ld: Allow section groups to be resolved as part of a relocatable link
This commit adds a new linker feature: the ability to resolve section groups as part of a relocatable link. Currently section groups are automatically resolved when performing a final link, and are carried through when performing a relocatable link. By carried through this means that one copy of each section group (from all the copies that might be found in all the input files) is placed into the output file. Sections that are part of a section group will not match input section specifiers within a linker script and are forcibly kept as separate sections. There is a slight resemblance between section groups and common section. Like section groups, common sections are carried through when performing a relocatable link, and resolved (allocated actual space) only at final link time. However, with common sections there is an ability to force the linker to allocate space for the common sections when performing a relocatable link, there's currently no such ability for section groups. This commit adds such a mechanism. This new facility can be accessed in two ways, first there's a command line switch --force-group-allocation, second, there's a new linker script command FORCE_GROUP_ALLOCATION. If one of these is used when performing a relocatable link then the linker will resolve the section groups as though it were performing a final link, the section group will be deleted, and the members of the group will be placed like normal input sections. If there are multiple copies of the group (from multiple input files) then only one copy of the group members will be placed, the duplicate copies will be discarded. Unlike common sections that have the --no-define-common command line flag, and INHIBIT_COMMON_ALLOCATION linker script command there is no way to prevent group resolution during a final link, this is because the ELF gABI specifically prohibits the presence of SHT_GROUP sections in a fully linked executable. However, the code as written should make adding such a feature trivial, setting the new resolve_section_groups flag to false during a final link should work as you'd expect. bfd/ChangeLog: * elf.c (_bfd_elf_make_section_from_shdr): Don't initially mark SEC_GROUP sections as SEC_EXCLUDE. (bfd_elf_set_group_contents): Replace use of abort with an assert. (assign_section_numbers): Use resolve_section_groups flag instead of relocatable link type. (_bfd_elf_init_private_section_data): Use resolve_section_groups flag instead of checking the final_link flag for part of the checks in here. Fix white space as a result. * elflink.c (elf_link_input_bfd): Use resolve_section_groups flag instead of relocatable link type. (bfd_elf_final_link): Likewise. include/ChangeLog: * bfdlink.h (struct bfd_link_info): Add new resolve_section_groups flag. ld/ChangeLog: * ld.h (struct args_type): Add force_group_allocation field. * ldgram.y: Add support for FORCE_GROUP_ALLOCATION. * ldlex.h: Likewise. * ldlex.l: Likewise. * lexsup.c: Likewise. * ldlang.c (unique_section_p): Check resolve_section_groups flag not the relaxable link flag. (lang_add_section): Discard section groups when we're resolving groups. Clear the SEC_LINK_ONCE flag if we're resolving section groups. * ldmain.c (main): Initialise resolve_section_groups flag in link_info based on command line flags. * testsuite/ld-elf/group11.d: New file. * testsuite/ld-elf/group12.d: New file. * testsuite/ld-elf/group12.ld: New file. * NEWS: Mention new features. * ld.texinfo (Options): Document --force-group-allocation. (Miscellaneous Commands): Document FORCE_GROUP_ALLOCATION.
This commit is contained in:
Andrew Burgess
parent
458ad2b83e
commit
7bdf4127c3
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@ -1,3 +1,17 @@
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2017-06-06 Andrew Burgess <andrew.burgess@embecosm.com>
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* elf.c (_bfd_elf_make_section_from_shdr): Don't initially mark
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SEC_GROUP sections as SEC_EXCLUDE.
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(bfd_elf_set_group_contents): Replace use of abort with an assert.
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(assign_section_numbers): Use resolve_section_groups flag instead
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of relocatable link type.
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(_bfd_elf_init_private_section_data): Use resolve_section_groups
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flag instead of checking the final_link flag for part of the
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checks in here. Fix white space as a result.
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* elflink.c (elf_link_input_bfd): Use resolve_section_groups flag
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instead of relocatable link type.
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(bfd_elf_final_link): Likewise.
