hwasan: Move memory access checks into small outlined functions on aarch64.

Each hwasan check requires emitting a small piece of code like this:
https://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html#memory-accesses

The problem with this is that these code blocks typically bloat code
size significantly.

An obvious solution is to outline these blocks of code. In fact, this
has already been implemented under the -hwasan-instrument-with-calls
flag. However, as currently implemented this has a number of problems:
- The functions use the same calling convention as regular C functions.
  This means that the backend must spill all temporary registers as
  required by the platform's C calling convention, even though the
  check only needs two registers on the hot path.
- The functions take the address to be checked in a fixed register,
  which increases register pressure.
Both of these factors can diminish the code size effect and increase
the performance hit of -hwasan-instrument-with-calls.

The solution that this patch implements is to involve the aarch64
backend in outlining the checks. An intrinsic and pseudo-instruction
are created to represent a hwasan check. The pseudo-instruction
is register allocated like any other instruction, and we allow the
register allocator to select almost any register for the address to
check. A particular combination of (register selection, type of check)
triggers the creation in the backend of a function to handle the check
for specifically that pair. The resulting functions are deduplicated by
the linker. The pseudo-instruction (really the function) is specified
to preserve all registers except for the registers that the AAPCS
specifies may be clobbered by a call.

To measure the code size and performance effect of this change, I
took a number of measurements using Chromium for Android on aarch64,
comparing a browser with inlined checks (the baseline) against a
browser with outlined checks.

Code size: Size of .text decreases from 243897420 to 171619972 bytes,
or a 30% decrease.

Performance: Using Chromium's blink_perf.layout microbenchmarks I
measured a median performance regression of 6.24%.

The fact that a perf/size tradeoff is evident here suggests that
we might want to make the new behaviour conditional on -Os/-Oz.
But for now I've enabled it unconditionally, my reasoning being that
hwasan users typically expect a relatively large perf hit, and ~6%
isn't really adding much. We may want to revisit this decision in
the future, though.

I also tried experimenting with varying the number of registers
selectable by the hwasan check pseudo-instruction (which would result
in fewer variants being created), on the hypothesis that creating
fewer variants of the function would expose another perf/size tradeoff
by reducing icache pressure from the check functions at the cost of
register pressure. Although I did observe a code size increase with
fewer registers, I did not observe a strong correlation between the
number of registers and the performance of the resulting browser on the
microbenchmarks, so I conclude that we might as well use ~all registers
to get the maximum code size improvement. My results are below:

Regs | .text size | Perf hit
-----+------------+---------
~all | 171619972  | 6.24%
  16 | 171765192  | 7.03%
   8 | 172917788  | 5.82%
   4 | 177054016  | 6.89%

Differential Revision: https://reviews.llvm.org/D56954

llvm-svn: 351920

1 files changed, 45 insertions, 24 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
index 5d10d57dc44..a00070e34aa 100644
--- a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -155,6 +155,11 @@ static cl::opt<bool>
     ClInstrumentMemIntrinsics("hwasan-instrument-mem-intrinsics",
                               cl::desc("instrument memory intrinsics"),
                               cl::Hidden, cl::init(true));
+
+static cl::opt<bool> ClInlineAllChecks("hwasan-inline-all-checks",
+                                       cl::desc("inline all checks"),
+                                       cl::Hidden, cl::init(false));
+
 namespace {
 
 /// An instrumentation pass implementing detection of addressability bugs
@@ -181,8 +186,9 @@ public:
   Value *getDynamicShadowNonTls(IRBuilder<> &IRB);
 
   void untagPointerOperand(Instruction *I, Value *Addr);
-  Value *memToShadow(Value *Shadow, Type *Ty, IRBuilder<> &IRB);
-  void instrumentMemAccessInline(Value *PtrLong, bool IsWrite,
+  Value *shadowBase();
+  Value *memToShadow(Value *Shadow, IRBuilder<> &IRB);
+  void instrumentMemAccessInline(Value *Ptr, bool IsWrite,
                                  unsigned AccessSizeIndex,
                                  Instruction *InsertBefore);
   void instrumentMemIntrinsic(MemIntrinsic *MI);
@@ -252,6 +258,7 @@ private:
   Type *IntptrTy;
   Type *Int8PtrTy;
   Type *Int8Ty;
+  Type *Int32Ty;
 
   bool CompileKernel;
   bool Recover;
@@ -307,6 +314,7 @@ bool HWAddressSanitizer::doInitialization(Module &M) {
   IntptrTy = IRB.getIntPtrTy(DL);
   Int8PtrTy = IRB.getInt8PtrTy();
   Int8Ty = IRB.getInt8Ty();
+  Int32Ty = IRB.getInt32Ty();
 
