From: YingChi Long <me@inclyc.cn>
Date: Fri, 18 Nov 2022 08:55:35 +0800
Subject: x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN
Git-commit: 55228db2697c09abddcb9487c3d9fa5854a932cd
Patch-mainline: v6.2-rc1
References: git-fixes
WG14 N2350 specifies that it is an undefined behavior to have type
definitions within offsetof", see
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
This specification is also part of C23.
Therefore, replace the TYPE_ALIGN macro with the _Alignof builtin to
avoid undefined behavior. (_Alignof itself is C11 and the kernel is
built with -gnu11).
ISO C11 _Alignof is subtly different from the GNU C extension
__alignof__. Latter is the preferred alignment and _Alignof the
minimal alignment. For long long on x86 these are 8 and 4
respectively.
The macro TYPE_ALIGN's behavior matches _Alignof rather than
__alignof__.
[ bp: Massage commit message. ]
Signed-off-by: YingChi Long <me@inclyc.cn>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220925153151.2467884-1-me@inclyc.cn
Acked-by: Nikolay Borisov <nik.borisov@suse.com>
---
arch/x86/kernel/fpu/init.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -138,9 +138,6 @@ static void __init fpu__init_system_gene
unsigned int fpu_kernel_xstate_size;
EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size);
-/* Get alignment of the TYPE. */
-#define TYPE_ALIGN(TYPE) offsetof(struct { char x; TYPE test; }, test)
-
/*
* Enforce that 'MEMBER' is the last field of 'TYPE'.
*
@@ -148,8 +145,8 @@ EXPORT_SYMBOL_GPL(fpu_kernel_xstate_size
* because that's how C aligns structs.
*/
#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \
- BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \
- TYPE_ALIGN(TYPE)))
+ BUILD_BUG_ON(sizeof(TYPE) != \
+ ALIGN(offsetofend(TYPE, MEMBER), _Alignof(TYPE)))
/*
* We append the 'struct fpu' to the task_struct: