netdev - Re: [PATCH v2 20/20] ppc: propagate the calling conventions change down to csum_partial_copy

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Date:   Thu, 15 Oct 2020 00:54:08 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 20/20] ppc: propagate the calling conventions change
 down to csum_partial_copy_generic()

On Thu, Oct 15, 2020 at 12:53 AM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Wed, Oct 14, 2020 at 3:51 PM Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> >
> > I think it's this instruction:
> >
> >         addi    r1,r1,16
> >
> > that should be removed from the function exit, because Al removed the
> >
> > -       stwu    r1,-16(r1)
> >
> > on function entry.
> >
> > So I think you end up with a corrupt stack pointer and basically
> > random behavior.
> >
> > Mind trying that? (This is obviously all in
> > arch/powerpc/lib/checksum_32.S, the csum_partial_copy_generic()
> > function).
>
> Patch attached to make it easier to test.
>
> NOTE! This is ENTIRELY untested. My ppc asm is so rusty that I might
> be barking entirely up the wrong tree, and I just made things much
> worse.

Indeed - exactly the same thing that's in my tree. Writing a commit
message for it now.

Jason