[asan] Remove debug locations from alloca prologue instrumentation

[johannes]

Summary

This fixes https://llvm.org/PR26673

Wrong debugging information with -fsanitize=address

where asan instrumentation causes the prologue end to be computed
incorrectly: findPrologueEndLoc, looks for the first instruction
with a debug location to determine the prologue end. Since the asan
instrumentation instructions had debug locations, that prologue end was
at some instrumentation instructions, where the stack frame is still
being initialized.

I did not yet find any reason why extra debug locations are needed for
the asan instrumentations that set up the frame, they don't have a
true source location. In the debugger they are simply located at the
start of the function.

For certain other instrumentations like -fsanitize-coverage=trace-pc-guard
the same problem persists - for coverage it might be more work to fix,
since it looks like they rely on locatios of the tracee functions.

This partly reverts aaf4bb239487e0a3b20a8eaf94fc641235ba2c29

[asan] Set debug location in ASan function prologue

whose motivation was to give debug location info to the coverage callback.
Its test only ensures that the call to @__sanitizer_cov_trace_pc_guard is
given the correct source location; as the debug location is still set in
ModuleSanitizerCoverage::InjectCoverageAtBlock, the test does not break.
So -fsanitize-coverage is hopefully unaffected - I don't think it should
rely on the debug locations of asan-generated allocas.

Related revision: 3c6c14d14b40adfb581940859ede1ac7d8ceae7a

ASAN: Provide reliable debug info for local variables at -O0.

I didn't test whether this reintroduces the motivating
issue, should be OK: http://openradar.appspot.com/30433661

Below is how the X86 assembly version of the added test case changes.
It seems like a reasonable change in this case to get rid of all
those funky .loc lines and put prologue_end where user code starts.

diff
--- 2.master.s	2019-12-02 12:32:38.982959053 +0100
+++ 2.patch.s	2019-12-02 12:32:41.106246674 +0100
@@ -45,8 +45,6 @@
 	.cfi_offset %rbx, -24
 	xorl	%eax, %eax
 	movl	%eax, %ecx
- .Ltmp2:
- 	.loc	1 3 0 prologue_end      # 2.c:3:0
 	cmpl	$0, __asan_option_detect_stack_use_after_return
 	movl	%edi, 92(%rbx)          # 4-byte Spill
 	movq	%rsi, 80(%rbx)          # 8-byte Spill
@@ -57,9 +55,7 @@
 	callq	__asan_stack_malloc_0
 	movq	%rax, 72(%rbx)          # 8-byte Spill
 .LBB1_2:
- 	.loc	1 0 0 is_stmt 0         # 2.c:0:0
 	movq	72(%rbx), %rax          # 8-byte Reload
- 	.loc	1 3 0                   # 2.c:3:0
 	cmpq	$0, %rax
 	movq	%rax, %rcx
 	movq	%rax, 64(%rbx)          # 8-byte Spill
@@ -72,9 +68,7 @@
 	movq	%rax, %rsp
 	movq	%rax, 56(%rbx)          # 8-byte Spill
 .LBB1_4:
- 	.loc	1 0 0                   # 2.c:0:0
 	movq	56(%rbx), %rax          # 8-byte Reload
- 	.loc	1 3 0                   # 2.c:3:0
 	movq	%rax, 120(%rbx)
 	movq	%rax, %rcx
 	addq	$32, %rcx
@@ -99,7 +93,6 @@
 	movb	%r8b, 31(%rbx)          # 1-byte Spill
 	je	.LBB1_7
 # %bb.5:
- 	.loc	1 0 0                   # 2.c:0:0
 	movq	40(%rbx), %rax          # 8-byte Reload
 	andq	$7, %rax
 	addq	$3, %rax
@@ -118,7 +111,8 @@
 	movl	%ecx, (%rax)
 	movq	80(%rbx), %rdx          # 8-byte Reload
 	movq	%rdx, 128(%rbx)
-	.loc	1 4 3 is_stmt 1         # 2.c:4:3
+.Ltmp2:
+	.loc	1 4 3 prologue_end      # 2.c:4:3
 	movq	%rax, %rdi
 	callq	f
 	movq	48(%rbx), %rax          # 8-byte Reload