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2017-06-06 Jose E. Marchesi <jose.marchesi@oracle.com>
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* elfxx-mips.c (_bfd_mips_elf_relocate_section): Remove unused
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35
bfd/elf.c
35
bfd/elf.c
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@ -983,7 +983,7 @@ _bfd_elf_make_section_from_shdr (bfd *abfd,
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if (hdr->sh_type != SHT_NOBITS)
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flags |= SEC_HAS_CONTENTS;
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if (hdr->sh_type == SHT_GROUP)
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flags |= SEC_GROUP | SEC_EXCLUDE;
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flags |= SEC_GROUP;
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if ((hdr->sh_flags & SHF_ALLOC) != 0)
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{
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flags |= SEC_ALLOC;
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@ -3533,8 +3533,8 @@ bfd_elf_set_group_contents (bfd *abfd, asection *sec, void *failedptrarg)
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break;
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}
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if ((loc -= 4) != sec->contents)
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abort ();
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loc -= 4;
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BFD_ASSERT (loc == sec->contents);
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H_PUT_32 (abfd, sec->flags & SEC_LINK_ONCE ? GRP_COMDAT : 0, loc);
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}
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@ -3609,7 +3609,7 @@ assign_section_numbers (bfd *abfd, struct bfd_link_info *link_info)
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_bfd_elf_strtab_clear_all_refs (elf_shstrtab (abfd));
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/* SHT_GROUP sections are in relocatable files only. */
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if (link_info == NULL || bfd_link_relocatable (link_info))
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if (link_info == NULL || !link_info->resolve_section_groups)
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{
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size_t reloc_count = 0;
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@ -7445,23 +7445,22 @@ _bfd_elf_init_private_section_data (bfd *ibfd,
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SHT_GROUP section will have its elf_next_in_group pointing back
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to the input group members. Ignore linker created group section.
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See elfNN_ia64_object_p in elfxx-ia64.c. */
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if (!final_link)
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if ((link_info == NULL
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|| !link_info->resolve_section_groups)
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&& (elf_sec_group (isec) == NULL
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|| (elf_sec_group (isec)->flags & SEC_LINKER_CREATED) == 0))
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{
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if (elf_sec_group (isec) == NULL
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|| (elf_sec_group (isec)->flags & SEC_LINKER_CREATED) == 0)
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{
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if (elf_section_flags (isec) & SHF_GROUP)
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elf_section_flags (osec) |= SHF_GROUP;
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elf_next_in_group (osec) = elf_next_in_group (isec);
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elf_section_data (osec)->group = elf_section_data (isec)->group;
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}
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/* If not decompress, preserve SHF_COMPRESSED. */
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if ((ibfd->flags & BFD_DECOMPRESS) == 0)
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elf_section_flags (osec) |= (elf_section_flags (isec)
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& SHF_COMPRESSED);
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if (elf_section_flags (isec) & SHF_GROUP)
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elf_section_flags (osec) |= SHF_GROUP;
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elf_next_in_group (osec) = elf_next_in_group (isec);
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elf_section_data (osec)->group = elf_section_data (isec)->group;
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}
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/* If not decompress, preserve SHF_COMPRESSED. */
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if (!final_link && (ibfd->flags & BFD_DECOMPRESS) == 0)
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elf_section_flags (osec) |= (elf_section_flags (isec)
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& SHF_COMPRESSED);
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ihdr = &elf_section_data (isec)->this_hdr;
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/* We need to handle elf_linked_to_section for SHF_LINK_ORDER. We
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@ -10277,7 +10277,7 @@ elf_link_input_bfd (struct elf_final_link_info *flinfo, bfd *input_bfd)
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continue;
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}
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if (bfd_link_relocatable (flinfo->info)
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if (!flinfo->info->resolve_section_groups
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&& (o->flags & (SEC_LINKER_CREATED | SEC_GROUP)) == SEC_GROUP)
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{
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/* Deal with the group signature symbol. */
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@ -10285,6 +10285,7 @@ elf_link_input_bfd (struct elf_final_link_info *flinfo, bfd *input_bfd)
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unsigned long symndx = sec_data->this_hdr.sh_info;
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asection *osec = o->output_section;
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BFD_ASSERT (bfd_link_relocatable (flinfo->info));
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if (symndx >= locsymcount
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|| (elf_bad_symtab (input_bfd)
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&& flinfo->sections[symndx] == NULL))
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@ -12463,10 +12464,11 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
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}
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}
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if (bfd_link_relocatable (info))
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if (!info->resolve_section_groups)
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{
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bfd_boolean failed = FALSE;
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BFD_ASSERT (bfd_link_relocatable (info));
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bfd_map_over_sections (abfd, bfd_elf_set_group_contents, &failed);
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if (failed)
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goto error_return;
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@ -1,3 +1,8 @@
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2017-06-06 Andrew Burgess <andrew.burgess@embecosm.com>
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* bfdlink.h (struct bfd_link_info): Add new resolve_section_groups
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flag.
