[libc-commits] [libc] Create a poor-developer's msan for libc wide read functions. (PR #170586)

[via libc-commits]

https://github.com/Sterling-Augustine created https://github.com/llvm/llvm-project/pull/170586

Most libcs optimize functions like strlen by reading in chunks larger than a single character. As part of "the implementation", they can legally do this as long as they are careful not to read invalid memory.

However, such tricks prevents those functions from being tested under the various sanitizers.

This PR creates a test framework that can report when one of these functions read or write in an invalid way without using the sanitizers.

>From 33b3c44babbb8c888864f1be6b824b624d3370f4 Mon Sep 17 00:00:00 2001
From: Sterling Augustine <saugustine at google.com>
Date: Wed, 3 Dec 2025 16:33:47 -0800
Subject: [PATCH] Create a poor-developer's msan for libc wide read functions.

Most libcs optimize functions like strlen by reading in chunks larger
than a single character. As part of "the implementation", they can
legally do this as long as they are careful not to read invalid
memory.

However, such tricks prevents those functions from being tested under
the various sanitizers.

This PR creates a test framework that can report when one of these
functions read or write in an invalid way without using the
sanitizers.
---
 libc/test/src/strings/CMakeLists.txt | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/libc/test/src/strings/CMakeLists.txt b/libc/test/src/strings/CMakeLists.txt
index 5f70dc024f6ce..0ccd0dc302943 100644
--- a/libc/test/src/strings/CMakeLists.txt
+++ b/libc/test/src/strings/CMakeLists.txt
@@ -110,5 +110,15 @@ add_libc_test(
     libc.src.strings.strncasecmp_l
 )
 
+add_libc_test(
+  wide_read_memory_test
+  SUITE
+    libc-strings-tests
+  SRCS
+    wide_read_memory_test.cpp
+  DEPENDS
+    libc.src.string.strlen
+)
+
 add_libc_multi_impl_test(bcmp libc-strings-tests SRCS bcmp_test.cpp)
 add_libc_multi_impl_test(bzero libc-strings-tests SRCS bzero_test.cpp)