[UBSAN] add null and alignment checks for aggregates

[vasu-the-sharma]

Description

This PR adds sanitizer checks for null pointers and misalignment during aggregate copy operations in EmitAggregateCopy.

Current State

When copying aggregates (structs), the compiler does not validate that source and destination pointers are non-null or properly aligned when sanitizers are enabled. This allows undefined behavior from invalid pointers to go undetected at runtime.

Solution

When null or alignment sanitizers are active, this change:

• Retrieves raw pointer addresses from both source and destination LValues
• Performs EmitTypeCheck on both pointers to verify they are non-null and meet alignment requirements
• Records these checks in the SanitizerSet for runtime emission

This ensures memory safety violations are caught early, preventing crashes and corruption from invalid aggregate copies.

Testing

Added comprehensive test cases covering:

• Null source pointer detection
• Null destination pointer detection
• Misaligned source pointer detection
• Misaligned destination pointer detection
• Normal copy operations (no false positives)

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[llvmbot]

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

@llvm/pr-subscribers-clang

Author: VASU SHARMA (vasu-the-sharma)

Changes

This PR adds null and alignment checks for aggregates like scalars

---

Full diff: https://github.com/llvm/llvm-project/pull/164548.diff

1 Files Affected:

• (modified) clang/lib/CodeGen/CGExprAgg.cpp (+15)

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index eee397f1f3d19..de6d80a273dbd 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -2249,6 +2249,21 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
                                         bool isVolatile) {
   assert(!Ty->isAnyComplexType() && "Shouldn't happen for complex");
 
+  if (SanOpts.hasOneOf(SanitizerKind::Null | SanitizerKind::Alignment)) {
+    Address SrcAddr = Src.getAddress();
+    Address DestAddr = Dest.getAddress();
+
+    // Check source pointer for null and alignment violations
+    EmitTypeCheck(TCK_Load, SourceLocation(),
+                  SrcAddr.emitRawPointer(*this), Ty, SrcAddr.getAlignment(),
+                  SanitizerSet());
+
+    // Check destination pointer for null and alignment violations
+    EmitTypeCheck(TCK_Store, SourceLocation(),
+                  DestAddr.emitRawPointer(*this), Ty, DestAddr.getAlignment(),
+                  SanitizerSet());
+  }
+
   Address DestPtr = Dest.getAddress();
   Address SrcPtr = Src.getAddress();
 

[github-actions]

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff origin/main HEAD --extensions cpp -- clang/lib/CodeGen/CGExprAgg.cpp --diff_from_common_commit

⚠️
The reproduction instructions above might return results for more than one PR
in a stack if you are using a stacked PR workflow. You can limit the results by
changing origin/main to the base branch/commit you want to compare against.
⚠️

View the diff from clang-format here.

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index de6d80a27..1d6e3c101 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -2254,14 +2254,12 @@ void CodeGenFunction::EmitAggregateCopy(LValue Dest, LValue Src, QualType Ty,
     Address DestAddr = Dest.getAddress();
 
     // Check source pointer for null and alignment violations
-    EmitTypeCheck(TCK_Load, SourceLocation(),
-                  SrcAddr.emitRawPointer(*this), Ty, SrcAddr.getAlignment(),
-                  SanitizerSet());
+    EmitTypeCheck(TCK_Load, SourceLocation(), SrcAddr.emitRawPointer(*this), Ty,
+                  SrcAddr.getAlignment(), SanitizerSet());
 
     // Check destination pointer for null and alignment violations
-    EmitTypeCheck(TCK_Store, SourceLocation(),
-                  DestAddr.emitRawPointer(*this), Ty, DestAddr.getAlignment(),
-                  SanitizerSet());
+    EmitTypeCheck(TCK_Store, SourceLocation(), DestAddr.emitRawPointer(*this),
+                  Ty, DestAddr.getAlignment(), SanitizerSet());
   }
 
   Address DestPtr = Dest.getAddress();

[tonykuttai]

Please add a test support this change

[tonykuttai]

Can you add comment block here to explain

• why we need this if block
• what is it doing.?

[hubert-reinterpretcast]

I believe there should be a Clang CodeGen test for this.

[hubert-reinterpretcast]

I think the scope should be expanded to other cases covered by EmitCheckedLValue.

[hubert-reinterpretcast]

I recommend omitting this check and leaving sanitizePerformTypeCheck to do its work.