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2017-06-01 Alan Modra <amodra@gmail.com>
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* elf/ppc64.h (PPC64_OPT_LOCALENTRY): Define.
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@ -348,6 +348,9 @@ struct bfd_link_info
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/* TRUE if all data symbols should be dynamic. */
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unsigned int dynamic_data: 1;
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/* TRUE if section groups should be resolved. */
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unsigned int resolve_section_groups: 1;
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/* Which symbols to strip. */
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ENUM_BITFIELD (bfd_link_strip) strip : 2;
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21
ld/ChangeLog
21
ld/ChangeLog
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@ -1,3 +1,24 @@
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2017-06-06 Andrew Burgess <andrew.burgess@embecosm.com>
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* ld.h (struct args_type): Add force_group_allocation field.
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* ldgram.y: Add support for FORCE_GROUP_ALLOCATION.
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* ldlex.h: Likewise.
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* ldlex.l: Likewise.
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* lexsup.c: Likewise.
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* ldlang.c (unique_section_p): Check resolve_section_groups flag
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not the relaxable link flag.
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(lang_add_section): Discard section groups when we're resolving
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groups. Clear the SEC_LINK_ONCE flag if we're resolving section
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groups.
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* ldmain.c (main): Initialise resolve_section_groups flag in
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link_info based on command line flags.
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* testsuite/ld-elf/group11.d: New file.
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* testsuite/ld-elf/group12.d: New file.
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* testsuite/ld-elf/group12.ld: New file.
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* NEWS: Mention new features.
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* ld.texinfo (Options): Document --force-group-allocation.
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(Miscellaneous Commands): Document FORCE_GROUP_ALLOCATION.
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2017-06-05 H.J. Lu <hongjiu.lu@intel.com>
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PR ld/21529
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5
ld/NEWS
5
ld/NEWS
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@ -15,6 +15,11 @@
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* Orphan sections placed after an empty section that has an AT(LMA) will now
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take an load memory address starting from LMA.
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* Section groups can now be resolved (the group deleted and the group members
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placed like normal sections) at partial link time either using the new linker
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option --force-group-allocation or by placing FORCE_GROUP_ALLOCATION into the
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linker script.
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Changes in 2.28:
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* The EXCLUDE_FILE linker script construct can now be applied outside of the
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5
ld/ld.h
5
ld/ld.h
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@ -172,6 +172,11 @@ typedef struct
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/* If set, display the target memory usage (per memory region). */
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bfd_boolean print_memory_usage;
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/* Shold we force section groups to be resolved? Controlled with
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--force-group-allocation on the command line or FORCE_GROUP_ALLOCATION
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in the linker script. */
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bfd_boolean force_group_allocation;
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/* Big or little endian as set on command line. */
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enum endian_enum endian;
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@ -1484,6 +1484,18 @@ and also prevents any possible confusion over resolving to the wrong
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duplicate when there are many dynamic modules with specialized search
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paths for runtime symbol resolution.
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@cindex group allocation in linker script
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@cindex section groups
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@cindex COMDAT
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@kindex --force-group-allocation
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@item --force-group-allocation
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This option causes the linker to place section group members like
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normal input sections, and to delete the section groups. This is the
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default behaviour for a final link but this option can be used to
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change the behaviour of a relocatable link (@samp{-r}). The script
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command @code{FORCE_GROUP_ALLOCATION} has the same
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effect. @xref{Miscellaneous Commands}.
