363 lines
11 KiB
C
363 lines
11 KiB
C
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/* Native Client support for ELF
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Copyright (C) 2012-2022 Free Software Foundation, Inc.
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This file is part of BFD, the Binary File Descriptor library.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include "sysdep.h"
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#include "bfd.h"
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#include "libbfd.h"
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#include "elf-bfd.h"
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#include "elf-nacl.h"
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#include "elf/common.h"
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#include "elf/internal.h"
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static bool
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segment_executable (struct elf_segment_map *seg)
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{
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if (seg->p_flags_valid)
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return (seg->p_flags & PF_X) != 0;
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else
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{
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/* The p_flags value has not been computed yet,
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so we have to look through the sections. */
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unsigned int i;
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for (i = 0; i < seg->count; ++i)
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if (seg->sections[i]->flags & SEC_CODE)
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return true;
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}
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return false;
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}
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/* Determine if this segment is eligible to receive the file and program
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headers. It must be read-only and non-executable.
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Its first section must start far enough past the page boundary to
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allow space for the headers. */
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static bool
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segment_eligible_for_headers (struct elf_segment_map *seg,
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bfd_vma minpagesize, bfd_vma sizeof_headers)
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{
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unsigned int i;
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if (seg->count == 0 || seg->sections[0]->lma % minpagesize < sizeof_headers)
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return false;
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for (i = 0; i < seg->count; ++i)
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{
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if ((seg->sections[i]->flags & (SEC_CODE|SEC_READONLY)) != SEC_READONLY)
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return false;
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}
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return true;
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}
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/* We permute the segment_map to get BFD to do the file layout we want:
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The first non-executable PT_LOAD segment appears first in the file
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and contains the ELF file header and phdrs. */
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bool
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nacl_modify_segment_map (bfd *abfd, struct bfd_link_info *info)
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{
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const struct elf_backend_data *const bed = get_elf_backend_data (abfd);
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struct elf_segment_map **m = &elf_seg_map (abfd);
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struct elf_segment_map **first_load = NULL;
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struct elf_segment_map **headers = NULL;
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int sizeof_headers;
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if (info != NULL && info->user_phdrs)
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/* The linker script used PHDRS explicitly, so don't change what the
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user asked for. */
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return true;
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if (info != NULL)
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/* We're doing linking, so evalute SIZEOF_HEADERS as in a linker script. */
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sizeof_headers = bfd_sizeof_headers (abfd, info);
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else
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{
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/* We're not doing linking, so this is objcopy or suchlike.
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We just need to collect the size of the existing headers. */
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struct elf_segment_map *seg;
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sizeof_headers = bed->s->sizeof_ehdr;
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for (seg = *m; seg != NULL; seg = seg->next)
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sizeof_headers += bed->s->sizeof_phdr;
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}
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while (*m != NULL)
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{
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struct elf_segment_map *seg = *m;
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if (seg->p_type == PT_LOAD)
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{
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bool executable = segment_executable (seg);
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if (executable
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&& seg->count > 0
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&& seg->sections[0]->vma % bed->minpagesize == 0)
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{
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asection *lastsec = seg->sections[seg->count - 1];
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bfd_vma end = lastsec->vma + lastsec->size;
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if (end % bed->minpagesize != 0)
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{
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/* This is an executable segment that starts on a page
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boundary but does not end on a page boundary. Fill
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it out to a whole page with code fill (the tail of
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the segment will not be within any section). Thus
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the entire code segment can be mapped from the file
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as whole pages and that mapping will contain only
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valid instructions.
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To accomplish this, we must fake out the code in
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assign_file_positions_for_load_sections (elf.c) so
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that it advances past the rest of the final page,
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rather than trying to put the next (unaligned, or
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unallocated) section. We do this by appending a
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dummy section record to this element in the segment
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map. No such output section ever actually exists,
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but this gets the layout logic to advance the file
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positions past this partial page. Since we are
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lying to BFD like this, nothing will ever know to
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write the section contents. So we do that by hand
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after the fact, in nacl_final_write_processing, below. */
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struct elf_segment_map *newseg;
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asection *sec;
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struct bfd_elf_section_data *secdata;
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BFD_ASSERT (!seg->p_size_valid);
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secdata = bfd_zalloc (abfd, sizeof *secdata);
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if (secdata == NULL)
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return false;
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sec = bfd_zalloc (abfd, sizeof *sec);
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if (sec == NULL)
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return false;
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/* Fill in only the fields that actually affect the logic
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in assign_file_positions_for_load_sections. */
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sec->vma = end;
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sec->lma = lastsec->lma + lastsec->size;
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sec->size = bed->minpagesize - (end % bed->minpagesize);
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sec->flags = (SEC_ALLOC | SEC_LOAD
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| SEC_READONLY | SEC_CODE | SEC_LINKER_CREATED);
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sec->used_by_bfd = secdata;
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secdata->this_hdr.sh_type = SHT_PROGBITS;
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secdata->this_hdr.sh_flags = SHF_ALLOC | SHF_EXECINSTR;
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secdata->this_hdr.sh_addr = sec->vma;
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secdata->this_hdr.sh_size = sec->size;
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newseg
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= bfd_alloc (abfd, (sizeof (*newseg)
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+ seg->count * sizeof (asection *)));
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if (newseg == NULL)
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return false;
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memcpy (newseg, seg, (sizeof (*newseg) - sizeof (asection *)
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+ seg->count * sizeof (asection *)));
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newseg->sections[newseg->count++] = sec;
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*m = seg = newseg;
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}
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}
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/* First, we're just finding the earliest PT_LOAD.
