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

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

6 files changed, 73 insertions, 5 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index f626c2c0b16..8328d403194 100644
--- a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -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);
   }
 
diff --git a/llvm/test/DebugInfo/Generic/block-asan.ll b/llvm/test/DebugInfo/Generic/block-asan.ll
index 73df59bf3d5..c3f71e742b2 100644
--- a/llvm/test/DebugInfo/Generic/block-asan.ll
+++ b/llvm/test/DebugInfo/Generic/block-asan.ll
@@ -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"
 
diff --git a/llvm/test/Instrumentation/AddressSanitizer/basic.ll b/llvm/test/Instrumentation/AddressSanitizer/basic.ll
index 2385341387d..f684f9927fa 100644
--- a/llvm/test/Instrumentation/AddressSanitizer/basic.ll
+++ b/llvm/test/Instrumentation/AddressSanitizer/basic.ll
@@ -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
diff --git a/llvm/test/Instrumentation/AddressSanitizer/debug_info.ll b/llvm/test/Instrumentation/AddressSanitizer/debug_info.ll
index 37829b0053f..544082d0da3 100644
--- a/llvm/test/Instrumentation/AddressSanitizer/debug_info.ll
+++ b/llvm/test/Instrumentation/AddressSanitizer/debug_info.ll
@@ -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
 
diff --git a/llvm/test/Instrumentation/AddressSanitizer/local_stack_base.ll b/llvm/test/Instrumentation/AddressSanitizer/local_stack_base.ll
new file mode 100644
index 00000000000..f440410599e
--- /dev/null
+++ b/llvm/test/Instrumentation/AddressSanitizer/local_stack_base.ll
@@ -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)
diff --git a/llvm/test/Instrumentation/AddressSanitizer/stack_layout.ll b/llvm/test/Instrumentation/AddressSanitizer/stack_layout.ll
index 4e756f9ab2f..85169d523b6 100644
--- a/llvm/test/Instrumentation/AddressSanitizer/stack_layout.ll
+++ b/llvm/test/Instrumentation/AddressSanitizer/stack_layout.ll
@@ -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