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[SanitizerCoverage] Clarify llvm.used/llvm.compiler.used and partially fix unmatched metadata sections on Windows

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`__sancov_pcs` parallels the other metadata section(s). While some optimizers
(e.g. GlobalDCE) respect linker semantics for comdat and retain or discard the
sections as a unit, some (e.g.  GlobalOpt/ConstantMerge) do not. So we have to
conservatively retain all unconditionally in the compiler.

When a comdat is used, the COFF/ELF linkers' GC semantics ensure the
associated parallel array elements are retained or discarded together,
so `llvm.compiler.used` is sufficient.

Otherwise (MachO (see rL311955/rL311959), COFF special case where comdat is not
used), we have to use `llvm.used` to conservatively make all sections retain by
the linker. This will fix the Windows problem once internal linkage
GlobalObject's in `llvm.used` are retained via `/INCLUDE:`.

Reviewed By: morehouse, vitalybuka

Differential Revision: https://reviews.llvm.org/D97432
This commit is contained in:
Fangrui Song 2021-02-26 11:10:02 -08:00
parent 86325e758d
commit 95d9b0ea49
2 changed files with 29 additions and 11 deletions
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21
lib/Transforms/Instrumentation/SanitizerCoverage.cpp
View File

@ -499,10 +499,7 @@ bool ModuleSanitizerCoverage::instrumentModule(
IRBuilder<> IRBCtor(Ctor->getEntryBlock().getTerminator());
IRBCtor.CreateCall(InitFunction, {SecStartEnd.first, SecStartEnd.second});
}
// We don't reference these arrays directly in any of our runtime functions,
// so we need to prevent them from being dead stripped.
if (TargetTriple.isOSBinFormatMachO())
appendToUsed(M, GlobalsToAppendToUsed);
appendToUsed(M, GlobalsToAppendToUsed);
appendToCompilerUsed(M, GlobalsToAppendToCompilerUsed);
return true;
}
@ -682,8 +679,20 @@ GlobalVariable *ModuleSanitizerCoverage::CreateFunctionLocalArrayInSection(
Array->setComdat(Comdat);
Array->setSection(getSectionName(Section));
Array->setAlignment(Align(DL->getTypeStoreSize(Ty).getFixedSize()));
GlobalsToAppendToUsed.push_back(Array);
GlobalsToAppendToCompilerUsed.push_back(Array);
// sancov_pcs parallels the other metadata section(s). Optimizers (e.g.
// GlobalOpt/ConstantMerge) may not discard sancov_pcs and the other
// section(s) as a unit, so we conservatively retain all unconditionally in
// the compiler.
//
// With comdat (COFF/ELF), the linker can guarantee the associated sections
// will be retained or discarded as a unit, so llvm.compiler.used is
// sufficient. Otherwise, conservatively make all of them retained by the
// linker.
if (Array->hasComdat())
GlobalsToAppendToCompilerUsed.push_back(Array);
else
GlobalsToAppendToUsed.push_back(Array);
return Array;
}

19
test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll
View File

@ -1,20 +1,29 @@
; RUN: opt < %s -sancov -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=x86_64 -S -enable-new-pm=0 | FileCheck %s --check-prefixes=CHECK,ELF
; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=x86_64 -S | FileCheck %s --check-prefixes=CHECK,ELF
; RUN: opt < %s -sancov -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=x86_64 -S -enable-new-pm=0 | FileCheck %s --check-prefixes=CHECK,COMDAT,ELF
; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=x86_64 -S | FileCheck %s --check-prefixes=CHECK,COMDAT,ELF
; RUN: opt < %s -sancov -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=aarch64-apple-darwin -S -enable-new-pm=0 | FileCheck %s --check-prefixes=CHECK,MACHO
; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=aarch64-apple-darwin -S | FileCheck %s --check-prefixes=CHECK,MACHO
; ELF: $foo = comdat noduplicates
; ELF: $CallViaVptr = comdat noduplicates
; RUN: opt < %s -passes='module(sancov-module)' -sanitizer-coverage-level=4 -sanitizer-coverage-trace-pc-guard -mtriple=x86_64-windows -S | FileCheck %s --check-prefixes=CHECK,COMDAT,WIN
; COMDAT: $foo = comdat noduplicates
; COMDAT: $CallViaVptr = comdat noduplicates
; ELF: @__sancov_gen_ = private global [3 x i32] zeroinitializer, section "__sancov_guards", comdat($foo), align 4{{$}}
; ELF-NEXT: @__sancov_gen_.1 = private global [1 x i32] zeroinitializer, section "__sancov_guards", comdat($CallViaVptr), align 4{{$}}
; MACHO: @__sancov_gen_ = private global [3 x i32] zeroinitializer, section "__DATA,__sancov_guards", align 4{{$}}
; MACHO-NEXT: @__sancov_gen_.1 = private global [1 x i32] zeroinitializer, section "__DATA,__sancov_guards", align 4{{$}}
; WIN: @__sancov_gen_ = private global [3 x i32] zeroinitializer, section ".SCOV$GM", comdat($foo), align 4{{$}}
; WIN-NEXT: @__sancov_gen_.1 = private global [1 x i32] zeroinitializer, section ".SCOV$GM", comdat($CallViaVptr), align 4{{$}}
; ELF-NOT: @llvm.used =
; ELF: @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"
; MACHO: @llvm.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"
; CHECK: @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"
; MACHO-NOT: @llvm.compiler.used =
; WIN: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @sancov.module_ctor_trace_pc_guard to i8*)], section "llvm.metadata"
; WIN-NEXT: @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"
; CHECK-LABEL: define void @foo
; CHECK: call void @__sanitizer_cov_trace_pc