From: Fangrui Song <i@maskray.me>
Date: Fri, 26 Feb 2021 19:10:02 +0000 (-0800)
Subject: [SanitizerCoverage] Clarify llvm.used/llvm.compiler.used and partially fix unmatched... 
X-Git-Tag: llvmorg-14-init~13926
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=b55f29c194d31cb51096d80b5e2710fc3385a7ef;p=platform%2Fupstream%2Fllvm.git

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

`__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
---

diff --git a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
index 69512fd..843a27f 100644
--- a/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
+++ b/llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp
@@ -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;
 }
diff --git a/llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll b/llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll
index a3b3aa8..6dbbbff 100644
--- a/llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll
+++ b/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