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x86/fpu: Use _Alignof to avoid undefined behavior in TYPE_ALIGN

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commit 55228db269 upstream.

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
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
YingChi Long 2022-11-18 08:55:35 +08:00 committed by Greg Kroah-Hartman
parent f114717dfa
commit 430443f856
1 changed files with 2 additions and 5 deletions
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7
arch/x86/kernel/fpu/init.c
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@ -138,9 +138,6 @@ static void __init fpu__init_system_generic(void)
unsigned int fpu_kernel_xstate_size __ro_after_init;
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: