linux-kernel - Re: [PATCH v3 04/29] x86: assembly, use ENDPROC for functions

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Date:   Fri, 19 May 2017 11:17:24 +0200
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,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v3 04/29] x86: assembly, use ENDPROC for functions

On 05/17/2017, 03:23 PM, Jiri Slaby wrote:
>> So the initial CFI state is different between the two types of
>> "functions".  And there are a lot of other differences.  C-type
>> functions have to follow frame pointer conventions, for example.  So
>> your FUNC_START macro (and objtool) would have to somehow figure out a
>> way to make a distinction between the two.  So it would probably work
>> out better if we kept the distinction between C-type functions and other
>> code.
> 
> Ok, that makes a lot of sense.

A quick question:
Do you consider these to be C-type functions?

  ENTRY(function_hook)
        ret
  END(function_hook)

or this?

  ENTRY(native_load_gs_index)
        pushfq
        DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
        SWAPGS
        movl    %edi, %gs
        SWAPGS
        popfq
        ret
  END(native_load_gs_index)

Both are called from C, but they do not setup frame pointer etc.

thanks,
-- 
js
suse labs