[PATCH] D97432: [SanitizerCoverage] Clarify llvm.used/llvm.compiler.used and fix unmatched metadata sections on Windows

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 326458.
MaskRay retitled this revision from "[SanitizerCoverage] Don't use llvm.used if comdat" to "[SanitizerCoverage] Clarify llvm.used/llvm.compiler.used and fix unmatched metadata sections on Windows".
MaskRay edited the summary of this revision.
MaskRay added a comment.

Fix a bug on Windows


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D97432/new/

https://reviews.llvm.org/D97432

Files:
  llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
  llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll


Index: llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll
===================================================================
--- llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll
+++ llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll
@@ -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
Index: llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -499,10 +499,7 @@
     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 @@
       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;
 }


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