354 lines
11 KiB
C
354 lines
11 KiB
C
/* Native Client support for ELF
|
|
Copyright (C) 2012-2015 Free Software Foundation, Inc.
|
|
|
|
This file is part of BFD, the Binary File Descriptor library.
|
|
|
|
This program is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 3 of the License, or
|
|
(at your option) any later version.
|
|
|
|
This program is distributed in the hope that it will be useful,
|
|
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
GNU General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with this program. If not, see <http://www.gnu.org/licenses/>. */
|
|
|
|
#include "sysdep.h"
|
|
#include "bfd.h"
|
|
#include "libbfd.h"
|
|
#include "elf-bfd.h"
|
|
#include "elf-nacl.h"
|
|
#include "elf/common.h"
|
|
#include "elf/internal.h"
|
|
|
|
static bfd_boolean
|
|
segment_executable (struct elf_segment_map *seg)
|
|
{
|
|
if (seg->p_flags_valid)
|
|
return (seg->p_flags & PF_X) != 0;
|
|
else
|
|
{
|
|
/* The p_flags value has not been computed yet,
|
|
so we have to look through the sections. */
|
|
unsigned int i;
|
|
for (i = 0; i < seg->count; ++i)
|
|
if (seg->sections[i]->flags & SEC_CODE)
|
|
return TRUE;
|
|
}
|
|
return FALSE;
|
|
}
|
|
|
|
/* Determine if this segment is eligible to receive the file and program
|
|
headers. It must be read-only and non-executable.
|
|
Its first section must start far enough past the page boundary to
|
|
allow space for the headers. */
|
|
static bfd_boolean
|
|
segment_eligible_for_headers (struct elf_segment_map *seg,
|
|
bfd_vma minpagesize, bfd_vma sizeof_headers)
|
|
{
|
|
unsigned int i;
|
|
if (seg->count == 0 || seg->sections[0]->lma % minpagesize < sizeof_headers)
|
|
return FALSE;
|
|
for (i = 0; i < seg->count; ++i)
|
|
{
|
|
if ((seg->sections[i]->flags & (SEC_CODE|SEC_READONLY)) != SEC_READONLY)
|
|
return FALSE;
|
|
}
|
|
return TRUE;
|
|
}
|
|
|
|
|
|
/* We permute the segment_map to get BFD to do the file layout we want:
|
|
The first non-executable PT_LOAD segment appears first in the file
|
|
and contains the ELF file header and phdrs. */
|
|
bfd_boolean
|
|
nacl_modify_segment_map (bfd *abfd, struct bfd_link_info *info)
|
|
{
|
|
const struct elf_backend_data *const bed = get_elf_backend_data (abfd);
|
|
struct elf_segment_map **m = &elf_seg_map (abfd);
|
|
struct elf_segment_map **first_load = NULL;
|
|
struct elf_segment_map **last_load = NULL;
|
|
bfd_boolean moved_headers = FALSE;
|
|
int sizeof_headers;
|
|
|
|
if (info != NULL && info->user_phdrs)
|
|
/* The linker script used PHDRS explicitly, so don't change what the
|
|
user asked for. */
|
|
return TRUE;
|
|
|
|
if (info != NULL)
|
|
/* We're doing linking, so evalute SIZEOF_HEADERS as in a linker script. */
|
|
sizeof_headers = bfd_sizeof_headers (abfd, info);
|
|
else
|
|
{
|
|
/* We're not doing linking, so this is objcopy or suchlike.
|
|
We just need to collect the size of the existing headers. */
|
|
struct elf_segment_map *seg;
|
|
sizeof_headers = bed->s->sizeof_ehdr;
|
|
for (seg = *m; seg != NULL; seg = seg->next)
|
|
sizeof_headers += bed->s->sizeof_phdr;
|
|
}
|
|
|
|
while (*m != NULL)
|
|
{
|
|
struct elf_segment_map *seg = *m;
|
|
|
|
if (seg->p_type == PT_LOAD)
|
|
{
|
|
bfd_boolean executable = segment_executable (seg);
|
|
|
|
if (executable
|
|
&& seg->count > 0
|
|
&& seg->sections[0]->vma % bed->minpagesize == 0)
|
|
{
|
|
asection *lastsec = seg->sections[seg->count - 1];
|
|
bfd_vma end = lastsec->vma + lastsec->size;
|
|
if (end % bed->minpagesize != 0)
|
|
{
|
|
/* This is an executable segment that starts on a page
|
|
boundary but does not end on a page boundary. Fill
|
|
it out to a whole page with code fill (the tail of
|
|
the segment will not be within any section). Thus
|
|
the entire code segment can be mapped from the file
|
|
as whole pages and that mapping will contain only
|
|
valid instructions.
