[llvm-branch-commits] [compiler-rt] [TySan] Fix struct access with different bases (PR #108385)

[via llvm-branch-commits]

https://github.com/gbMattN updated https://github.com/llvm/llvm-project/pull/108385

>From 65f1e1fce67bfc9ae60f83abe6d3b487a174c6b1 Mon Sep 17 00:00:00 2001
From: Matthew Nagy <gbmatt at tiger-linux2.domain.snsys.com>
Date: Thu, 12 Sep 2024 12:36:57 +0000
Subject: [PATCH] [TySan] Fix struct access with different bases

---
 compiler-rt/lib/tysan/tysan.cpp               |  4 +++
 .../tysan/struct-offset-different-base.cpp    | 31 +++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 compiler-rt/test/tysan/struct-offset-different-base.cpp

diff --git a/compiler-rt/lib/tysan/tysan.cpp b/compiler-rt/lib/tysan/tysan.cpp
index f627851d049e6a..f2cb6faddf45ac 100644
--- a/compiler-rt/lib/tysan/tysan.cpp
+++ b/compiler-rt/lib/tysan/tysan.cpp
@@ -128,6 +128,10 @@ static bool isAliasingLegalUp(tysan_type_descriptor *TDA,
           break;
       }
 
+      //You can't have negative offset, you must be partially inside the last type
+      if (TDA->Struct.Members[Idx].Offset > OffsetA)
+        Idx -=1;
+        
       OffsetA -= TDA->Struct.Members[Idx].Offset;
       TDA = TDA->Struct.Members[Idx].Type;
     } else {
diff --git a/compiler-rt/test/tysan/struct-offset-different-base.cpp b/compiler-rt/test/tysan/struct-offset-different-base.cpp
new file mode 100644
index 00000000000000..716d21f844f96c
--- /dev/null
+++ b/compiler-rt/test/tysan/struct-offset-different-base.cpp
@@ -0,0 +1,31 @@
+// RUN: %clangxx_tysan -O0 %s -o %t && %run %t >%t.out 2>&1
+// RUN: FileCheck %s < %t.out
+
+#include <stdio.h>
+
+struct inner {
+	char buffer;
+	int i;
+};
+
+void init_inner(inner *iPtr) {
+	iPtr->i = 0;
+}
+
+struct outer {
+	inner foo;
+    char buffer;
+};
+
+int main(void) {
+    outer *l = new outer();
+
+    init_inner(&l->foo);
+    
+    int access_offsets_with_different_base = l->foo.i;
+    printf("%d\n", access_offsets_with_different_base);
+    
+    return 0;
+}
+
+// CHECK-NOT: ERROR: TypeSanitizer: type-aliasing-violation