[llvm] 39e8137 - [NFC] [HWASan] add example for ring buffer wrap (#87029)
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Thu Mar 28 18:23:51 PDT 2024
Author: Florian Mayer
Date: 2024-03-28T18:23:48-07:00
New Revision: 39e813746730a83e49b7efc457ff7efc74925c74
URL: https://github.com/llvm/llvm-project/commit/39e813746730a83e49b7efc457ff7efc74925c74
DIFF: https://github.com/llvm/llvm-project/commit/39e813746730a83e49b7efc457ff7efc74925c74.diff
LOG: [NFC] [HWASan] add example for ring buffer wrap (#87029)
Also another move comment to correct place.
Added:
Modified:
llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
index f7d4803ded155a..d0d349c891a37b 100644
--- a/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -1114,8 +1114,6 @@ void HWAddressSanitizer::tagAlloca(IRBuilder<> &IRB, AllocaInst *AI, Value *Tag,
// FIXME: the interceptor is not as fast as real memset. Consider lowering
// llvm.memset right here into either a sequence of stores, or a call to
// hwasan_tag_memory.
- // Mechanical proof of this address calculation can be found at:
- // https://github.com/google/sanitizers/blob/master/hwaddress-sanitizer/prove_hwasanwrap.smt2
if (ShadowSize)
IRB.CreateMemSet(ShadowPtr, Tag, ShadowSize, Align(1));
if (Size != AlignedSize) {
@@ -1312,6 +1310,22 @@ void HWAddressSanitizer::emitPrologue(IRBuilder<> &IRB, bool WithFrameRecord) {
// The use of AShr instead of LShr is due to
// https://bugs.llvm.org/show_bug.cgi?id=39030
// Runtime library makes sure not to use the highest bit.
+ //
+ // Mechanical proof of this address calculation can be found at:
+ // https://github.com/google/sanitizers/blob/master/hwaddress-sanitizer/prove_hwasanwrap.smt2
+ //
+ // Example of the wrap case for N = 1
+ // Pointer: 0x01AAAAAAAAAAAFF8
+ // +
+ // 0x0000000000000008
+ // =
+ // 0x01AAAAAAAAAAB000
+ // &
+ // WrapMask: 0xFFFFFFFFFFFFF000
+ // =
+ // 0x01AAAAAAAAAAA000
+ //
+ // Then the WrapMask will be a no-op until the next wrap case.
Value *WrapMask = IRB.CreateXor(
IRB.CreateShl(IRB.CreateAShr(ThreadLong, 56), 12, "", true, true),
ConstantInt::get(IntptrTy, (uint64_t)-1));
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