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By the normal rules, this will be the lowest-addressed one. */
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if (first_load == NULL)
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first_load = m;
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/* Now that we've noted the first PT_LOAD, we're looking for
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the first non-executable PT_LOAD with a nonempty p_filesz. */
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else if (headers == NULL
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&& segment_eligible_for_headers (seg, bed->minpagesize,
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sizeof_headers))
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headers = m;
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}
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m = &seg->next;
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}
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if (headers != NULL)
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{
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struct elf_segment_map **last_load = NULL;
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struct elf_segment_map *seg;
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m = first_load;
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while ((seg = *m) != NULL)
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{
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if (seg->p_type == PT_LOAD)
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{
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/* Clear the flags on any previous segment that
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included the file header and phdrs. */
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seg->includes_filehdr = 0;
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seg->includes_phdrs = 0;
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seg->no_sort_lma = 1;
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/* Also strip out empty segments. */
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if (seg->count == 0)
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{
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if (headers == &seg->next)
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headers = m;
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*m = seg->next;
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continue;
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}
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last_load = m;
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}
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m = &seg->next;
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}
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/* This segment will include those headers instead. */
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seg = *headers;
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seg->includes_filehdr = 1;
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seg->includes_phdrs = 1;
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if (last_load != NULL && first_load != last_load && first_load != headers)
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{
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/* Put the first PT_LOAD header last. */
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struct elf_segment_map *first = *first_load;
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struct elf_segment_map *last = *last_load;
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*first_load = first->next;
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first->next = last->next;
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last->next = first;
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}
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}
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return true;
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}
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/* After nacl_modify_segment_map has done its work, the file layout has
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been done as we wanted. But the PT_LOAD phdrs are no longer in the
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proper order for the ELF rule that they must appear in ascending address
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order. So find the two segments we swapped before, and swap them back. */
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bool
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nacl_modify_headers (bfd *abfd, struct bfd_link_info *info)
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{
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if (info != NULL && info->user_phdrs)
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/* The linker script used PHDRS explicitly, so don't change what the
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user asked for. */
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;
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else
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{
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struct elf_segment_map **m = &elf_seg_map (abfd);
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Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr;
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Elf_Internal_Phdr *p = phdr;
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/* Find the PT_LOAD that contains the headers (should be the first). */
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while (*m != NULL)
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{
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if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr)
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break;
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m = &(*m)->next;
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++p;
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}
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if (*m != NULL)
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{
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struct elf_segment_map **first_load_seg = m;
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Elf_Internal_Phdr *first_load_phdr = p;
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struct elf_segment_map **next_load_seg = NULL;
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Elf_Internal_Phdr *next_load_phdr = NULL;
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/* Now move past that first one and find the PT_LOAD that should be
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before it by address order. */
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m = &(*m)->next;
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++p;
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while (*m != NULL)
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{
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if (p->p_type == PT_LOAD && p->p_vaddr < first_load_phdr->p_vaddr)
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{
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next_load_seg = m;
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next_load_phdr = p;
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break;
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}
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m = &(*m)->next;
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++p;
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}
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/* Swap their positions in the segment_map back to how they
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used to be. The phdrs have already been set up by now,
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so we have to slide up the earlier ones to insert the one
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that should be first. */
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if (next_load_seg != NULL)
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{
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Elf_Internal_Phdr move_phdr;
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struct elf_segment_map *first_seg = *first_load_seg;
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struct elf_segment_map *next_seg = *next_load_seg;
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struct elf_segment_map *first_next = first_seg->next;
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struct elf_segment_map *next_next = next_seg->next;
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if (next_load_seg == &first_seg->next)
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{
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*first_load_seg = next_seg;
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next_seg->next = first_seg;
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first_seg->next = next_next;
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}
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else
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{
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*first_load_seg = first_next;
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*next_load_seg = next_next;
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first_seg->next = *next_load_seg;
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*next_load_seg = first_seg;
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next_seg->next = *first_load_seg;
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*first_load_seg = next_seg;
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}
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move_phdr = *next_load_phdr;
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memmove (first_load_phdr + 1, first_load_phdr,
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(next_load_phdr - first_load_phdr) * sizeof move_phdr);
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*first_load_phdr = move_phdr;
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}
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}
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}
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return _bfd_elf_modify_headers (abfd, info);
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}
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bool
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nacl_final_write_processing (bfd *abfd)
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{
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struct elf_segment_map *seg;
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for (seg = elf_seg_map (abfd); seg != NULL; seg = seg->next)
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if (seg->p_type == PT_LOAD
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&& seg->count > 1
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&& seg->sections[seg->count - 1]->owner == NULL)
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{
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/* This is a fake section added in nacl_modify_segment_map, above.
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It's not a real BFD section, so nothing wrote its contents.
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Now write out its contents. */
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asection *sec = seg->sections[seg->count - 1];
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char *fill;
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BFD_ASSERT (sec->flags & SEC_LINKER_CREATED);
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BFD_ASSERT (sec->flags & SEC_CODE);
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BFD_ASSERT (sec->size > 0);
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fill = abfd->arch_info->fill (sec->size, bfd_big_endian (abfd), true);
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if (fill == NULL
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|| bfd_seek (abfd, sec->filepos, SEEK_SET) != 0
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|| bfd_bwrite (fill, sec->size, abfd) != sec->size)
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{
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/* We don't have a proper way to report an error here. So
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instead fudge things so that elf_write_shdrs_and_ehdr will
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fail. */
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elf_elfheader (abfd)->e_shoff = (file_ptr) -1;
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}
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free (fill);
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}
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return _bfd_elf_final_write_processing (abfd);
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}
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