From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Matthias Kaehlcke <mka@chromium.org>
Cc: Chris J Arges <chris.j.arges@canonical.com>,
Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Douglas Anderson <dianders@chromium.org>,
Michael Davidson <md@google.com>,
Greg Hackmann <ghackmann@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Stephen Hines <srhines@google.com>,
Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
Bernhard.Rosenkranzer@linaro.org
Subject: Re: [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm"
Date: Wed, 12 Jul 2017 17:36:30 -0500 [thread overview]
Message-ID: <20170712223630.gb237t4vhrqeu5zd@treble> (raw)
In-Reply-To: <20170712223547.fyra43dizqooosbs@treble>
On Wed, Jul 12, 2017 at 05:35:47PM -0500, Josh Poimboeuf wrote:
> On Wed, Jul 12, 2017 at 03:20:40PM -0700, Matthias Kaehlcke wrote:
> > > This is admittedly an awkward way of achieving this goal, but it's the
> > > only way I know how to do it with GCC.
> > >
> > > What extra instruction does clang add?
> >
> > I was looking at the get_user() call in drm_mode_setcrtc(). The code
> > generated by clang without the patch is:
> >
> > if (get_user(out_id, &set_connectors_ptr[i])) {
> > ffffffff81386955: 4a 8d 04 bd 00 00 00 lea 0x0(,%r15,4),%rax
> > ffffffff8138695c: 00
> > ffffffff8138695d: 49 03 06 add (%r14),%rax
> > ffffffff81386960: e8 2b a5 f0 ff callq ffffffff81290e90 <__get_user_4>
> >
> > And with the patch:
> >
> > if (get_user(out_id, &set_connectors_ptr[i])) {
> > ffffffff81386a56: 4a 8d 04 bd 00 00 00 lea 0x0(,%r15,4),%rax
> > ffffffff81386a5d: 00
> > ffffffff81386a5e: 49 03 06 add (%r14),%rax
> > ffffffff81386a61: 48 8b 64 24 28 mov 0x28(%rsp),%rsp
> > ffffffff81386a66: e8 15 a5 f0 ff callq
> > ffffffff81290f80 <__get_user_4>
>
> Hm, that seems odd. Can you sure the disassembly for the whole
> function?
Er, share :-)
--
Josh
next prev parent reply other threads:[~2017-07-12 22:36 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-12 21:27 [PATCH] Revert "x86/uaccess: Add stack frame output operand in get_user() inline asm" Matthias Kaehlcke
2017-07-12 22:12 ` Josh Poimboeuf
2017-07-12 22:20 ` Matthias Kaehlcke
2017-07-12 22:35 ` Josh Poimboeuf
2017-07-12 22:36 ` Josh Poimboeuf [this message]
2017-07-12 23:22 ` Matthias Kaehlcke
2017-07-13 18:00 ` Josh Poimboeuf
2017-07-13 18:47 ` Matthias Kaehlcke
2017-07-13 19:25 ` Josh Poimboeuf
2017-07-13 19:38 ` Michael Davidson
2017-07-13 20:18 ` Josh Poimboeuf
2017-07-13 20:20 ` Andrey Rybainin
2017-07-13 20:34 ` Josh Poimboeuf
2017-07-13 21:12 ` Matthias Kaehlcke
2017-07-13 21:34 ` Josh Poimboeuf
2017-07-13 21:57 ` Matthias Kaehlcke
2017-07-19 17:46 ` Josh Poimboeuf
2017-07-19 21:50 ` Matthias Kaehlcke
2017-07-20 10:01 ` Andrey Ryabinin
2017-07-20 15:18 ` Josh Poimboeuf
2017-07-20 15:30 ` Andrey Ryabinin
2017-07-20 20:56 ` Josh Poimboeuf
2017-07-21 9:13 ` Andrey Ryabinin
2017-07-21 13:24 ` Josh Poimboeuf
2017-07-29 0:38 ` Matthias Kaehlcke
2017-07-29 0:55 ` Josh Poimboeuf
2017-07-29 0:58 ` Josh Poimboeuf
2017-07-29 1:06 ` Matthias Kaehlcke
2017-07-13 21:14 ` Matthias Kaehlcke
2017-07-13 21:25 ` Andrey Rybainin
2017-07-13 21:43 ` Matthias Kaehlcke
2017-07-13 21:52 ` Josh Poimboeuf
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