Re: [PATCH v3 04/22] x86/doublefault: Make memmove() notrace/NOKPROBE

Peter Zijlstra
2020-02-19T15:41:02Z

On Wed, Feb 19, 2020 at 10:36:14AM -0500, Steven Rostedt wrote:
> On Wed, 19 Feb 2020 15:47:28 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > --- a/arch/x86/lib/memcpy_32.c
> > +++ b/arch/x86/lib/memcpy_32.c
> > @@ -21,7 +21,7 @@ __visible void *memset(void *s, int c, s
> > }
> > EXPORT_SYMBOL(memset);
> >
> > -__visible void *memmove(void *dest, const void *src, size_t n)
> > +__visible notrace void *memmove(void *dest, const void *src, size_t n)
> > {
> > int d0,d1,d2,d3,d4,d5;
> > char *ret = dest;
> > @@ -207,3 +207,8 @@ __visible void *memmove(void *dest, cons
> >
> > }
> > EXPORT_SYMBOL(memmove);
>
> Hmm, for things like this, which is adding notrace because of a single
> instance of it (although it is fine to trace in any other instance), it
> would be nice to have a gcc helper that could call "memmove+5" which
> would skip the tracing portion.

Or just open-code the memmove() in do_double_fault() I suppose. I don't
think we care about super optimized code there. It's the bloody ESPFIX
trainwreck.