[PATCH] x86/fpu: use __alignof__ to avoid UB in TYPE_ALIGN

From: YingChi Long <me@inclyc.cn>
To: tglx@linutronix.de
Cc: me@inclyc.cn, ndesaulniers@google.com,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"Chang S. Bae" <chang.seok.bae@intel.com>,
	linux-kernel@vger.kernel.org
Subject: [PATCH] x86/fpu: use __alignof__ to avoid UB in TYPE_ALIGN
Date: Sun, 25 Sep 2022 23:31:50 +0800	[thread overview]
Message-ID: <20220925153151.2467884-1-me@inclyc.cn> (raw)

WG14 N2350 made very clear that it is an UB having type definitions with
in "offsetof". This patch change the implementation of macro
"TYPE_ALIGN" to builtin "__alignof__" to avoid undefined behavior.

I've grepped all source files to find any type definitions within
"offsetof".

    offsetof\(struct .*\{ .*,

This implementation of macro "TYPE_ALIGN" seemes to be the only case of
type definitions within offsetof in the kernel codebase.

Signed-off-by: YingChi Long <me@inclyc.cn>
Link: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
---
 arch/x86/kernel/fpu/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 621f4b6cac4a..41425ba0b6b1 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -134,7 +134,7 @@ static void __init fpu__init_system_generic(void)
 }
 
 /* Get alignment of the TYPE. */
-#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
+#define TYPE_ALIGN(TYPE) __alignof__(TYPE)
 
 /*
  * Enforce that 'MEMBER' is the last field of 'TYPE'.
-- 
2.35.1

