Re: Help on memchr() EGLIBC assembly code

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Jul 13, 2009 at 07:16:16PM -0300, Matt Turner wrote:
> On Mon, Jul 13, 2009 at 6:17 PM, Aurelien Jarno<aurelien@aurel32.net> wrote:
> > On Mon, Jul 13, 2009 at 02:24:00PM -0400, Carlos O'Donell wrote:
> >> On Mon, Jul 13, 2009 at 1:31 PM, Aurelien Jarno<aurelien@aurel32.net> wrote:
> >> > With a lot of patches (E)GLIBC 2.10 builds on alpha, but it fails on the
> >> > testsuite for the memchr() function, which is an optimized assembly code
> >> > on alpha. Unfortunately I don't speak alpha assembly very well, so help
> >> > is needed.
> >> >
> >> > The problem is that the memchr() function on alpha uses prefetch, which
> >> > can cause a page boundary to be crossed, while the standards (POSIX and
> >> > C99) says it should stop when a match is found.
> >> >
> >> > I have built a small testcase (see file attached), which contains the
> >> > code to trigger the bug and the assembly code of the memchr() function,
> >> > copied from EGLIBC.
> >> >
> >> > It would be nice if someone can fix the assembly code so that the
> >> > prefetching does not create memory faults. Thanks in advance.
> >>
> >> If you remove:
> >> ./sysdeps/alpha/alphaev6/memchr.S
> >> ./sysdeps/alpha/memchr.S
> >> and allow the build to fallback on string/memchr.c do the tests pass?
> >>
> >> You can always add memchr.S routines back in a later release if you
> >> need an immediate workaround.
> >
> > Yeah, it works, and that's actually my plan if I get no answer. But I
> > would really like to see this fixed now, as otherwise, it will most
> > probably stay like that indefinitely.
> >
> > --
> > Aurelien Jarno                          GPG: 1024D/F1BCDB73
> > aurelien@aurel32.net                 http://www.aurel32.net
> >
> 
> I'm copying Richard Henderson and Ivan Kokshayshy on this, as they are
> without a doubt the most knowledgeable people about this sort of
> thing.

Thanks.

> As an aside, please make sure these two bugs are fixed in eglibc (I
> don't know if they exist in eglibc, but I do realize that you filed
> them against glibc yourself -- so this is just a reminder).
> 
> http://sources.redhat.com/bugzilla/show_bug.cgi?id=5350
> http://sources.redhat.com/bugzilla/show_bug.cgi?id=5400
> 

I have already put a first set of patches needed for alpha in a git
repository [1], and sent a pull request on the libc-ports mailing list.
I hope it will work better than filling bug reports. If it also fails,
I'll send them to EGLIBC.

[1]
http://git.aurel32.net/?p=glibc-ports.git;a=shortlog;h=refs/heads/alpha-for-upstream

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net


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