[HLSL] Prevent uninitialized on 2 int arguments

[Keenuts]

Unparsed HLSL semantics have 2 int/bool arguments with default values. Those values are loaded using checkUInt32Argument, and thus this should never fail.

But if something is wrong in the code above (or the def changed), this code wouldn't catch it and we'd read uninitialized integers. This commits checks both return values and assert if one fails. On release builds, this would early return, causing a bad codegen, but such change will be caught by tests.

[llvmbot]

@llvm/pr-subscribers-hlsl

@llvm/pr-subscribers-clang

Author: Nathan Gauër (Keenuts)

Changes

Unparsed HLSL semantics have 2 int/bool arguments with default values. Those values are loaded using checkUInt32Argument, and thus this should never fail.

But if something is wrong in the code above (or the def changed), this code wouldn't catch it and we'd read uninitialized integers. This commits checks both return values and assert if one fails. On release builds, this would early return, causing a bad codegen, but such change will be caught by tests.

---

Full diff: https://github.com/llvm/llvm-project/pull/173352.diff

1 Files Affected:

• (modified) clang/lib/Sema/SemaHLSL.cpp (+5-3)

diff --git a/clang/lib/Sema/SemaHLSL.cpp b/clang/lib/Sema/SemaHLSL.cpp
index 06130c985876f..0b1996b4789d6 100644
--- a/clang/lib/Sema/SemaHLSL.cpp
+++ b/clang/lib/Sema/SemaHLSL.cpp
@@ -1908,9 +1908,11 @@ void SemaHLSL::diagnoseSystemSemanticAttr(Decl *D, const ParsedAttr &AL,
 }
 
 void SemaHLSL::handleSemanticAttr(Decl *D, const ParsedAttr &AL) {
-  uint32_t IndexValue, ExplicitIndex;
-  SemaRef.checkUInt32Argument(AL, AL.getArgAsExpr(0), IndexValue);
-  SemaRef.checkUInt32Argument(AL, AL.getArgAsExpr(1), ExplicitIndex);
+  uint32_t IndexValue(0), ExplicitIndex(0);
+  if (!SemaRef.checkUInt32Argument(AL, AL.getArgAsExpr(0), IndexValue) ||
+      !SemaRef.checkUInt32Argument(AL, AL.getArgAsExpr(1), ExplicitIndex)) {
+    assert(0 && "HLSLUnparsedSemantic is expected to have 2 int arguments.");
+  }
   assert(IndexValue > 0 ? ExplicitIndex : true);
   std::optional<unsigned> Index =
       ExplicitIndex ? std::optional<unsigned>(IndexValue) : std::nullopt;