linux-kernel - Re: [PATCH 3/4] x86: open-code register save/restore in trace

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Message-ID: <CAK1hOcMU0kV1M8dk-iOnTJuY3xtE+tmqqgzTxXnzzuDR2EOuLg@mail.gmail.com>
Date:	Sun, 11 Jan 2015 04:33:58 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	X86 ML <x86@...nel.org>, Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH 3/4] x86: open-code register save/restore in
 trace_hardirqs thunks

On Sat, Jan 10, 2015 at 11:41 PM, Borislav Petkov <bp@...en8.de> wrote:
> On Sat, Jan 10, 2015 at 11:35:58PM +0100, Denys Vlasenko wrote:
>> I don't know either... it seems to be used after push_cfi
>> *sometimes*, not always:
>>
>> .macro op_safe_regs op
>> ENTRY(\op\()_safe_regs)
>>         CFI_STARTPROC
>>         pushl_cfi %ebx
>>         pushl_cfi %ebp
>>         pushl_cfi %esi
>>         pushl_cfi %edi
>>
>> but
>>
>> ENTRY(csum_partial)
>>         CFI_STARTPROC
>>         pushl_cfi %esi
>>         CFI_REL_OFFSET esi, 0
>>         pushl_cfi %ebx
>>         CFI_REL_OFFSET ebx, 0
>>
>> We need an expert to enlighten us.
>
> I think Andy had it:
>
> https://lkml.kernel.org/r/CALCETrUuJ8T%2BLp23uYezHvxAtF-L_20dOaD4aDxciE7xZqDK3w@mail.gmail.com
>
> So we better hide that crap in the macro at least, like the rest of the
> CFI gunk.

I understand Andy's post.
My question is, what about places like this?

> .macro op_safe_regs op
> ENTRY(\op\()_safe_regs)
>         CFI_STARTPROC
>         pushl_cfi %ebx
>         pushl_cfi %ebp
>         pushl_cfi %esi
>         pushl_cfi %edi

Do we need to convert it to use macros which also do
"CFI_REL_OFFSET reg, 0" thingy, or not?
In either case: why?
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