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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 4 Sep 2020 11:42:42 -0700
Message-ID: <CAHk-=wjUUBnp9JSK+u8gYQ-RpMZxgd3UfvpihCPA_vSN_8G8Mg@mail.gmail.com>
Subject: Re: remove the last set_fs() in common code, and remove it for x86
 and powerpc v3
To:     Alexey Dobriyan <adobriyan@gmail.com>
Cc:     Ingo Molnar <mingo@kernel.org>, Christoph Hellwig <hch@lst.de>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Michael Ellerman <mpe@ellerman.id.au>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
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On Fri, Sep 4, 2020 at 10:58 AM Alexey Dobriyan <adobriyan@gmail.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