Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3)

2017-06-26 Thread Michael Ellerman
Al Viro writes: > On Sun, Jun 25, 2017 at 04:44:09PM -0500, Segher Boessenkool wrote: > >> Do you have a short stand-alone testcase? 4.6 is ancient, of course, but >> the actual problem may still exist in more recent compilers (if it _is_ >> a compiler problem; if it's not, you *really* want to

Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3)

2017-06-25 Thread Al Viro
On Sun, Jun 25, 2017 at 04:44:09PM -0500, Segher Boessenkool wrote: > Do you have a short stand-alone testcase? 4.6 is ancient, of course, but > the actual problem may still exist in more recent compilers (if it _is_ > a compiler problem; if it's not, you *really* want to know :-) ) Enjoy. At l

Re: gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3)

2017-06-25 Thread Segher Boessenkool
On Sun, Jun 25, 2017 at 09:53:24PM +0100, Al Viro wrote: > Confirmed. It manages to bugger the loop immediately after the (successful) > copying of iovec array in rw_copy_check_uvector(); both with and without > INLINE_COPY_FROM_USER it has (just before the call of copy_from_user()) r27 > set to n

gcc 4.6.3 miscompile on ppc32 (was Re: Regression in kernel 4.12-rc1 for Powerpc 32 - bisected to commit 3448890c32c3)

2017-06-25 Thread Al Viro
On Sun, Jun 25, 2017 at 12:14:04PM +0100, Al Viro wrote: > On Sun, Jun 25, 2017 at 10:53:58AM +0100, Al Viro wrote: > > On Sat, Jun 24, 2017 at 12:29:23PM -0500, Larry Finger wrote: > > > > > I made a break through. If I turn off inline copy to/from users for 32-bit > > > ppc with the following pa