From 25ec02f2c14466a4549c5dcc044b628c2cc46fde Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Mon, 21 Dec 2015 15:25:30 +0100 Subject: [PATCH] x86/fpu: Properly align size in CHECK_MEMBER_AT_END_OF() macro The CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) checks whether MEMBER is last member of TYPE by evaluating: offsetof(TYPE::MEMBER) + sizeof(TYPE::MEMBER) == sizeof(TYPE) and ensuring TYPE::MEMBER is the last member of the TYPE. This condition breaks on structs that are padded to be aligned. This patch ensures the TYPE alignment is taken into account. This bug was revealed after adding cacheline alignment into struct sched_entity, which broke task_struct::thread check: CHECK_MEMBER_AT_END_OF(struct task_struct, thread); Signed-off-by: Jiri Olsa Signed-off-by: Peter Zijlstra (Intel) Cc: Dave Hansen Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1450707930-3445-1-git-send-email-jolsa@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/kernel/fpu/init.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c index be39b5fde4b9..8e839e7f5e2f 100644 --- a/arch/x86/kernel/fpu/init.c +++ b/arch/x86/kernel/fpu/init.c @@ -143,9 +143,18 @@ static void __init fpu__init_system_generic(void) unsigned int xstate_size; EXPORT_SYMBOL_GPL(xstate_size); -/* Enforce that 'MEMBER' is the last field of 'TYPE': */ +/* 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'. + * + * Align the computed size with alignment of the TYPE, + * because that's how C aligns structs. + */ #define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \ - BUILD_BUG_ON(sizeof(TYPE) != offsetofend(TYPE, MEMBER)) + BUILD_BUG_ON(sizeof(TYPE) != ALIGN(offsetofend(TYPE, MEMBER), \ + TYPE_ALIGN(TYPE))) /* * We append the 'struct fpu' to the task_struct: -- 2.20.1