linux-kernel - Re: proxy_pda was Re: What was in the x86 merge for .20

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Date:	Mon, 15 Jan 2007 21:41:02 +0100
From:	Paweł Sikora <pluto@...k.net>
To:	linux-kernel@...r.kernel.org
Subject: Re: proxy_pda was Re: What was in the x86 merge for .20

Hi,

I've reviewed the thread and can propose a solution.
Let's see e.g. the dev.s ( from fuse.ko ). Currently with gcc-4.2 we get:

fuse_req_init_context:
        movl    $_proxy_pda+8, %edx     #, tmp62
#APP
        movl %gs:8,%ecx #, ret__
#NO_APP
        movl    344(%ecx), %ecx # <variable>.fsuid, <variable>.fsuid
        movl    %ecx, 60(%eax)  # <variable>.fsuid, <variable>.in.h.uid
#APP
        movl %gs:8,%ecx #, ret__
#NO_APP
        movl    360(%ecx), %ecx # <variable>.fsgid, <variable>.fsgid
        movl    %ecx, 64(%eax)  # <variable>.fsgid, <variable>.in.h.gid
#APP
        movl %gs:8,%edx #, ret__
#NO_APP
        movl    164(%edx), %edx # <variable>.pid, <variable>.pid
        movl    %edx, 68(%eax)  # <variable>.pid, <variable>.in.h.pid
        ret

In this scenario gcc is explictly blocked by -fno-strict-aliasing
and massive %gs:8 reloads are present. If you fix aliasing violations
in kernel then you could use -fstrict-aliasing to get what you want.

fuse_req_init_context:
#APP
        movl %gs:8,%ecx #, ret__
#NO_APP
        movl    344(%ecx), %edx # <variable>.fsuid, <variable>.fsuid
        movl    %edx, 60(%eax)  # <variable>.fsuid, <variable>.in.h.uid
        movl    360(%ecx), %edx # <variable>.fsgid, <variable>.fsgid
        movl    %edx, 64(%eax)  # <variable>.fsgid, <variable>.in.h.gid
        movl    164(%ecx), %edx # <variable>.pid, <variable>.pid
        movl    %edx, 68(%eax)  # <variable>.pid, <variable>.in.h.pid
        ret

BR,
Pawel.
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