linux-kernel - Re: [PATCH] x86: General protection fault after STR (32 bit systems only)

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Message-ID: <CAK1hOcPvst1+vT_3_m0t7HZF_fz9zjDd_azyWj6n0Ma-qY3ZQQ@mail.gmail.com>
Date:	Sat, 13 Jun 2015 00:45:29 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Brian Gerst <brgerst@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, X86 ML <x86@...nel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: General protection fault after STR (32 bit systems only)

On Fri, Jun 12, 2015 at 5:48 PM, Brian Gerst <brgerst@...il.com> wrote:
> If you follow the convoluted flow of the calls in this file,
> ...

Speaking of which. It is indeed quite bad.

For one, saved_eip is only ever set to point to ret_point:

ENTRY(saved_eip)        .long   0
...

        movl    $ret_point, saved_eip

and it has just a single user, where an indirect jump
through it is performed:

        # jump to place where we left off
        movl    saved_eip, %eax
        jmp     *%eax

No comments why it is so.

All this seems to be equivalent to trivial

        # jump to place where we left off
        jmp     ret_point

Am I missing something?
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