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

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The function stack poisioner conditionally stores local variables
either in an alloca or in malloc'ated memory, which has the
unfortunate side-effect, that the actual address of the variable is
only materialized when the variable is accessed, which means that
those variables are mostly invisible to the debugger even when
compiling without optimizations.

This patch stores the address of the local stack base into an alloca,
which can be referred to by the debug info and is available throughout
the function. This adds one extra pointer-sized alloca to each stack
frame (but mem2reg can optimize it away again when optimizations are
enabled, yielding roughly the same debug info quality as before in
optimized code).

rdar://problem/30433661

Differential Revision: https://reviews.llvm.org/D41034

llvm-svn: 320415
This commit is contained in:
Adrian Prantl 2017-12-11 20:43:21 +00:00
parent 297ca0894d
commit 5ae8c3d77e
6 changed files with 73 additions and 5 deletions
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14
lib/Transforms/Instrumentation/AddressSanitizer.cpp
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@ -2869,8 +2869,12 @@ void FunctionStackPoisoner::processStaticAllocas() {
Value *FakeStack;
Value *LocalStackBase;
Value *LocalStackBaseAlloca;
bool Deref;
if (DoStackMalloc) {
LocalStackBaseAlloca =
IRB.CreateAlloca(IntptrTy, nullptr, "asan_local_stack_base");
// void *FakeStack = __asan_option_detect_stack_use_after_return
// ? __asan_stack_malloc_N(LocalStackSize)
// : nullptr;
@ -2901,25 +2905,31 @@ void FunctionStackPoisoner::processStaticAllocas() {
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);
Deref = true;
} else {
// void *FakeStack = nullptr;
// void *LocalStackBase = alloca(LocalStackSize);
FakeStack = ConstantInt::get(IntptrTy, 0);
LocalStackBase =
DoDynamicAlloca ? createAllocaForLayout(IRB, L, true) : StaticAlloca;
LocalStackBaseAlloca = LocalStackBase;
Deref = false;
}
// Replace Alloca instructions with base+offset.
for (const auto &Desc : SVD) {
AllocaInst *AI = Desc.AI;
replaceDbgDeclareForAlloca(AI, LocalStackBaseAlloca, DIB, Deref,
Desc.Offset, DIExpression::NoDeref);
Value *NewAllocaPtr = IRB.CreateIntToPtr(
IRB.CreateAdd(LocalStackBase, ConstantInt::get(IntptrTy, Desc.Offset)),
AI->getType());
replaceDbgDeclareForAlloca(AI, NewAllocaPtr, DIB, DIExpression::NoDeref,
0, DIExpression::NoDeref);
AI->replaceAllUsesWith(NewAllocaPtr);
}

2
test/DebugInfo/Generic/block-asan.ll
View File

@ -13,7 +13,7 @@
; Check that the location of the ASAN instrumented __block variable is
; correct.
; CHECK: !DIExpression(DW_OP_plus_uconst, 8, DW_OP_deref, DW_OP_plus_uconst, 24)
; CHECK: !DIExpression(DW_OP_deref, DW_OP_plus_uconst, 32, DW_OP_plus_uconst, 8, DW_OP_deref, DW_OP_plus_uconst, 24)
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"

1
test/Instrumentation/AddressSanitizer/basic.ll
View File

@ -91,6 +91,7 @@ entry:
}
; CHECK-LABEL: define void @alloca_test()
; CHECK: %asan_local_stack_base = alloca
; CHECK: = alloca
; CHECK-NOT: = alloca
; CHECK: ret void

4
test/Instrumentation/AddressSanitizer/debug_info.ll
View File

@ -24,9 +24,9 @@ entry:
; CHECK: entry:
; Verify that llvm.dbg.declare calls are in the entry basic block.
; CHECK-NOT: %entry
; CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[ARG_ID:[0-9]+]], metadata !DIExpression())
; CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[ARG_ID:[0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 32))
; CHECK-NOT: %entry
; CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[VAR_ID:[0-9]+]], metadata !DIExpression())
; CHECK: call void @llvm.dbg.declare(metadata {{.*}}, metadata ![[VAR_ID:[0-9]+]], metadata !DIExpression(DW_OP_plus_uconst, 48))
declare void @llvm.dbg.declare(metadata, metadata, metadata) nounwind readnone

54
test/Instrumentation/AddressSanitizer/local_stack_base.ll Normal file
View File

@ -0,0 +1,54 @@
; RUN: opt -S -asan -asan-skip-promotable-allocas=0 %s -o - | FileCheck %s
; Generated from:
; int bar(int y) {
; return y + 2;
; }
source_filename = "/tmp/t.c"
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx10.13.0"
; Function Attrs: noinline nounwind optnone sanitize_address ssp uwtable
define i32 @foo(i32 %i) #0 !dbg !8 {
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
%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
attributes #0 = { noinline nounwind optnone sanitize_address ssp uwtable }
attributes #1 = { nounwind readnone speculatable }
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!3, !4, !5, !6}
!llvm.ident = !{!7}
!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 6.0.0 (trunk 320115) (llvm/trunk 320116)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
!1 = !DIFile(filename: "/tmp/t.c", directory: "/Data/llvm")
!2 = !{}
!3 = !{i32 2, !"Dwarf Version", i32 4}
!4 = !{i32 2, !"Debug Info Version", i32 3}
!5 = !{i32 1, !"wchar_size", i32 4}
!6 = !{i32 7, !"PIC Level", i32 2}
!7 = !{!"clang version 6.0.0 (trunk 320115) (llvm/trunk 320116)"}
!8 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !9, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
!9 = !DISubroutineType(types: !10)
!10 = !{!11, !11}
!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
!12 = !DILocalVariable(name: "i", arg: 1, scope: !8, file: !1, line: 1, type: !11)
!13 = !DILocation(line: 1, column: 13, scope: !8)
!14 = !DILocation(line: 2, column: 10, scope: !8)
!15 = !DILocation(line: 2, column: 12, scope: !8)
!16 = !DILocation(line: 2, column: 3, scope: !8)

3
test/Instrumentation/AddressSanitizer/stack_layout.ll
View File

@ -22,6 +22,7 @@ entry:
; CHECK-LABEL: Func1
; CHECK-STATIC: alloca [192 x i8]
; CHECK-STATIC: %asan_local_stack_base = alloca i64
; CHECK-DYNAMIC: alloca i8, i64 192
; CHECK-NOT: alloca
@ -43,6 +44,7 @@ entry:
; CHECK-LABEL: Func2
; CHECK-STATIC: alloca [864 x i8]
; CHECK-STATIC: %asan_local_stack_base = alloca i64
; CHECK-DYNAMIC: alloca i8, i64 864
; CHECK-NOT: alloca
@ -65,6 +67,7 @@ entry:
; CHECK-LABEL: Func3
; CHECK-STATIC: alloca [768 x i8]
; CHECK-STATIC: %asan_local_stack_base = alloca i64
; CHECK-DYNAMIC: alloca i8, i64 768
; CHECK-NOT: alloca