[clang] [clang][bytecode] Check memcmp builtin for one-past-the-end pointers (PR #170097)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Timm Baeder (tbaederr)

<details>
<summary>Changes</summary>

We can't read from those and will run into an assertion sooner or later.

Fixes https://github.com/llvm/llvm-project/issues/170031

---
Full diff: https://github.com/llvm/llvm-project/pull/170097.diff


2 Files Affected:

- (modified) clang/lib/AST/ByteCode/InterpBuiltin.cpp (+4) 
- (modified) clang/test/AST/ByteCode/builtin-functions.cpp (+7) 


``````````diff
diff --git a/clang/lib/AST/ByteCode/InterpBuiltin.cpp b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
index 8496b58105c7a..971fce541bb88 100644
--- a/clang/lib/AST/ByteCode/InterpBuiltin.cpp
+++ b/clang/lib/AST/ByteCode/InterpBuiltin.cpp
@@ -1921,6 +1921,10 @@ static bool interp__builtin_memcmp(InterpState &S, CodePtr OpPC,
   if (PtrA.isDummy() || PtrB.isDummy())
     return false;
 
+  if (!CheckRange(S, OpPC, PtrA, AK_Read) ||
+      !CheckRange(S, OpPC, PtrB, AK_Read))
+    return false;
+
   // Now, read both pointers to a buffer and compare those.
   BitcastBuffer BufferA(
       Bits(ASTCtx.getTypeSize(ElemTypeA) * PtrA.getNumElems()));
diff --git a/clang/test/AST/ByteCode/builtin-functions.cpp b/clang/test/AST/ByteCode/builtin-functions.cpp
index 4a53cb66b2fdd..3076b5239ebbe 100644
--- a/clang/test/AST/ByteCode/builtin-functions.cpp
+++ b/clang/test/AST/ByteCode/builtin-functions.cpp
@@ -1545,6 +1545,13 @@ namespace Memcmp {
 
   int unknown;
   void foo(void) { unknown *= __builtin_memcmp(0, 0, 2); }
+
+  constexpr int onepasttheend(char a) {
+    __builtin_memcmp(&a, &a + 1, 1); // both-note {{read of dereferenced one-past-the-end pointer}}
+    return 1;
+  }
+  static_assert(onepasttheend(10)); // both-error {{not an integral constant expression}} \
+                                    // both-note {{in call to}}
 }
 
 namespace Memchr {

``````````

</details>


https://github.com/llvm/llvm-project/pull/170097