   HwasanCtorFunction = nullptr;
   if (!CompileKernel) {
@@ -403,16 +411,16 @@ Value *HWAddressSanitizer::getDynamicShadowNonTls(IRBuilder<> &IRB) {
 
   if (Mapping.InGlobal) {
     // An empty inline asm with input reg == output reg.
-    // An opaque pointer-to-int cast, basically.
+    // An opaque no-op cast, basically.
     InlineAsm *Asm = InlineAsm::get(
-        FunctionType::get(IntptrTy, {ShadowGlobal->getType()}, false),
+        FunctionType::get(Int8PtrTy, {ShadowGlobal->getType()}, false),
         StringRef(""), StringRef("=r,0"),
         /*hasSideEffects=*/false);
     return IRB.CreateCall(Asm, {ShadowGlobal}, ".hwasan.shadow");
   } else {
     Value *GlobalDynamicAddress =
         IRB.GetInsertBlock()->getParent()->getParent()->getOrInsertGlobal(
-            kHwasanShadowMemoryDynamicAddress, IntptrTy);
+            kHwasanShadowMemoryDynamicAddress, Int8PtrTy);
     return IRB.CreateLoad(GlobalDynamicAddress);
   }
 }
@@ -505,29 +513,44 @@ void HWAddressSanitizer::untagPointerOperand(Instruction *I, Value *Addr) {
   I->setOperand(getPointerOperandIndex(I), UntaggedPtr);
 }
 
-Value *HWAddressSanitizer::memToShadow(Value *Mem, Type *Ty, IRBuilder<> &IRB) {
+Value *HWAddressSanitizer::shadowBase() {
+  if (LocalDynamicShadow)
+    return LocalDynamicShadow;
+  return ConstantExpr::getIntToPtr(ConstantInt::get(IntptrTy, Mapping.Offset),
+                                   Int8PtrTy);
+}
+
+Value *HWAddressSanitizer::memToShadow(Value *Mem, IRBuilder<> &IRB) {
   // Mem >> Scale
   Value *Shadow = IRB.CreateLShr(Mem, Mapping.Scale);
   if (Mapping.Offset == 0)
-    return Shadow;
+    return IRB.CreateIntToPtr(Shadow, Int8PtrTy);
   // (Mem >> Scale) + Offset
-  Value *ShadowBase;
-  if (LocalDynamicShadow)
-    ShadowBase = LocalDynamicShadow;
-  else
-    ShadowBase = ConstantInt::get(Ty, Mapping.Offset);
-  return IRB.CreateAdd(Shadow, ShadowBase);
+  return IRB.CreateGEP(Int8Ty, shadowBase(), Shadow);
 }
 
-void HWAddressSanitizer::instrumentMemAccessInline(Value *PtrLong, bool IsWrite,
+void HWAddressSanitizer::instrumentMemAccessInline(Value *Ptr, bool IsWrite,
                                                    unsigned AccessSizeIndex,
                                                    Instruction *InsertBefore) {
+  const int64_t AccessInfo = Recover * 0x20 + IsWrite * 0x10 + AccessSizeIndex;
   IRBuilder<> IRB(InsertBefore);
+
+  if (!ClInlineAllChecks && TargetTriple.isAArch64() &&
+      TargetTriple.isOSBinFormatELF() && !Recover) {
+    Module *M = IRB.GetInsertBlock()->getParent()->getParent();
+    Ptr = IRB.CreateBitCast(Ptr, Int8PtrTy);
+    IRB.CreateCall(
+        Intrinsic::getDeclaration(M, Intrinsic::hwasan_check_memaccess),
+        {shadowBase(), Ptr, ConstantInt::get(Int32Ty, AccessInfo)});
+    return;
+  }
+
+  Value *PtrLong = IRB.CreatePointerCast(Ptr, IntptrTy);
   Value *PtrTag = IRB.CreateTrunc(IRB.CreateLShr(PtrLong, kPointerTagShift),
                                   IRB.getInt8Ty());
   Value *AddrLong = untagPointer(IRB, PtrLong);
-  Value *ShadowLong = memToShadow(AddrLong, PtrLong->getType(), IRB);
-  Value *MemTag = IRB.CreateLoad(IRB.CreateIntToPtr(ShadowLong, Int8PtrTy));
+  Value *Shadow = memToShadow(AddrLong, IRB);
+  Value *MemTag = IRB.CreateLoad(Shadow);
   Value *TagMismatch = IRB.CreateICmpNE(PtrTag, MemTag);
 