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@cindex symbols, from command line
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@kindex --defsym=@var{symbol}=@var{exp}
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@item --defsym=@var{symbol}=@var{expression}
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@ -3726,6 +3738,17 @@ This command has the same effect as the @samp{--no-define-common}
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command-line option: to make @code{ld} omit the assignment of addresses
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to common symbols even for a non-relocatable output file.
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@item FORCE_GROUP_ALLOCATION
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@kindex FORCE_GROUP_ALLOCATION
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@cindex group allocation in linker script
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@cindex section groups
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@cindex COMDAT
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This command has the same effect as the
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@samp{--force-group-allocation} command-line option: to make
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@command{ld} place section group members like normal input sections,
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and to delete the section groups even if a relocatable output file is
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specified (@samp{-r}).
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@item INSERT [ AFTER | BEFORE ] @var{output_section}
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@kindex INSERT
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@cindex insert user script into default script
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@ -131,7 +131,7 @@ static int error_index;
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%token SORT_BY_INIT_PRIORITY
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%token '{' '}'
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%token SIZEOF_HEADERS OUTPUT_FORMAT FORCE_COMMON_ALLOCATION OUTPUT_ARCH
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%token INHIBIT_COMMON_ALLOCATION
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%token INHIBIT_COMMON_ALLOCATION FORCE_GROUP_ALLOCATION
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%token SEGMENT_START
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%token INCLUDE
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%token MEMORY
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@ -336,6 +336,8 @@ ifile_p1:
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{ ldfile_set_output_arch ($3, bfd_arch_unknown); }
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| FORCE_COMMON_ALLOCATION
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{ command_line.force_common_definition = TRUE ; }
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| FORCE_GROUP_ALLOCATION
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{ command_line.force_group_allocation = TRUE ; }
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| INHIBIT_COMMON_ALLOCATION
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{ command_line.inhibit_common_definition = TRUE ; }
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| INPUT '(' input_list ')'
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18
ld/ldlang.c
18
ld/ldlang.c
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@ -207,7 +207,7 @@ unique_section_p (const asection *sec,
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struct unique_sections *unam;
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const char *secnam;
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if (bfd_link_relocatable (&link_info)
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if (!link_info.resolve_section_groups
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&& sec->owner != NULL
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&& bfd_is_group_section (sec->owner, sec))
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return !(os != NULL
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@ -2349,6 +2349,12 @@ lang_add_section (lang_statement_list_type *ptr,
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if (strcmp (output->name, DISCARD_SECTION_NAME) == 0)
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discard = TRUE;
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/* Discard the group descriptor sections when we're finally placing the
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sections from within the group. */
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if ((section->flags & SEC_GROUP) == SEC_GROUP
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&& link_info.resolve_section_groups)
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discard = TRUE;
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/* Discard debugging sections if we are stripping debugging
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information. */
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if ((link_info.strip == strip_debugger || link_info.strip == strip_all)
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@ -2389,8 +2395,14 @@ lang_add_section (lang_statement_list_type *ptr,
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already been processed. One reason to do this is that on pe
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format targets, .text$foo sections go into .text and it's odd
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to see .text with SEC_LINK_ONCE set. */
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if (!bfd_link_relocatable (&link_info))
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if ((flags & (SEC_LINK_ONCE | SEC_GROUP)) == (SEC_LINK_ONCE | SEC_GROUP))
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{
