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[llvm-readobj] Construct relocation-aware DWARFDataExtractor to decode .eh_frame addresses correctly 

In an object file, a "PC Begin" field in a FDE is usually relocated by a
PC-relative relocation. Use a relocation-aware DWARFDataExtractor overload (with
DWARFContext and a reference to its internal .eh_frame representation) to decode
addresses correctly. In an object file, most sections have addresses of zero. So
the displayed addresses are almost always offsets relative to the start of the
associated text section.

DWARFContext::create handles .eh_frame and .rela.eh_frame by itself, so if there
are more than one .eh_frame (technically possible, but almost always erronerous
in practice), this will only handle the first one.  Supporting multiple
.eh_frame is beyond the scope of this patch.

Reviewed By: grimar, jhenderson

Differential Revision: https://reviews.llvm.org/D84106
This commit is contained in:
Fangrui Song 2020-07-21 08:24:42 -07:00
parent 741e55aeed
commit 8c6d48baf6
3 changed files with 9 additions and 7 deletions
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5
llvm/test/tools/llvm-readobj/ELF/AArch64/dwarf-cfi.s
View File

@ -10,10 +10,9 @@
# CHECK: Program:
# CHECK-NEXT: DW_CFA_def_cfa: reg31 +0
## FIXME Use getEHFrameSection() so that the address is decoded correctly.
# CHECK: [0x14] FDE length=16 cie=[0x0]
# CHECK-NEXT: initial_location: 0x1c
# CHECK-NEXT: address_range: 0x4 (end : 0x20)
# CHECK-NEXT: initial_location: 0x0
# CHECK-NEXT: address_range: 0x4 (end : 0x4)
# CHECK: Program:
# CHECK-NEXT: DW_CFA_nop:

5
llvm/test/tools/llvm-readobj/ELF/ARM/dwarf-cfi.s
View File

@ -10,10 +10,9 @@
# CHECK: Program:
# CHECK-NEXT: DW_CFA_def_cfa: reg13 +0
## FIXME Use getEHFrameSection() so that the address is decoded correctly.
# CHECK: [0x14] FDE length=16 cie=[0x0]
# CHECK-NEXT: initial_location: 0x1c
# CHECK-NEXT: address_range: 0x4 (end : 0x20)
# CHECK-NEXT: initial_location: 0x0
# CHECK-NEXT: address_range: 0x4 (end : 0x4)
# CHECK: Program:
# CHECK-NEXT: DW_CFA_nop:

6
llvm/tools/llvm-readobj/DwarfCFIEHPrinter.h
View File

@ -13,6 +13,7 @@
#include "llvm-readobj.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugFrame.h"
#include "llvm/Object/ELF.h"
@ -185,7 +186,10 @@ void PrinterContext<ELFT>::printEHFrame(const Elf_Shdr *EHFrameShdr) const {
if (!DataOrErr)
reportError(DataOrErr.takeError(), ObjF->getFileName());
DWARFDataExtractor DE(*DataOrErr,
// Construct DWARFDataExtractor to handle relocations ("PC Begin" fields).
std::unique_ptr<DWARFContext> DICtx = DWARFContext::create(*ObjF, nullptr);
DWARFDataExtractor DE(DICtx->getDWARFObj(),
DICtx->getDWARFObj().getEHFrameSection(),
ELFT::TargetEndianness == support::endianness::little,
ELFT::Is64Bits ? 8 : 4);
DWARFDebugFrame EHFrame(Triple::ArchType(ObjF->getArch()), /*IsEH=*/true,