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

[Guillaume Chatelet via libc-commits]

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

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.


>From e00296763973d6a32e4200845c30c29478869622 Mon Sep 17 00:00:00 2001
From: Guillaume Chatelet <gchatelet at google.com>
Date: Mon, 4 Dec 2023 09:43:31 +0000
Subject: [PATCH] [libc] Fix UB in memory utils

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.
---
 libc/src/string/memory_utils/utils.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

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);
 }