[PATCH -tip 05/10] kcsan: Remove 'noinline' from __no_kcsan_or_inline

[Marco Elver]

Some compilers incorrectly inline small __no_kcsan functions, which then
results in instrumenting the accesses. For this reason, the 'noinline'
attribute was added to __no_kcsan_or_inline. All known versions of GCC
are affected by this. Supported version of Clang are unaffected, and
never inlines a no_sanitize function.

However, the attribute 'noinline' in __no_kcsan_or_inline causes
unexpected code generation in functions that are __no_kcsan and call a
__no_kcsan_or_inline function.

In certain situations it is expected that the __no_kcsan_or_inline
function is actually inlined by the __no_kcsan function, and *no* calls
are emitted. By removing the 'noinline' attribute we give the compiler
the ability to inline and generate the expected code in __no_kcsan
functions.

Link: https://lkml.kernel.org/r/CANpmjNNOpJk0tprXKB_deiNAv_UmmORf1-2uajLhnLWQQ1hvoA@xxxxxxxxxxxxxx
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
---
 include/linux/compiler.h | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index e24cc3a2bc3e..17c98b215572 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -276,11 +276,9 @@ do {									\
 #ifdef __SANITIZE_THREAD__
 /*
  * Rely on __SANITIZE_THREAD__ instead of CONFIG_KCSAN, to avoid not inlining in
- * compilation units where instrumentation is disabled. The attribute 'noinline'
- * is required for older compilers, where implicit inlining of very small
- * functions renders __no_sanitize_thread ineffective.
+ * compilation units where instrumentation is disabled.
  */
-# define __no_kcsan_or_inline __no_kcsan noinline notrace __maybe_unused
+# define __no_kcsan_or_inline __no_kcsan notrace __maybe_unused
 # define __no_sanitize_or_inline __no_kcsan_or_inline
 #else
 # define __no_kcsan_or_inline __always_inline
-- 
2.26.2.761.g0e0b3e54be-goog