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llvm-objcopy: Set sh_link to 0 on unrecognized symtab-linked sections.

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Per discussion on the generic-abi mailing list:
https://groups.google.com/forum/#!topic/generic-abi/MPr8TVtnVn4

An object file manipulation tool must either write out a symbol
table with the same number of entries as the original symbol table
and in the same order, or if this is impossible, refuse to operate
on the object file if it has unrecognized sections that are linked
to the symtab section. However, existing tools (namely GNU strip,
GNU objcopy and ld.{bfd,gold,lld} -r) do not comply with this at
present: they change symbol table indexes and set sh_link to 0 on
the unrecognized symtab-linked sections.

We intend to use the latter as a (temporary) signal that a tool has
operated on a proposed new symtab-linked section and invalidated the
symbol table indexes. However, llvm-objcopy currently keeps sh_link
pointing to the new symtab section. This patch changes llvm-objcopy
to set sh_link to 0 to match the behaviour of the other tools.

Differential Revision: https://reviews.llvm.org/D47404

llvm-svn: 333581
This commit is contained in:
Peter Collingbourne 2018-05-30 19:30:39 +00:00
parent 693cbc43af
commit 33177b3e92
2 changed files with 32 additions and 3 deletions
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27
test/tools/llvm-objcopy/symtab-link.test Normal file
View File

@ -0,0 +1,27 @@
# RUN: yaml2obj %s > %t
# RUN: llvm-objcopy %t %t2
# RUN: llvm-readobj -sections %t2 | FileCheck %s
# RUN: cp %t %t3
# RUN: llvm-strip --strip-debug %t3
# RUN: llvm-readobj -sections %t3 | FileCheck %s
!ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_X86_64
Sections:
- Name: .foo
Link: .symtab
Type: SHT_PROGBITS
Flags: [ ]
# CHECK: Name: .foo
# CHECK-NEXT: Type:
# CHECK-NEXT: Flags [ (0x0)
# CHECK-NEXT: ]
# CHECK-NEXT: Address:
# CHECK-NEXT: Offset:
# CHECK-NEXT: Size:
# CHECK-NEXT: Link: 0

8
tools/llvm-objcopy/Object.cpp
View File

@ -401,15 +401,17 @@ void GroupSection::markSymbols() {
}
void Section::initialize(SectionTableRef SecTable) {
if (Link != ELF::SHN_UNDEF)
if (Link != ELF::SHN_UNDEF) {
LinkSection =
SecTable.getSection(Link, "Link field value " + Twine(Link) +
" in section " + Name + " is invalid");
if (LinkSection->Type == ELF::SHT_SYMTAB)
LinkSection = nullptr;
}
}
void Section::finalize() {
if (LinkSection)
this->Link = LinkSection->Index;
this->Link = LinkSection ? LinkSection->Index : 0;
}
void GnuDebugLinkSection::init(StringRef File, StringRef Data) {