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[ndesaulniers at google.com]

Date: Thu, 11 Jun 2020 15:38:38 -0700
From: Nick Desaulniers <ndesaulniers at google.com>
To: Michael Ellerman <patch-notifications at ellerman.id.au>,
	christophe.leroy at c-s.fr, segher at kernel.crashing.org
Cc: Christophe Leroy <christophe.leroy at c-s.fr>,
	Benjamin Herrenschmidt <benh at kernel.crashing.org>,
	Paul Mackerras <paulus at samba.org>, npiggin at gmail.com,
	segher at kernel.crashing.org, linuxppc-dev at lists.ozlabs.org,
	linux-kernel at vger.kernel.org, clang-built-linux at googlegroups.com
Subject: Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user()
  using 'asm goto'
Message-ID: <20200611223838.GA60089 at google.com>
References:  
<23e680624680a9a5405f4b88740d2596d4b17c26.1587143308.git.christophe.leroy at c-s.fr>
  <49YBKY13Szz9sT4 at ozlabs.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <49YBKY13Szz9sT4 at ozlabs.org>

On Fri, May 29, 2020 at 02:24:16PM +1000, Michael Ellerman wrote:
> On Fri, 2020-04-17 at 17:08:51 UTC, Christophe Leroy wrote:
> > unsafe_put_user() is designed to take benefit of 'asm goto'.
> >
> > Instead of using the standard __put_user() approach and branch
> > based on the returned error, use 'asm goto' and make the
> > exception code branch directly to the error label. There is
> > no code anymore in the fixup section.
> >
> > This change significantly simplifies functions using
> > unsafe_put_user()
> ...
> >
> > Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> > Reviewed-by: Segher Boessenkool <segher at kernel.crashing.org>

> Applied to powerpc topic/uaccess-ppc, thanks.

> https://git.kernel.org/powerpc/c/334710b1496af8a0960e70121f850e209c20958f

> cheers

Hello!  It seems this patch broke our ppc32 builds, and we had to
disable them [0]. :(

 From what I can tell, though Michael mentioned this was merged on May
29, but our CI of -next was green for ppc32 until June 4, then mainline
went red June 6.  So this patch only got 2 days of soak time before the
merge window opened.

A general issue with the -next workflow seems to be that patches get
different amounts of soak time.  For higher risk patches like this one,
can I please ask that they be help back a release if close to the merge
window?

Segher, Cristophe, I suspect Clang is missing support for the %L and %U
output templates [1]. I've implemented support for some of these before
in Clang via the documentation at [2], but these seem to be machine
specific? Can you please point me to documentation/unit tests/source for
these so that I can figure out what they should be doing, and look into
implementing them in Clang?

(Apologies for the tone off this email; I had typed up a nice fuller
report with links, but it seemed that mutt wrote out an empty postponed
file, and I kind of just want to put my laptop in the garbage right now.
I suspect our internal SMTP tool will also mess up some headers, but
lets see (Also, too lazy+angry right now to solve).)

[0] https://github.com/ClangBuiltLinux/continuous-integration/pull/279
[1] https://bugs.llvm.org/show_bug.cgi?id=46186
[2]  
https://gcc.gnu.org/onlinedocs/gccint/Output-Template.html#Output-Template