[johannes]

duplicate of https://reviews.llvm.org/D70894

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

void FunctionStackPoisoner::processStaticAllocas() {
 
   int StackMallocIdx = -1;
   DebugLoc EntryDebugLocation;
   if (auto SP = F.getSubprogram())
     EntryDebugLocation = DebugLoc::get(SP->getScopeLine(), 0, SP);
 
   Instruction *InsBefore = AllocaVec[0];
   IRBuilder<> IRB(InsBefore);
-  IRB.SetCurrentDebugLocation(EntryDebugLocation);
 
   // Make sure non-instrumented allocas stay in the entry block. Otherwise,
   // debug info is broken, because only entry-block allocas are treated as
   // regular stack slots.
   auto InsBeforeB = InsBefore->getParent();
   assert(InsBeforeB == &F.getEntryBlock());
   for (auto *AI : StaticAllocasToMoveUp)
     if (AI->getParent() == InsBeforeB)
if (DoStackMalloc) {
     Constant *OptionDetectUseAfterReturn = F.getParent()->getOrInsertGlobal(
         kAsanOptionDetectUseAfterReturn, IRB.getInt32Ty());
     Value *UseAfterReturnIsEnabled = IRB.CreateICmpNE(
         IRB.CreateLoad(IRB.getInt32Ty(), OptionDetectUseAfterReturn),
         Constant::getNullValue(IRB.getInt32Ty()));
     Instruction *Term =
         SplitBlockAndInsertIfThen(UseAfterReturnIsEnabled, InsBefore, false);
     IRBuilder<> IRBIf(Term);
-    IRBIf.SetCurrentDebugLocation(EntryDebugLocation);
     StackMallocIdx = StackMallocSizeClass(LocalStackSize);
     assert(StackMallocIdx <= kMaxAsanStackMallocSizeClass);
     Value *FakeStackValue =
         IRBIf.CreateCall(AsanStackMallocFunc[StackMallocIdx],
                          ConstantInt::get(IntptrTy, LocalStackSize));
     IRB.SetInsertPoint(InsBefore);
-    IRB.SetCurrentDebugLocation(EntryDebugLocation);
     FakeStack = createPHI(IRB, UseAfterReturnIsEnabled, FakeStackValue, Term,
                           ConstantInt::get(IntptrTy, 0));
 
     Value *NoFakeStack =
         IRB.CreateICmpEQ(FakeStack, Constant::getNullValue(IntptrTy));
     Term = SplitBlockAndInsertIfThen(NoFakeStack, InsBefore, false);
     IRBIf.SetInsertPoint(Term);
-    IRBIf.SetCurrentDebugLocation(EntryDebugLocation);
     Value *AllocaValue =
         DoDynamicAlloca ? createAllocaForLayout(IRBIf, L, true) : StaticAlloca;
 
     IRB.SetInsertPoint(InsBefore);
-    IRB.SetCurrentDebugLocation(EntryDebugLocation);
     LocalStackBase = createPHI(IRB, NoFakeStack, AllocaValue, Term, FakeStack);
-    IRB.SetCurrentDebugLocation(EntryDebugLocation);
     IRB.CreateStore(LocalStackBase, LocalStackBaseAlloca);
     DIExprFlags |= DIExpression::DerefBefore;
   } else {
     // void *FakeStack = nullptr;
     // void *LocalStackBase = alloca(LocalStackSize);
     FakeStack = ConstantInt::get(IntptrTy, 0);
     LocalStackBase =
         DoDynamicAlloca ? createAllocaForLayout(IRB, L, true) : StaticAlloca;

