The following commit has been merged into the x86/fpu branch of tip:
Commit-ID: 55228db2697c09abddcb9487c3d9fa5854a932cd
Gitweb: https://git.kernel.org/tip/55228db2697c09abddcb9487c3d9fa5854a932cd
Author: YingChi Long <me@xxxxxxxxx>
AuthorDate: Fri, 18 Nov 2022 08:55:35 +08:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 22 Nov 2022 17:13:03 +01:00
x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN
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@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220925153151.2467884-1-me@xxxxxxxxx
---
arch/x86/kernel/fpu/init.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 8946f89..851eb13 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -133,9 +133,6 @@ static void __init fpu__init_system_generic(void)
fpu__init_system_mxcsr();
}
-/* 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'.
*
@@ -143,8 +140,8 @@ static void __init fpu__init_system_generic(void)
* 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:
|