From: Geert Uytterhoeven <geert@linux-m68k.org>
To: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Linux-sh list <linux-sh@vger.kernel.org>,
Rich Felker <dalias@libc.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sh: Implement __get_user_u64() required for 64-bit get_user()
Date: Sun, 31 May 2020 10:43:11 +0000 [thread overview]
Message-ID: <CAMuHMdXzje-qFH=pGoouSuXTZYf4NvnzbaYxTm_boMek-DbWMg@mail.gmail.com> (raw)
In-Reply-To: <2ad089c1-75cf-0986-c40f-c7f3f8fd6ead@physik.fu-berlin.de>
Hi Adrian,
On Sun, May 31, 2020 at 11:59 AM John Paul Adrian Glaubitz
<glaubitz@physik.fu-berlin.de> wrote:
> On 5/31/20 11:54 AM, John Paul Adrian Glaubitz wrote:
> > On 5/31/20 11:52 AM, Geert Uytterhoeven wrote:
> >> As this is the 64-bit variant, I think this single move should be
> >> replaced by a double move:
> >>
> >> "mov #0,%R1\n\t" \
> >> "mov #0,%S1\n\t" \
> >>
> >> Same for the big endian version below.
> >>
> >> Disclaimer: uncompiled, untested, no SH assembler expert.
> >
> > Right, this makes sense. I'll send a new patch shortly.
>
> Hmm, this change is not the case for __put_user_asm() vs. __put_user_u64().
> But I have to admit, I don't know what the part below "3:\n\t" is for.
It's part of the exception handling, in case the passed (userspace) pointer
points to an inaccessible address, and triggers an exception.
For an invalid store, nothing is done, besides returning -EFAULT.
Hence there's no "mov #0, %1\n\t" in the put_user case.
For an invalid load, the data is replaced by zero, and -EFAULT is returned.
> +__asm__ __volatile__( \
> + "1:\n\t" \
> + "mov.l %2,%R1\n\t" \
> + "mov.l %T2,%S1\n\t" \
> + "2:\n" \
(reordering the two sections for easier explanation)
> + ".section __ex_table,\"a\"\n\t" \
> + ".long 1b, 3b\n\t" \
In case an exception happens for the instruction at 1b, jump to 3b.
Note that the m68k version has two entries here: one for each half of
the 64-bit access[*].
I don't know if that is really needed (and thus SH needs it, too), or if
the exception code handles subsequent instructions automatically.
> + ".section .fixup,\"ax\"\n" \
> + "3:\n\t" \
> + "mov #0, %1\n\t" \
Return zero instead of the data at the (invalid) address.
> + "mov.l 4f, %0\n\t" \
> + "jmp @%0\n\t" \
Resume at 2b.
Remember: branch delay slot, so the instruction below is executed first!
> + " mov %3, %0\n\t" \
Set err to -EFAULT.
> + ".balign 4\n" \
> + "4: .long 2b\n\t" \
> + ".previous\n" \
> + ".previous" \
> + :"=&r" (err), "=&r" (x) \
> + :"m" (__m(addr)), "i" (-EFAULT), "0" (err)); })
[*] arch/m68k/include/asm/uaccess_mm.h
"1: "MOVES".l (%2)+,%1\n" \
"2: "MOVES".l (%2),%R1\n" \
" .section __ex_table,\"a\"\n" \
" .align 4\n" \
" .long 1b,10b\n" \
" .long 2b,10b\n" \
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2020-05-31 10:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-29 17:45 [RESEND] sh: Implement __get_user_u64() required for 64-bit get_user() John Paul Adrian Glaubitz
2020-05-29 17:45 ` [PATCH] " John Paul Adrian Glaubitz
2020-05-31 9:52 ` Geert Uytterhoeven
2020-05-31 9:54 ` John Paul Adrian Glaubitz
2020-05-31 9:59 ` John Paul Adrian Glaubitz
2020-05-31 10:43 ` Geert Uytterhoeven [this message]
2020-05-31 10:52 ` John Paul Adrian Glaubitz
2020-06-01 3:03 ` Rich Felker
2020-06-01 9:02 ` Geert Uytterhoeven
2020-06-01 9:13 ` John Paul Adrian Glaubitz
2020-06-01 16:57 ` Rich Felker
2020-06-01 20:26 ` Michael Karcher
2020-06-01 20:50 ` Rich Felker
2020-06-02 10:19 ` Michael Karcher
-- strict thread matches above, loose matches on Subject: below --
2020-06-11 7:58 [PATCH v3] " John Paul Adrian Glaubitz
2020-06-11 7:58 ` [PATCH] " John Paul Adrian Glaubitz
2020-06-27 15:26 ` Yoshinori Sato
2020-05-29 17:34 John Paul Adrian Glaubitz
2020-05-29 17:34 ` [PATCH] sh: Implement __get_user_u64() required for 64-bit get_user() John Paul Adrian Glaubitz
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