llvm/test/Instrumentation/AddressSanitizer/debug-info-alloca.ll

+; Checks that asan instrumentation does not include line numbers as debug information.
+; Line info in an instrumentation instruction within the prologue would fool findPrologueEndLoc
+; to set the end of the prologue before that instruction. Breaking on the instrumented function
+; in the debugger would then stop there, before the prologue has finished.
+
+; RUN: opt < %s -asan -asan-module -S | FileCheck %s
+; 1: void f(int *arg) {
+; 2: }
+; 3: int main(int argc, char **argv) {
+; 4:   f(&argc);
+; 5: }
+; clang 1.cc -g -S -emit-llvm -o - | sed 's/#0 = {/#0 = { sanitize_address/'
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define dso_local i32 @main(i32 %argc, i8** %argv) #0 !dbg !15 {
+entry:
+; No suffix like !dbg !123
+; CHECK: %asan_local_stack_base = alloca i64{{$}}
+; CHECK:     %3 = call i64 @__asan_stack_malloc_0(i64 64){{$}}
+  %argc.addr = alloca i32, align 4
+  %argv.addr = alloca i8**, align 8
+  store i32 %argc, i32* %argc.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %argc.addr, metadata !21, metadata !DIExpression()), !dbg !22
+  store i8** %argv, i8*** %argv.addr, align 8
+  call void @llvm.dbg.declare(metadata i8*** %argv.addr, metadata !23, metadata !DIExpression()), !dbg !24
+  call void @f(i32* %argc.addr), !dbg !25
+  ret i32 0, !dbg !26
+}
+
+define dso_local void @f(i32* %arg) #0 !dbg !7 {
+entry:
+  %arg.addr = alloca i32*, align 8
+  store i32* %arg, i32** %arg.addr, align 8
+  call void @llvm.dbg.declare(metadata i32** %arg.addr, metadata !12, metadata !DIExpression()), !dbg !13
+  ret void, !dbg !14
+}
+
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+attributes #0 = { sanitize_address noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "frame-pointer"="all" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone speculatable willreturn }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 10.0.0 ([e-mail]:llvm/llvm-project 1ac700cdef787383ad49a0e37d9894491ef19480)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, nameTableKind: None)
+!1 = !DIFile(filename: "2.c", directory: "/home/builduser")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 10.0.0 ([e-mail]:llvm/llvm-project 1ac700cdef787383ad49a0e37d9894491ef19480)"}
+!7 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{null, !10}
+!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !11, size: 64)
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !DILocalVariable(name: "arg", arg: 1, scope: !7, file: !1, line: 1, type: !10)
+!13 = !DILocation(line: 1, column: 13, scope: !7)
+!14 = !DILocation(line: 2, column: 1, scope: !7)
+!15 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 3, type: !16, scopeLine: 3, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !2)
+!16 = !DISubroutineType(types: !17)
+!17 = !{!11, !11, !18}
+!18 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !19, size: 64)
+!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !20, size: 64)
+!20 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_signed_char)
+!21 = !DILocalVariable(name: "argc", arg: 1, scope: !15, file: !1, line: 3, type: !11)
+!22 = !DILocation(line: 3, column: 14, scope: !15)
+!23 = !DILocalVariable(name: "argv", arg: 2, scope: !15, file: !1, line: 3, type: !18)
+!24 = !DILocation(line: 3, column: 27, scope: !15)
+!25 = !DILocation(line: 4, column: 3, scope: !15)
+!26 = !DILocation(line: 5, column: 1, scope: !15)

llvm/test/Instrumentation/AddressSanitizer/local_stack_base.ll

 entry:
   %i.addr = alloca i32, align 4
   store i32 %i, i32* %i.addr, align 4
   call void @llvm.dbg.declare(metadata i32* %i.addr, metadata !12, metadata !DIExpression()), !dbg !13
 
   ; CHECK: %asan_local_stack_base = alloca i64
   ; CHECK: %[[ALLOCA:.*]] = ptrtoint i8* %MyAlloca to i64
   ; CHECK: %[[PHI:.*]] = phi i64 {{.*}} %[[ALLOCA]],
-  ; CHECK: store i64 %[[PHI]], i64* %asan_local_stack_base, !dbg
-  ; CHECK: call void @llvm.dbg.declare(metadata i64* %asan_local_stack_base, metadata !13, metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 32)), !dbg !14
+  ; CHECK: store i64 %[[PHI]], i64* %asan_local_stack_base
+  ; CHECK: call void @llvm.dbg.declare(metadata i64* %asan_local_stack_base, metadata !12, metadata !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 32)), !dbg !13
   %0 = load i32, i32* %i.addr, align 4, !dbg !14
   %add = add nsw i32 %0, 2, !dbg !15
   ret i32 %add, !dbg !16
 }
 
 ; Function Attrs: nounwind readnone speculatable
 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1