|
|
|
|
To accomplish this, we must fake out the code in
|
|
assign_file_positions_for_load_sections (elf.c) so
|
|
that it advances past the rest of the final page,
|
|
rather than trying to put the next (unaligned, or
|
|
unallocated) section. We do this by appending a
|
|
dummy section record to this element in the segment
|
|
map. No such output section ever actually exists,
|
|
but this gets the layout logic to advance the file
|
|
positions past this partial page. Since we are
|
|
lying to BFD like this, nothing will ever know to
|
|
write the section contents. So we do that by hand
|
|
after the fact, in nacl_final_write_processing, below. */
|
|
|
|
struct elf_segment_map *newseg;
|
|
asection *sec;
|
|
struct bfd_elf_section_data *secdata;
|
|
|
|
BFD_ASSERT (!seg->p_size_valid);
|
|
|
|
secdata = bfd_zalloc (abfd, sizeof *secdata);
|
|
if (secdata == NULL)
|
|
return FALSE;
|
|
|
|
sec = bfd_zalloc (abfd, sizeof *sec);
|
|
if (sec == NULL)
|
|
return FALSE;
|
|
|
|
/* Fill in only the fields that actually affect the logic
|
|
in assign_file_positions_for_load_sections. */
|
|
sec->vma = end;
|
|
sec->lma = lastsec->lma + lastsec->size;
|
|
sec->size = bed->minpagesize - (end % bed->minpagesize);
|
|
sec->flags = (SEC_ALLOC | SEC_LOAD
|
|
| SEC_READONLY | SEC_CODE | SEC_LINKER_CREATED);
|
|
sec->used_by_bfd = secdata;
|
|
|
|
secdata->this_hdr.sh_type = SHT_PROGBITS;
|
|
secdata->this_hdr.sh_flags = SHF_ALLOC | SHF_EXECINSTR;
|
|
secdata->this_hdr.sh_addr = sec->vma;
|
|
secdata->this_hdr.sh_size = sec->size;
|
|
|
|
newseg = bfd_alloc (abfd,
|
|
sizeof *newseg + ((seg->count + 1)
|
|
* sizeof (asection *)));
|
|
if (newseg == NULL)
|
|
return FALSE;
|
|
memcpy (newseg, seg,
|
|
sizeof *newseg + (seg->count * sizeof (asection *)));
|
|
newseg->sections[newseg->count++] = sec;
|
|
*m = seg = newseg;
|
|
}
|
|
}
|
|
|
|
/* First, we're just finding the earliest PT_LOAD.
|
|
By the normal rules, this will be the lowest-addressed one.
|
|
We only have anything interesting to do if it's executable. */
|
|
last_load = m;
|
|
if (first_load == NULL)
|
|
{
|
|
if (!executable)
|
|
goto next;
|
|
first_load = m;
|
|
}
|
|
/* Now that we've noted the first PT_LOAD, we're looking for
|
|
the first non-executable PT_LOAD with a nonempty p_filesz. */
|
|
else if (!moved_headers
|
|
&& segment_eligible_for_headers (seg, bed->minpagesize,
|
|
sizeof_headers))
|
|
{
|
|
/* This is the one we were looking for!
|
|
|
|
First, clear the flags on previous segments that
|
|
say they include the file header and phdrs. */
|
|
struct elf_segment_map *prevseg;
|
|
for (prevseg = *first_load;
|
|
prevseg != seg;
|
|
prevseg = prevseg->next)
|
|
if (prevseg->p_type == PT_LOAD)
|
|
{
|
|
prevseg->includes_filehdr = 0;
|
|
prevseg->includes_phdrs = 0;
|
|
}
|
|
|
|
/* This segment will include those headers instead. */
|
|
seg->includes_filehdr = 1;
|
|
seg->includes_phdrs = 1;
|
|
|
|
moved_headers = TRUE;
|
|
}
|
|
}
|
|
|
|
next:
|
|
m = &seg->next;
|
|
}
|
|
|
|
if (first_load != last_load && moved_headers)
|
|
{
|
|
/* Now swap the first and last PT_LOAD segments'
|
|
positions in segment_map. */
|
|
struct elf_segment_map *first = *first_load;
|
|
struct elf_segment_map *last = *last_load;
|
|
*first_load = first->next;
|
|
first->next = last->next;
|
|
last->next = first;
|
|
}
|
|
|
|
return TRUE;
|
|
}
|
|
|
|
/* After nacl_modify_segment_map has done its work, the file layout has
|
|
been done as we wanted. But the PT_LOAD phdrs are no longer in the
|
|
proper order for the ELF rule that they must appear in ascending address