   int matchAllTag = ClMatchAllTag.getNumOccurrences() > 0 ?
@@ -543,7 +566,6 @@ void HWAddressSanitizer::instrumentMemAccessInline(Value *PtrLong, bool IsWrite,
                                 MDBuilder(*C).createBranchWeights(1, 100000));
 
   IRB.SetInsertPoint(CheckTerm);
-  const int64_t AccessInfo = Recover * 0x20 + IsWrite * 0x10 + AccessSizeIndex;
   InlineAsm *Asm;
   switch (TargetTriple.getArch()) {
     case Triple::x86_64:
@@ -609,7 +631,6 @@ bool HWAddressSanitizer::instrumentMemAccess(Instruction *I) {
     return false; //FIXME
 
   IRBuilder<> IRB(I);
-  Value *AddrLong = IRB.CreatePointerCast(Addr, IntptrTy);
   if (isPowerOf2_64(TypeSize) &&
       (TypeSize / 8 <= (1UL << (kNumberOfAccessSizes - 1))) &&
       (Alignment >= (1UL << Mapping.Scale) || Alignment == 0 ||
@@ -617,13 +638,14 @@ bool HWAddressSanitizer::instrumentMemAccess(Instruction *I) {
     size_t AccessSizeIndex = TypeSizeToSizeIndex(TypeSize);
     if (ClInstrumentWithCalls) {
       IRB.CreateCall(HwasanMemoryAccessCallback[IsWrite][AccessSizeIndex],
-                     AddrLong);
+                     IRB.CreatePointerCast(Addr, IntptrTy));
     } else {
-      instrumentMemAccessInline(AddrLong, IsWrite, AccessSizeIndex, I);
+      instrumentMemAccessInline(Addr, IsWrite, AccessSizeIndex, I);
     }
   } else {
     IRB.CreateCall(HwasanMemoryAccessCallbackSized[IsWrite],
-                   {AddrLong, ConstantInt::get(IntptrTy, TypeSize / 8)});
+                   {IRB.CreatePointerCast(Addr, IntptrTy),
+                    ConstantInt::get(IntptrTy, TypeSize / 8)});
   }
   untagPointerOperand(I, Addr);
 
@@ -654,9 +676,7 @@ bool HWAddressSanitizer::tagAlloca(IRBuilder<> &IRB, AllocaInst *AI,
                     ConstantInt::get(IntptrTy, Size)});
   } else {
     size_t ShadowSize = Size >> Mapping.Scale;
-    Value *ShadowPtr = IRB.CreateIntToPtr(
-        memToShadow(IRB.CreatePointerCast(AI, IntptrTy), AI->getType(), IRB),
-        Int8PtrTy);
+    Value *ShadowPtr = memToShadow(IRB.CreatePointerCast(AI, IntptrTy), IRB);
     // If this memset is not inlined, it will be intercepted in the hwasan
     // runtime library. That's OK, because the interceptor skips the checks if
     // the address is in the shadow region.
@@ -883,6 +903,7 @@ Value *HWAddressSanitizer::emitPrologue(IRBuilder<> &IRB,
           ThreadLongMaybeUntagged,
           ConstantInt::get(IntptrTy, (1ULL << kShadowBaseAlignment) - 1)),
       ConstantInt::get(IntptrTy, 1), "hwasan.shadow");
+  ShadowBase = IRB.CreateIntToPtr(ShadowBase, Int8PtrTy);
   return ShadowBase;
 }