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[SanitizerCoverage] Add associated metadata to PC guards. 

Summary:
Without this metadata LLD strips unused PC table entries
but won't strip unused guards.  This metadata also seems
to influence the linker to change the ordering in the PC
guard section to match that of the PC table section.

The libFuzzer runtime library depends on the ordering
of the PC table and PC guard sections being the same.  This
is not generally guaranteed, so we may need to redesign
PC tables/guards/counters in the future.

Reviewers: eugenis

Reviewed By: eugenis

Subscribers: kcc, hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D50483

llvm-svn: 339733
This commit is contained in:
Matt Morehouse 2018-08-14 22:04:34 +00:00
parent cd4056c881
commit 0f22fac274
2 changed files with 9 additions and 1 deletions
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7
compiler-rt/test/fuzzer/gc-sections.test
View File

@ -8,8 +8,13 @@ With gc-sections. Currently, we can't remove unused code except with LLD.
RUN: %cpp_compiler %S/GcSectionsTest.cpp -o %t -fuse-ld=lld -ffunction-sections -Wl,-gc-sections
RUN: nm %t | not grep UnusedFunctionShouldBeRemovedByLinker
RUN: %run %t -runs=0 2>&1 | FileCheck %s
CHECK-NOT: ERROR: The size of coverage PC tables does not match
With gc sections, with trace-pc. Unused code is removed.
RUN: %cpp_compiler %S/GcSectionsTest.cpp -o %t -fsanitize-coverage=0 -fsanitize-coverage=trace-pc -ffunction-sections -Wl,-gc-sections
RUN: nm %t | not grep UnusedFunctionShouldBeRemovedByLinker
RUN: %cpp_compiler %S/GcSectionsTest.cpp -o %t -fsanitize-coverage=0 -fsanitize-coverage=trace-pc-guard,pc-table -fuse-ld=lld -ffunction-sections -Wl,-gc-sections
RUN: nm %t | not grep UnusedFunctionShouldBeRemovedByLinker
RUN: %run %t -runs=0 2>&1 | FileCheck %s
CHECK-NOT: ERROR: The size of coverage PC tables does not match

3
llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
View File

@ -591,6 +591,9 @@ void SanitizerCoverageModule::CreateFunctionLocalArrays(
FunctionGuardArray = CreateFunctionLocalArrayInSection(
AllBlocks.size(), F, Int32Ty, SanCovGuardsSectionName);
GlobalsToAppendToUsed.push_back(FunctionGuardArray);
GlobalsToAppendToCompilerUsed.push_back(FunctionGuardArray);
MDNode *MD = MDNode::get(F.getContext(), ValueAsMetadata::get(&F));
FunctionGuardArray->addMetadata(LLVMContext::MD_associated, *MD);
}
if (Options.Inline8bitCounters) {
Function8bitCounterArray = CreateFunctionLocalArrayInSection(