Re: [PATCH -tip v3 1/2] kcov: Make runtime functions noinstr-compatible

Peter Zijlstra
2020-06-17T15:55:41Z

On Wed, Jun 17, 2020 at 05:19:59PM +0200, Marco Elver wrote:

> > Does GCC (8, as per the new KASAN thing) have that
> > __builtin_memcpy_inline() ?
>
> No, sadly it doesn't. Only Clang 11. :-/
>
> But using a call to __memcpy() somehow breaks with Clang+KCSAN. Yet,
> it's not the memcpy that BUGs, but once again check_preemption_disabled
> (which is noinstr!). Just adding calls anywhere here seems to results in
> unpredictable behaviour. Are we running out of stack space?

Very likely, bad_iret is running on that entry_stack you found, and as
you found, it is puny.

Andy wanted to make it a full page a while ago, so I suppose the
question is do we do that now?