | |
211 | last->next = first; | |
212 | } | |
213 | ||
214 | return TRUE; | |
215 | } | |
216 | ||
217 | /* After nacl_modify_segment_map has done its work, the file layout has | |
218 | been done as we wanted. But the PT_LOAD phdrs are no longer in the | |
219 | proper order for the ELF rule that they must appear in ascending address | |
220 | order. So find the two segments we swapped before, and swap them back. */ | |
221 | bfd_boolean | |
aa6407c6 | 222 | nacl_modify_program_headers (bfd *abfd, struct bfd_link_info *info) |
5a68afcf | 223 | { |
12bd6957 | 224 | struct elf_segment_map **m = &elf_seg_map (abfd); |
5a68afcf RM |
225 | Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr; |
226 | Elf_Internal_Phdr *p = phdr; | |
227 | ||
d324f6d6 RM |
228 | if (info != NULL && info->user_phdrs) |
229 | /* The linker script used PHDRS explicitly, so don't change what the | |
230 | user asked for. */ | |
231 | return TRUE; | |
232 | ||
5a68afcf RM |
233 | /* Find the PT_LOAD that contains the headers (should be the first). */ |
234 | while (*m != NULL) | |
235 | { | |
236 | if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr) | |
887badb3 | 237 | break; |
5a68afcf RM |
238 | |
239 | m = &(*m)->next; | |
240 | ++p; | |
241 | } | |
242 | ||
243 | if (*m != NULL) | |
244 | { | |
245 | struct elf_segment_map **first_load_seg = m; | |
246 | Elf_Internal_Phdr *first_load_phdr = p; | |
247 | struct elf_segment_map **next_load_seg = NULL; | |
248 | Elf_Internal_Phdr *next_load_phdr = NULL; | |
249 | ||
250 | /* Now move past that first one and find the PT_LOAD that should be | |
887badb3 | 251 | before it by address order. */ |
5a68afcf RM |
252 | |
253 | m = &(*m)->next; | |
254 | ++p; | |
255 | ||
887badb3 RM |
256 | while (*m != NULL) |
257 | { | |
258 | if (p->p_type == PT_LOAD && p->p_vaddr < first_load_phdr->p_vaddr) | |
259 | { | |
260 | next_load_seg = m; | |
261 | next_load_phdr = p; | |
262 | break; | |
263 | } | |
5a68afcf | 264 | |
887badb3 RM |
265 | m = &(*m)->next; |
266 | ++p; | |
267 | } | |
5a68afcf RM |
268 | |
269 | /* Swap their positions in the segment_map back to how they used to be. | |
887badb3 RM |
270 | The phdrs have already been set up by now, so we have to slide up |
271 | the earlier ones to insert the one that should be first. */ | |
5a68afcf | 272 | if (next_load_seg != NULL) |
887badb3 RM |
273 | { |
274 | Elf_Internal_Phdr move_phdr; | |
275 | struct elf_segment_map *first_seg = *first_load_seg; | |
276 | struct elf_segment_map *next_seg = *next_load_seg; | |
277 | struct elf_segment_map *first_next = first_seg->next; | |
278 | struct elf_segment_map *next_next = next_seg->next; | |
279 | ||
280 | if (next_load_seg == &first_seg->next) | |
281 | { | |
282 | *first_load_seg = next_seg; | |
283 | next_seg->next = first_seg; | |
284 | first_seg->next = next_next; | |
285 | } | |
286 | else | |
287 | { | |
288 | *first_load_seg = first_next; | |
289 | *next_load_seg = next_next; | |
290 | ||
291 | first_seg->next = *next_load_seg; | |
292 | *next_load_seg = first_seg; | |
293 | ||
294 | next_seg->next = *first_load_seg; | |
295 | *first_load_seg = next_seg; | |
296 | } | |
297 | ||
298 | move_phdr = *next_load_phdr; | |
299 | memmove (first_load_phdr + 1, first_load_phdr, | |
300 | (next_load_phdr - first_load_phdr) * sizeof move_phdr); | |
301 | *first_load_phdr = move_phdr; | |
302 | } | |
5a68afcf RM |
303 | } |
304 | ||
305 | return TRUE; | |
306 | } | |
887badb3 RM |
307 | |
308 | void | |
309 | nacl_final_write_processing (bfd *abfd, bfd_boolean linker ATTRIBUTE_UNUSED) | |
310 | { | |
311 | struct elf_segment_map *seg; | |
312 | for (seg = elf_seg_map (abfd); seg != NULL; seg = seg->next) | |
313 | if (seg->p_type == PT_LOAD | |
314 | && seg->count > 1 | |
315 | && seg->sections[seg->count - 1]->owner == NULL) | |
316 | { | |
317 | /* This is a fake section added in nacl_modify_segment_map, above. | |
318 | It's not a real BFD section, so nothing wrote its contents. | |
319 | Now write out its contents. */ | |
320 | ||
321 | asection *sec = seg->sections[seg->count - 1]; | |
322 | char *fill; | |
323 | ||
324 | BFD_ASSERT (sec->flags & SEC_LINKER_CREATED); | |
325 | BFD_ASSERT (sec->flags & SEC_CODE); | |
326 | BFD_ASSERT (sec->size > 0); | |
327 | ||
328 | fill = abfd->arch_info->fill (sec->size, bfd_big_endian (abfd), TRUE); | |
329 | ||
330 | if (fill == NULL | |
331 | || bfd_seek (abfd, sec->filepos, SEEK_SET) != 0 | |
332 | || bfd_bwrite (fill, sec->size, abfd) != sec->size) | |
333 | { | |
334 | /* We don't have a proper way to report an error here. So | |
335 | instead fudge things so that elf_write_shdrs_and_ehdr will | |
336 | fail. */ | |
337 | elf_elfheader (abfd)->e_shoff = (file_ptr) -1; | |
338 | } | |
339 | ||
340 | free (fill); | |
341 | } | |
342 | } |