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

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Message-ID: <CAK1hOcNgnZcF5fZjSSMr+RQQWLGBSjitErd4gj7JxgTMZPGTzQ@mail.gmail.com>
Date:	Sat, 10 Jan 2015 23:35:58 +0100
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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>, Borislav Petkov <bp@...en8.de>,
	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 11:07 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Sat, Jan 10, 2015 at 2:00 PM, Denys Vlasenko <dvlasenk@...hat.com> wrote:
>> +       pushq_cfi %rdi
>> +       CFI_REL_OFFSET rdi, 0
>> +       pushq_cfi %rsi
>> +       CFI_REL_OFFSET rsi, 0
>> +       pushq_cfi %rdx
>> +       CFI_REL_OFFSET rdx, 0
> ..
> Ugh.
>
> This is too ugly, it needs to die.
>
> Why doesn't pushq_cfi do that CFI_REL_OFFSET thing?

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.
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