[libc] Fix UB in memory utils

[gchatelet]

The standard 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.

Co-authored-by: Vitaly Buka vitalybuka@google.com

[llvmbot]

@llvm/pr-subscribers-libc

Author: Guillaume Chatelet (gchatelet)

Changes

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 --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);
 }
 

[legrosbuffle]

LGTM, but please tag the change with the original author.