replica
/
hanchenye-llvm-project
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

[ELF] Use pcrel format for eh_frame_ptr field encoding 

The `eh_frame_ptr` field in the `.eh_frame_hdr` section contains an address
of the `.eh_frame` section. Using an absolute 32-bit format for encoding
of this field does not work for 64-bit targets. It is better to use a
relative format because it covers both 32-bit and 64-bit cases. Sure
this work if a distance between `.eh_frame_hdr` and `.eh_frame` sections
is less than 4 Gb but it is a rather correct assumption.

http://reviews.llvm.org/D8352

llvm-svn: 232414
This commit is contained in:
Simon Atanasyan 2015-03-16 21:07:46 +00:00
parent 9255a5535a
commit 4b4706b601
2 changed files with 18 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
lld/lib/ReaderWriter/ELF/SectionChunks.h
View File

@ -1450,7 +1450,8 @@ template <class ELFT> class EHFrameHeader : public Section<ELFT> {
public:
EHFrameHeader(const ELFLinkingContext &context, StringRef name,
TargetLayout<ELFT> &layout, int32_t order)
: Section<ELFT>(context, name, "EHFrameHeader"), _layout(layout) {
: Section<ELFT>(context, name, "EHFrameHeader"), _ehFrameOffset(0),
_layout(layout) {
this->setOrder(order);
this->_entSize = 0;
this->_type = SHT_PROGBITS;
@ -1467,24 +1468,27 @@ public:
void finalize() override {
OutputSection<ELFT> *s = _layout.findOutputSection(".eh_frame");
_ehFrameAddr = s ? s->virtualAddr() : 0;
OutputSection<ELFT> *h = _layout.findOutputSection(".eh_frame_hdr");
if (s && h)
_ehFrameOffset = s->virtualAddr() - (h->virtualAddr() + 4);
}
virtual void write(ELFWriter *writer, TargetLayout<ELFT> &layout,
llvm::FileOutputBuffer &buffer) override {
void write(ELFWriter *writer, TargetLayout<ELFT> &layout,
llvm::FileOutputBuffer &buffer) override {
uint8_t *chunkBuffer = buffer.getBufferStart();
uint8_t *dest = chunkBuffer + this->fileOffset();
int pos = 0;
dest[pos++] = 1; // version
dest[pos++] = llvm::dwarf::DW_EH_PE_udata4; // eh_frame_ptr_enc
dest[pos++] = llvm::dwarf::DW_EH_PE_pcrel |
llvm::dwarf::DW_EH_PE_sdata4; // eh_frame_ptr_enc
dest[pos++] = llvm::dwarf::DW_EH_PE_omit; // fde_count_enc
dest[pos++] = llvm::dwarf::DW_EH_PE_omit; // table_enc
*reinterpret_cast<typename llvm::object::ELFFile<ELFT>::Elf_Word *>(
dest + pos) = (uint32_t)_ehFrameAddr;
*reinterpret_cast<typename llvm::object::ELFFile<ELFT>::Elf_Sword *>(
dest + pos) = _ehFrameOffset;
}
private:
uint64_t _ehFrameAddr;
int32_t _ehFrameOffset;
TargetLayout<ELFT> &_layout;
};
} // end namespace elf

8
lld/test/elf/eh_frame_hdr.test
View File

@ -1,7 +1,7 @@
#RUN: yaml2obj -format=elf %s > %t
#RUN: lld -flavor gnu -target x86_64-linux %t --noinhibit-exec \
#RUN: -o %t1
#RUN: llvm-readobj -s %t1 | FileCheck %s
#RUN: llvm-objdump -s %t1 | FileCheck %s
!ELF
FileHeader:
@ -23,4 +23,8 @@ Symbols:
Type: STT_SECTION
Section: .eh_frame
#CHECK: .eh_frame_hdr
# CHECK: Contents of section .eh_frame:
# CHECK-NEXT: 4001e0 00
# CHECK-NEXT: Contents of section .eh_frame_hdr:
# CHECK-NEXT: 4001e8 011bffff f4ffffff
# ^ 0x4001e0 - 0x4001e8 - 4 = 0xfffffff4