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[BOLT] Fix writing out unmarked .eh_frame section

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When BOLT updates .eh_frame section, it concatenates newly-generated
contents (from CFI directives) with the original .eh_frame that has
relocations applied to it. However, if no new content is generated,
the original .eh_frame has to be left intact. In that case, BOLT was
still writing out the relocatable copy of the original .eh_frame section
to the new segment, even though this copy was never used and was not
even marked in the section header table.

Detect the scenario above and skip allocating extra space for .eh_frame.

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D135223
This commit is contained in:
Maksim Panchenko 2022-10-03 18:50:18 -07:00
parent c683e281cd
commit 0b213c9090
2 changed files with 37 additions and 0 deletions
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10
bolt/lib/Rewrite/RewriteInstance.cpp
View File

@ -3798,6 +3798,16 @@ void RewriteInstance::mapDataSections(RuntimeDyld &RTDyld) {
if (RuntimeLibrary *RtLibrary = BC->getRuntimeLibrary())
RtLibrary->addRuntimeLibSections(Sections);
if (!EHFrameSection || !EHFrameSection->isFinalized()) {
ErrorOr<BinarySection &> OldEHFrameSection =
BC->getUniqueSectionByName(Twine(getOrgSecPrefix(), ".eh_frame").str());
if (OldEHFrameSection) {
RTDyld.reassignSectionAddress(OldEHFrameSection->getSectionID(),
NextAvailableAddress);
BC->deregisterSection(*OldEHFrameSection);
}
}
for (std::string &SectionName : Sections) {
ErrorOr<BinarySection &> Section = BC->getUniqueSectionByName(SectionName);
if (!Section || !Section->isAllocatable() || !Section->isFinalized())

27
bolt/test/X86/dummy-eh-frame-bug.s Normal file
View File

@ -0,0 +1,27 @@
# REQUIRES: system-linux
# RUN: llvm-mc -filetype=obj -triple x86_64-unknown-linux %s -o %t.o
# RUN: ld.lld %t.o -o %t.exe -q
# RUN: llvm-bolt %t.exe -o %t.bolt.exe --funcs=nocfi_function
# RUN: llvm-readelf --section-headers %t.bolt.exe | FileCheck %s
## Check that llvm-bolt does not allocate unmarked space for original .eh_frame
## after .text when no update is needed to .eh_frame.
# CHECK: {{ .text}} PROGBITS [[#%x,ADDR:]] [[#%x,OFFSET:]] [[#%x,SIZE:]]
# CHECK-NEXT: 0000000000000000 [[#%x, OFFSET + SIZE]]
.text
.globl nocfi_function
.type nocfi_function,@function
nocfi_function:
ret
.size nocfi_function, .-nocfi_function
.globl _start
.type _start,@function
_start:
.cfi_startproc
call nocfi_function
.size _start, .-_start
.cfi_endproc