[libc-commits] [libc] [libc] Fix UB in memory utils (PR #74295)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Guillaume Chatelet (gchatelet)

<details>
<summary>Changes</summary>

The [standard](https://eel.is/c++draft/expr.add#<!-- -->4.3) forbids forming pointers to invalid objects even if the pointer is never read from or written to. This patch makes sure that we don't do pointer arithmetic on invalid pointers.


---
Full diff: https://github.com/llvm/llvm-project/pull/74295.diff


1 Files Affected:

- (modified) libc/src/string/memory_utils/utils.h (+3-3) 


``````````diff
diff --git a/libc/src/string/memory_utils/utils.h b/libc/src/string/memory_utils/utils.h
index f70880ee853d3..9c293185a2e9f 100644
--- a/libc/src/string/memory_utils/utils.h
+++ b/libc/src/string/memory_utils/utils.h
@@ -341,9 +341,9 @@ void align_p1_to_next_boundary(T1 *__restrict &p1, T2 *__restrict &p2,
 }
 
 // Same as align_p1_to_next_boundary above but with a single pointer instead.
-template <size_t SIZE, typename T1>
-LIBC_INLINE void align_to_next_boundary(T1 *&p1, size_t &count) {
-  CPtr dummy;
+template <size_t SIZE, typename T>
+LIBC_INLINE void align_to_next_boundary(T *&p1, size_t &count) {
+  const T *dummy = p1;
   align_p1_to_next_boundary<SIZE>(p1, dummy, count);
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/74295