|
|
order. So find the two segments we swapped before, and swap them back. */
|
|
bfd_boolean
|
|
nacl_modify_program_headers (bfd *abfd, struct bfd_link_info *info)
|
|
{
|
|
struct elf_segment_map **m = &elf_seg_map (abfd);
|
|
Elf_Internal_Phdr *phdr = elf_tdata (abfd)->phdr;
|
|
Elf_Internal_Phdr *p = phdr;
|
|
|
|
if (info != NULL && info->user_phdrs)
|
|
/* The linker script used PHDRS explicitly, so don't change what the
|
|
user asked for. */
|
|
return TRUE;
|
|
|
|
/* Find the PT_LOAD that contains the headers (should be the first). */
|
|
while (*m != NULL)
|
|
{
|
|
if ((*m)->p_type == PT_LOAD && (*m)->includes_filehdr)
|
|
break;
|
|
|
|
m = &(*m)->next;
|
|
++p;
|
|
}
|
|
|
|
if (*m != NULL)
|
|
{
|
|
struct elf_segment_map **first_load_seg = m;
|
|
Elf_Internal_Phdr *first_load_phdr = p;
|
|
struct elf_segment_map **next_load_seg = NULL;
|
|
Elf_Internal_Phdr *next_load_phdr = NULL;
|
|
|
|
/* Now move past that first one and find the PT_LOAD that should be
|
|
before it by address order. */
|
|
|
|
m = &(*m)->next;
|
|
++p;
|
|
|
|
while (*m != NULL)
|
|
{
|
|
if (p->p_type == PT_LOAD && p->p_vaddr < first_load_phdr->p_vaddr)
|
|
{
|
|
next_load_seg = m;
|
|
next_load_phdr = p;
|
|
break;
|
|
}
|
|
|
|
m = &(*m)->next;
|
|
++p;
|
|
}
|
|
|
|
/* Swap their positions in the segment_map back to how they used to be.
|
|
The phdrs have already been set up by now, so we have to slide up
|
|
the earlier ones to insert the one that should be first. */
|
|
if (next_load_seg != NULL)
|
|
{
|
|
Elf_Internal_Phdr move_phdr;
|
|
struct elf_segment_map *first_seg = *first_load_seg;
|
|
struct elf_segment_map *next_seg = *next_load_seg;
|
|
struct elf_segment_map *first_next = first_seg->next;
|
|
struct elf_segment_map *next_next = next_seg->next;
|
|
|
|
if (next_load_seg == &first_seg->next)
|
|
{
|
|
*first_load_seg = next_seg;
|
|
next_seg->next = first_seg;
|
|
first_seg->next = next_next;
|
|
}
|
|
else
|
|
{
|
|
*first_load_seg = first_next;
|
|
*next_load_seg = next_next;
|
|
|
|
first_seg->next = *next_load_seg;
|
|
*next_load_seg = first_seg;
|
|
|
|
next_seg->next = *first_load_seg;
|
|
*first_load_seg = next_seg;
|
|
}
|
|
|
|
move_phdr = *next_load_phdr;
|
|
memmove (first_load_phdr + 1, first_load_phdr,
|
|
(next_load_phdr - first_load_phdr) * sizeof move_phdr);
|
|
*first_load_phdr = move_phdr;
|
|
}
|
|
}
|
|
|
|
return TRUE;
|
|
}
|
|
|
|
void
|
|
nacl_final_write_processing (bfd *abfd, bfd_boolean linker ATTRIBUTE_UNUSED)
|
|
{
|
|
struct elf_segment_map *seg;
|
|
for (seg = elf_seg_map (abfd); seg != NULL; seg = seg->next)
|
|
if (seg->p_type == PT_LOAD
|
|
&& seg->count > 1
|
|
&& seg->sections[seg->count - 1]->owner == NULL)
|
|
{
|
|
/* This is a fake section added in nacl_modify_segment_map, above.
|
|
It's not a real BFD section, so nothing wrote its contents.
|
|
Now write out its contents. */
|
|
|
|
asection *sec = seg->sections[seg->count - 1];
|
|
char *fill;
|
|
|
|
BFD_ASSERT (sec->flags & SEC_LINKER_CREATED);
|
|
BFD_ASSERT (sec->flags & SEC_CODE);
|
|
BFD_ASSERT (sec->size > 0);
|
|
|
|
fill = abfd->arch_info->fill (sec->size, bfd_big_endian (abfd), TRUE);
|
|
|
|
if (fill == NULL
|
|
|| bfd_seek (abfd, sec->filepos, SEEK_SET) != 0
|
|
|| bfd_bwrite (fill, sec->size, abfd) != sec->size)
|
|
{
|
|
/* We don't have a proper way to report an error here. So
|
|
instead fudge things so that elf_write_shdrs_and_ehdr will
|
|
fail. */
|
|
elf_elfheader (abfd)->e_shoff = (file_ptr) -1;
|
|
}
|
|
|
|
free (fill);
|
|
}
|
|
}
|