225 lines
7.3 KiB
C
225 lines
7.3 KiB
C
/* Native Client support for ELF
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Copyright 2012 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, write to the Free Software
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Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "sysdep.h"
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#include "bfd.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 bfd_boolean
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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 non-executable and have contents. Its first
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section must start far enough past the page boundary to allow space
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for the headers. */
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static bfd_boolean
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segment_eligible_for_headers (struct elf_segment_map *seg,
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bfd_vma maxpagesize, bfd_vma sizeof_headers)
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{
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bfd_boolean any_contents = FALSE;
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unsigned int i;
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if (seg->count == 0 || seg->sections[0]->lma % maxpagesize < 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)
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return FALSE;
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if (seg->sections[i]->flags & SEC_HAS_CONTENTS)
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any_contents = TRUE;
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}
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return any_contents;
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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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bfd_boolean
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nacl_modify_segment_map (bfd *abfd, struct bfd_link_info *info)
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{
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struct elf_segment_map **m = &elf_tdata (abfd)->segment_map;
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struct elf_segment_map **first_load = NULL;
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struct elf_segment_map **last_load = NULL;
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bfd_boolean moved_headers = FALSE;
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int sizeof_headers = info == NULL ? 0 : bfd_sizeof_headers (abfd, info);
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bfd_vma maxpagesize = get_elf_backend_data (abfd)->maxpagesize;
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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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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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/* 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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We only have anything interesting to do if it's executable. */
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last_load = m;
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if (first_load == NULL)
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{
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if (!segment_executable (*m))
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return TRUE;
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first_load = m;
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}
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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 (!moved_headers
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&& segment_eligible_for_headers (seg, maxpagesize,
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sizeof_headers))
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{
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/* This is the one we were looking for!
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First, clear the flags on previous segments that
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say they include the file header and phdrs. */
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struct elf_segment_map *prevseg;
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for (prevseg = *first_load;
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prevseg != seg;
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prevseg = prevseg->next)
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if (prevseg->p_type == PT_LOAD)
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{
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prevseg->includes_filehdr = 0;
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prevseg->includes_phdrs = 0;
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}
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/* This segment will include those headers instead. */
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seg->includes_filehdr = 1;
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seg->includes_phdrs = 1;
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moved_headers = TRUE;
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}
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}
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m = &seg->next;
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}
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if (first_load != last_load && moved_headers)
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{
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/* Now swap the first and last PT_LOAD segments'
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positions in segment_map. */
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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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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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bfd_boolean
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nacl_modify_program_headers (bfd *abfd, struct bfd_link_info *info)
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{
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struct elf_segment_map **m = &elf_tdata (abfd)->segment_map;
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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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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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/* 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 used to be.
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The phdrs have already been set up by now, so we have to slide up
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the earlier ones to insert the one 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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first_seg->next = next_next;
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*first_load_seg = next_seg;
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next_seg->next = first_next;
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*next_load_seg = first_seg;
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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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return TRUE;
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}
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