Commit 25ec02f2 authored Dec 21, 2015 by Jiri Olsa Committed by Ingo Molnar Jan 06, 2016

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 <jolsa@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1450707930-3445-1-git-send-email-jolsa@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 7d92de3a

arch/x86/kernel/fpu/init.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -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: