From: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
To: Geert Uytterhoeven <geert@linux-m68k.org>
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 10:52:20 +0000 [thread overview]
Message-ID: <f281aec4-b66c-393b-bb2e-93916abd8a34@physik.fu-berlin.de> (raw)
In-Reply-To: <CAMuHMdXzje-qFH=pGoouSuXTZYf4NvnzbaYxTm_boMek-DbWMg@mail.gmail.com>
Hi Geert!
Thanks a lot for the explanation!
On 5/31/20 12:43 PM, Geert Uytterhoeven wrote:
>> 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.
I have replaced it with two individual mov's now as suggested since I now
understand what's happening here.
> 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.
Hmm. I assume this is something one of the SH maintainers or Yutaka Niibe
can answer.
>> + ".section .fixup,\"ax\"\n" \
>> + "3:\n\t" \
>> + "mov #0, %1\n\t" \
>
> Return zero instead of the data at the (invalid) address.
Makes sense.
>> + "mov.l 4f, %0\n\t" \
>> + "jmp @%0\n\t" \
>
> Resume at 2b.
> Remember: branch delay slot, so the instruction below is executed first!
I didn't even know that SH has delay slots.
>> + " mov %3, %0\n\t" \
>
> Set err to -EFAULT.
Yes.
>> + ".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" \
>
Hmm. I'll wait for more feedback whether need to do the same as on m68k here.
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
next prev parent reply other threads:[~2020-05-31 10:52 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
2020-05-31 10:52 ` John Paul Adrian Glaubitz [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f281aec4-b66c-393b-bb2e-93916abd8a34@physik.fu-berlin.de \
--to=glaubitz@physik.fu-berlin.de \
--cc=dalias@libc.org \
--cc=geert@linux-m68k.org \
--cc=kernel@mkarcher.dialup.fu-berlin.de \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-sh@vger.kernel.org \
--cc=ysato@users.sourceforge.jp \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).