linux-kernel - Re: [PATCH] x86/asm/entry/64: Clean up entry

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Message-ID: <CALCETrUijLddBLQB6n0bgHw+ZbrUYDHAoPh9YGSqRgrRW6yVfA@mail.gmail.com>
Date:	Mon, 6 Jul 2015 11:39:29 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/asm/entry/64: Clean up entry_64.S

On Mon, Jul 6, 2015 at 11:35 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Jul 6, 2015 at 10:41 AM, Ingo Molnar <mingo@...nel.org> wrote:
>>
>> * Sasha Levin <sasha.levin@...cle.com> wrote:
>>
>>> On 07/06/2015 01:20 PM, Andy Lutomirski wrote:
>>> > On Mon, Jul 6, 2015 at 8:00 AM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>> >> >
>>> >> > --- entry.before.o.cmd  2015-07-06 10:48:32.110189938 -0400
>>> >> > +++ entry.after.o.cmd   2015-07-06 10:48:23.509645442 -0400
>>> >> > @@ -1,5 +1,5 @@
>>> >> >
>>> >> > -entry.before.o:     file format elf64-x86-64
>>> >> > +entry.after.o:     file format elf64-x86-64
>>> >> >
>>> >> >
>>> >> >  Disassembly of section .entry.text:
>>> >> > @@ -3961,8 +3961,8 @@
>>> >> >    3b:  09 02                   or     %eax,(%rdx)
>>> >> >         ...
>>> >> >                         3d: R_X86_64_64 .entry.text
>>> >> > -  45:  03 3a                   add    (%rdx),%edi
>>> >> > -  47:  01 3d 03 d6 00 c8       add    %edi,-0x37ff29fd(%rip)        # ffffffffc800d650 <ignore_sysret+0xffffffffc800b1f0>
>>> >> > +  45:  03 33                   add    (%rbx),%esi
>>> >> > +  47:  01 3d 03 d5 00 c8       add    %edi,-0x37ff2afd(%rip)        # ffffffffc800d550 <ignore_sysret+0xffffffffc800b0f0>
>>> > What exactly are you doing to generate this diff?  This all looks really weird.
>>> >
>>> >> >    4d:  44 91                   rex.R xchg %eax,%ecx
>>> >> >    4f:  93                      xchg   %eax,%ebx
>>> >> >    50:  2f                      (bad)
>>> > For example: what on earth is the asm above?
>>>
>>> objdump...
>>
>> Oh, so I'm using 'objdump -d' to compare - but you probably used 'objdump
>> --disassemble-all', to disassemble .data sections as well?
>>
>
> I can reproduce the difference now.  Give me a few minutes to see if I
> can figure out what's causing it.

It's debug info.  If I strip the two .o files, the results are
identical.  I think the differences are just line numbers.

Why would this matter?  Sasha, can you double-check that this patch
really introduced the problem?

--Andy
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