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if (link_info.resolve_section_groups)
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flags &= ~(SEC_LINK_ONCE | SEC_LINK_DUPLICATES | SEC_RELOC);
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else
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flags &= ~(SEC_LINK_DUPLICATES | SEC_RELOC);
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}
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else if (!bfd_link_relocatable (&link_info))
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flags &= ~(SEC_LINK_ONCE | SEC_LINK_DUPLICATES | SEC_RELOC);
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switch (output->sectype)
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@ -146,6 +146,7 @@ enum option_values
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OPTION_PRINT_MEMORY_USAGE,
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OPTION_REQUIRE_DEFINED_SYMBOL,
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OPTION_ORPHAN_HANDLING,
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OPTION_FORCE_GROUP_ALLOCATION,
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};
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/* The initial parser states. */
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@ -274,6 +274,7 @@ V_IDENTIFIER [*?.$_a-zA-Z\[\]\-\!\^\\]([*?.$_a-zA-Z0-9\[\]\-\!\^\\]|::)*
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<BOTH,SCRIPT>"CREATE_OBJECT_SYMBOLS" { RTOKEN(CREATE_OBJECT_SYMBOLS);}
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<BOTH,SCRIPT>"CONSTRUCTORS" { RTOKEN( CONSTRUCTORS);}
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<BOTH,SCRIPT>"FORCE_COMMON_ALLOCATION" { RTOKEN(FORCE_COMMON_ALLOCATION);}
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<BOTH,SCRIPT>"FORCE_GROUP_ALLOCATION" { RTOKEN(FORCE_GROUP_ALLOCATION);}
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<BOTH,SCRIPT>"INHIBIT_COMMON_ALLOCATION" { RTOKEN(INHIBIT_COMMON_ALLOCATION);}
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<BOTH,SCRIPT>"SECTIONS" { RTOKEN(SECTIONS);}
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<BOTH,SCRIPT>"INSERT" { RTOKEN(INSERT_K);}
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@ -386,6 +386,12 @@ main (int argc, char **argv)
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info_msg ("\n==================================================\n");
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}
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if (command_line.force_group_allocation
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|| !bfd_link_relocatable (&link_info))
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link_info.resolve_section_groups = TRUE;
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else
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link_info.resolve_section_groups = FALSE;
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if (command_line.print_output_format)
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info_msg ("%s\n", lang_get_output_target ());
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@ -112,6 +112,9 @@ static const struct ld_option ld_options[] =
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'd', NULL, N_("Force common symbols to be defined"), ONE_DASH },
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{ {"dp", no_argument, NULL, 'd'},
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'\0', NULL, NULL, ONE_DASH },
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{ {"force-group-allocation", no_argument, NULL,
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OPTION_FORCE_GROUP_ALLOCATION},
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'\0', NULL, N_("Force group members out of groups"), TWO_DASHES },
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{ {"entry", required_argument, NULL, 'e'},
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'e', N_("ADDRESS"), N_("Set start address"), TWO_DASHES },
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{ {"export-dynamic", no_argument, NULL, OPTION_EXPORT_DYNAMIC},
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@ -767,6 +770,9 @@ parse_args (unsigned argc, char **argv)
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case 'd':
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command_line.force_common_definition = TRUE;
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break;
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case OPTION_FORCE_GROUP_ALLOCATION:
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command_line.force_group_allocation = TRUE;
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break;
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case OPTION_DEFSYM:
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lex_string = optarg;
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lex_redirect (optarg, "--defsym", ++defsym_count);
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@ -0,0 +1,6 @@
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#source: group1a.s
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#source: group1b.s
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#ld: -r --force-group-allocation
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#readelf: -g
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There are no section groups in this file.
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||||
|
|
@ -0,0 +1,6 @@
|
|||
#source: group1a.s
|
||||
#source: group1b.s
|
||||
#ld: -r -T group12.ld
|
||||
#readelf: -g
|
||||
|
||||
There are no section groups in this file.
|
||||
|
|
@ -0,0 +1,14 @@
|
|||
FORCE_GROUP_ALLOCATION
|
||||
|
||||
PHDRS
|
||||
{
|
||||
header PT_PHDR PHDRS ;
|
||||
image PT_LOAD PHDRS;
|
||||
}
|
||||
|
||||
SECTIONS
|
||||
{
|
||||
. = 0x1000;
|
||||
.text : { *(.text) *(.rodata.brlt) } :image :header
|
||||
/DISCARD/ : { *(.dropme) *(.reginfo) *(.MIPS.abiflags) }
|
||||
}
|
||||
Loading…
Reference in New Issue