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From: YiFei Zhu <zhuyifei1999@gmail.com>
Date: Tue, 20 Apr 2021 01:20:52 -0500
Message-ID: <CABqSeATFW7F3cJkm6t3h1yzJite8yCCbvAQZbafHk=+VbfHntQ@mail.gmail.com>
Subject: Re: [PATCH v2] um: Fix stack pointer alignment
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To: Johannes Berg <johannes@sipsolutions.net>, Colin Ian King <colin.king@canonical.com>
Cc: linux-um@lists.infradead.org, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, Anton Ivanov <anton.ivanov@cambridgegreys.com>, Benjamin Berg <benjamin@sipsolutions.net>

On Tue, Apr 20, 2021 at 12:47 AM YiFei Zhu <zhuyifei1999@gmail.com> wrote:
>   movaps (%rdx),%xmm0
>   movaps %xmm0,(%r12)
>
> The move from xmm0 to stack is omitted.

I looked into this a bit further and thought I should clarify, these
two instructions belong to `current_poll = next_poll`. AFAICT, `tmp =
current_poll` is compiled to:

  movabs $0x605198b0,%r12 ; <current_poll>
  [...]
  movabs 0x605198b8,%rax ; <current_poll+8>
  mov    (%r12),%rcx

and `next_poll = tmp` is:

  movabs %rax,0x605198a8 ; <next_poll+8>
  mov    %rcx,(%rdx)

So it uses two registers, rax and rcx to store tmp, rather than on the stack.

YiFei Zhu

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