Fix Endianess issue

[anoopkg6]

Fix Endianess issue with getting shadow 4 bytes corresponding to the first origin pointer.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (anoopkg6)

Changes

Fix Endianess issue with getting shadow 4 bytes corresponding to the first origin pointer.

---

Full diff: https://github.com/llvm/llvm-project/pull/162881.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp (+8-2)

diff --git a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
index 5ba2167859490..b4f88779b00c0 100644
--- a/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp
@@ -2187,8 +2187,14 @@ std::pair<Value *, Value *> DFSanFunction::loadShadowFast(
       // and then the entire shadow for the second origin pointer (which will be
       // chosen by combineOrigins() iff the least-significant half of the wide
       // shadow was empty but the other half was not).
-      Value *WideShadowLo = IRB.CreateShl(
-          WideShadow, ConstantInt::get(WideShadowTy, WideShadowBitWidth / 2));
+      Value *WideShadowLo =
+          F->getParent()->getDataLayout().isLittleEndian()
+              ? IRB.CreateShl(
+                    WideShadow,
+                    ConstantInt::get(WideShadowTy, WideShadowBitWidth / 2))
+              : IRB.CreateAnd(
+                    WideShadow,
+                    ConstantInt::get(WideShadowTy, 0xFFFFFFFF00000000ULL));
       Shadows.push_back(WideShadow);
       Origins.push_back(DFS.loadNextOrigin(Pos, OriginAlign, &OriginAddr));
 

[thurstond]

Please add "[dfsan]" to the title

[thurstond]

Can this be rewritten in terms of WideShadowBitWidth?

(I think it's something like (1 - (1 << (WideShadowBitWidth / 2))) << (WideShadowBitWidth / 2))

[vitalybuka]

I don't believe we support other that little endian. So there is no point to complicate code for that.

[thurstond]

I don't believe we support other that little endian. So there is no point to complicate code for that.

They are adding support for SystemZ (#162195).

[thurstond]

Also, RISC-V has an exciting big-endian extension (/cc @fmayer)

[vitalybuka]

I don't believe we support other that little endian. So there is no point to complicate code for that.

They are adding support for SystemZ (#162195).

Is #162195 enough?
I'd expect sanitizers does a lot of assumptions on little-endianness.