linux-kernel - Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put

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Date:   Sat, 13 Jun 2020 20:47:11 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Michael Ellerman <patch-notifications@...erman.id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Paul Mackerras <paulus@...ba.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH v4 1/2] powerpc/uaccess: Implement unsafe_put_user() using 'asm goto'

Nick Desaulniers <ndesaulniers@...gle.com> writes:

> On Thu, Jun 11, 2020 at 4:53 PM Segher Boessenkool
> <segher@...nel.crashing.org> wrote:
>>
>> On Thu, Jun 11, 2020 at 03:43:55PM -0700, Nick Desaulniers wrote:
>> > Segher, Cristophe, I suspect Clang is missing support for the %L and %U
>> > output templates [1].
...
>
> IIUC the bug report correctly, it looks like LLVM is failing for the
> __put_user_asm2_goto case for -m32.  A simple reproducer:
> https://godbolt.org/z/jBBF9b

If you add `-mregnames` you get register names:

https://godbolt.org/z/MxLjhF

foo:
        stw %r3, 0(%r5)
        stw %r4, 4(%r5)
        blr


cheers