linux-kernel - Re: [PATCH 3/3] riscv: fix __user annotation for __copy

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Date:   Tue, 12 Jun 2018 12:38:11 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     luc.vanoostenryck@...il.com
CC:     atish.patra@....com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, albert@...ive.com
Subject:     Re: [PATCH 3/3] riscv: fix __user annotation for __copy_user()

On Tue, 12 Jun 2018 11:19:57 PDT (-0700), luc.vanoostenryck@...il.com wrote:
> On Tue, Jun 12, 2018 at 7:12 PM, Palmer Dabbelt <palmer@...ive.com> wrote:
>> On Mon, 11 Jun 2018 20:00:08 PDT (-0700), luc.vanoostenryck@...il.com wrote:
>>> On Mon, Jun 11, 2018 at 12:01:37PM -0700, Palmer Dabbelt wrote:
>>>>
>>>> OK, I'll try and figure out what's going on.  We've had a handful of
>>>> headaches trying to get things like '.align 2; .align 2' to actually
>>>> produce
>>>> no NOPs for the second alignment directive, which is surprisingly
>>>> complicated due to the aggressive linker relaxation we do.
>>>
>>>
>>> OK. I imagine indeed but note that no linker is involved here so,
>>> if the problem is still present, it must already be in the assembler.
>>
>>
>> Ah, OK -- in that case then it's just not a bug.  In RISC-V land we handle
>> alignment as part of relaxation in the linker, so if you're looking at the
>> output of the assembler then you'll always see a bunch of NOPs for every
>> alignment directive.  If you 'objdump -dr' you should be able to see the
>> relocations that get emitted, there should be a R_RISCV_ALIGN that points to
>> the run of NOPs.
>
> Ah OK. Indeed I see the R_RISCV_ALIGN.
> Thanks for the explanation.

No problem.  There's heaps of info about this in some blog posts I made a while 
ago if you're interested.