Messages in this thread | | | Date | Fri, 17 Jul 2015 10:39:48 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC][PATCH] x86, fpu: dynamically allocate 'struct fpu' |
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* Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Jul 16, 2015 at 12:14:37PM -0700, Dave Hansen wrote: > > +++ b/arch/x86/kernel/fpu/init.c 2015-07-16 12:02:15.284280976 -0700 > > @@ -136,6 +136,45 @@ static void __init fpu__init_system_gene > > unsigned int xstate_size; > > EXPORT_SYMBOL_GPL(xstate_size); > > > > +#define CHECK_MEMBER_AT_END_OF(TYPE, MEMBER) \ > > + BUILD_BUG_ON((sizeof(TYPE) - \ > > + offsetof(TYPE, MEMBER) - \ > > + sizeof(((TYPE *)0)->MEMBER)) > \ > > + 0) \ > > + > > +/* > > + * We append the 'struct fpu' to the task_struct. > > + */ > > +int __weak arch_task_struct_size(void) > > +{ > > + int task_size = sizeof(struct task_struct); > > + > > + /* > > + * Subtract off the static size of the register state. > > + * It potentially has a bunch of padding. > > + */ > > + task_size -= sizeof(((struct task_struct *)0)->thread.fpu.state); > > + > > + /* > > + * Add back the dynamically-calculated register state > > + * size. > > + */ > > + task_size += xstate_size; > > + > > + /* > > + * We dynamically size 'struct fpu', so we require that > > + * it be at the end of 'thread_struct' and that > > + * 'thread_struct' be at the end of 'task_struct'. If > > + * you hit a compile error here, check the structure to > > + * see if something got added to the end. > > + */ > > + CHECK_MEMBER_AT_END_OF(struct fpu, state); > > + CHECK_MEMBER_AT_END_OF(struct thread_struct, fpu); > > + CHECK_MEMBER_AT_END_OF(struct task_struct, thread); > > + > > + return task_size; > > +} > > Since you want these invariants true at all times, maybe put the > BUILD_BUG_ON() in generic code instead of x86 specific? That way people > poking at other archs are less likely to accidentally break your stuff.
Yeah.
Thanks,
Ingo
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