linux-kernel - Re: remove the last set_fs() in common code, and remove it for x86 and powerpc v3

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Date:   Fri, 4 Sep 2020 11:42:42 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: remove the last set_fs() in common code, and remove it for x86
 and powerpc v3

On Fri, Sep 4, 2020 at 10:58 AM Alexey Dobriyan <adobriyan@...il.com> wrote:
>
> set_fs() is older than some kernel hackers!
>
>         $ cd linux-0.11/
>         $ find . -type f -name '*.h' | xargs grep -e set_fs -w -n -A3

Oh, it's older than that. It was there (as set_fs) in 0.10, and may
even predate that. But sadly, I don't have tar-balls for 0.02 and
0.03, so can't check.

The actual use of %fs as the user space segment is already there in
0.01, but there was no 'set_fs()'. That was a simpler and more direct
time, and "get_fs()" looked like this back then:

  #define _fs() ({ \
  register unsigned short __res; \
  __asm__("mov %%fs,%%ax":"=a" (__res):); \
  __res;})

and all the setting was basically part of the kernel entry asm and. Lovely.

                 Linus