[llvm-branch-commits] [libcxx] release/21.x: [libc++] Add checks for misused hardening macros (#150669) (PR #151582)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/151582

>From 3290ca0fdd69b9c14dfca0c31e4b62360d00a3ed Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Thu, 31 Jul 2025 15:17:56 -0400
Subject: [PATCH] [libc++] Add checks for misused hardening macros (#150669)

Libc++ hardening went through several iterations, sometimes within a
single release. However, some folks in the wild have picked up these
macros that were either public at some point or that were used
temporarily on `main`, and unfortunately those are now ignored.

This can lead to some users thinking they enable hardening when in
reality they don't, which is a pretty big deal. This patch simply checks
various old hardening-related macros and ensures that they are not set,
which will catch such misuse.

(cherry picked from commit 955ece4fa53e5309dd38795efd6a357ddf52963b)
---
 libcxx/include/__config | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/libcxx/include/__config b/libcxx/include/__config
index 3f41e044862ec..fd15e07c5ef7b 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -64,9 +64,21 @@
 
 // HARDENING {
 
-// TODO: Remove in LLVM 21. We're making this an error to catch folks who might not have migrated.
-#  ifdef _LIBCPP_ENABLE_ASSERTIONS
-#    error "_LIBCPP_ENABLE_ASSERTIONS has been removed, please use _LIBCPP_HARDENING_MODE instead"
+// TODO(LLVM 23): Remove this. We're making these an error to catch folks who might not have migrated.
+//       Since hardening went through several changes (many of which impacted user-facing macros),
+//       we're keeping these checks around for a bit longer than usual. Failure to properly configure
+//       hardening results in checks being dropped silently, which is a pretty big deal.
+#  if defined(_LIBCPP_ENABLE_ASSERTIONS)
+#    error "_LIBCPP_ENABLE_ASSERTIONS has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
+#  endif
+#  if defined(_LIBCPP_ENABLE_HARDENED_MODE)
+#    error "_LIBCPP_ENABLE_HARDENED_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
+#  endif
+#  if defined(_LIBCPP_ENABLE_SAFE_MODE)
+#    error "_LIBCPP_ENABLE_SAFE_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
+#  endif
+#  if defined(_LIBCPP_ENABLE_DEBUG_MODE)
+#    error "_LIBCPP_ENABLE_DEBUG_MODE has been removed, please use _LIBCPP_HARDENING_MODE=<mode> instead (see docs)"
 #  endif
 
 // The library provides the macro `_LIBCPP_HARDENING_MODE` which can be set to one of the following values: