linux-kernel - Re: [PREVIEW 10/10] linkage: add .cfi

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Date:   Fri, 17 Feb 2017 14:36:15 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     mingo@...hat.com, tglx@...utronix.de, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PREVIEW 10/10] linkage: add .cfi_{start/end}proc to
 ENTRY/ENDPROC

On 02/17/2017, 02:16 PM, Josh Poimboeuf wrote:
> On Fri, Feb 17, 2017 at 11:47:57AM +0100, Jiri Slaby wrote:
>> This is just a preview, not to merged now, only later with DWARF
>> unwinder series. This is what the series will serve for (aside from
>> cleanup and unification).
>>
>> I am aware of CFI_STARTPROC and CFI_ENDPROC left defined in other archs
>> in spite of cfi annotations removal ages ago. For simplicity. I am using
>> DW_ prefix here.
> 
> If objtool is going to be generating CFI instructions, why not have it
> generate .cfi_startproc and .cfi_endproc too?

I tried that, but in many places it is very hard to recognize start
and/or end of a function. Having .cfi_startproc and .cfi_endproc in
place makes it rather easy, actually reduced to "emit dwarf instructions
for this code between here and there". Plus pre-prepared .eh_frame only
to be extended. (.eh_frame_hdr has to be rehashed of course.)

thanks,
-- 
js
suse labs