linux-kernel - Re: Portable assmbler code

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Message-ID: <526CC0AD.8090208@synopsys.com>
Date:	Sun, 27 Oct 2013 12:58:45 +0530
From:	Vineet Gupta <vineetg76@...il.com>
To:	Chen Gang <gang.chen@...anux.com>
CC:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Joern Rennecke <joern.rennecke@...ecosm.com>,
	James Hogan <james.hogan@...tec.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Takashi Iwai <tiwai@...e.de>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	"jeremy.bennett@...ecosm.com" <jeremy.bennett@...ecosm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Claudiu Zissulescu <Claudiu.Zissulescu@...opsys.com>,
	Francois Bedard <Francois.Bedard@...opsys.com>,
	Sam Ravnborg <sam@...nborg.org>, Joe Perches <joe@...ches.com>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: Portable assmbler code - newline

On 10/26/2013 07:08 PM, Chen Gang wrote:
> On 10/25/2013 01:10 PM, Vineet Gupta wrote:
>> On 10/25/2013 01:11 AM, Geert Uytterhoeven wrote:
>>> On Thu, Oct 24, 2013 at 7:28 PM, Vineet Gupta <vineetg76@...il.com> wrote:
>>>>> +CC linux-arch
>>>>>
>>>>> On 10/24/2013 11:33 AM, Richard Weinberger wrote:
>>>>>>> On Thu, Oct 24, 2013 at 7:31 AM, Chen Gang <gang.chen@...anux.com> wrote:
>>>>>>>>>>> For some architectures, tool chain is not smart enough to recognize the
>>>>>>>>>>> macro with multiple lines (e.g. arc tool chain), and for common ".S"
>>>>>>>>>>> file, this kind of macro is also rarely used.
>>>>>>> Does not "not smart enough" mean than the said toolchain is broken/buggy
>>>>>>> or is the kernel using an unsupported notation?
>>>>>>>
>>>>>
>>>>> IMHO this is not broken - rather the code is not fully portable - given that gas
>>>>> ports of arches have differnet notions of what to treat as comment and what newline.
>>>>>
>>>>> Looking as binutils/gas/config, I can see that avr, cris,...are likely broken in
>>>>> the same way as ARC is.
>>>>>
>>>>> Historically ARC has had ';' as comment char, which Joern relatively recently
>>>>> augmented to have '#' as well. However there's legacy codebase which relies on ';'
>>>>> being a comment and we can't change that fact.
>>>>>
>>>>> So can we introduce an ARCH over-ridable newline annotation in linkage.h and other
>>>>> places after auditing. Since asm/linkage.h preempts linux/linkage.h by way of
>>>>> #include it shd be pretty strightforward.
>>>>>
>>>>> Something like below. I can send the formal patch if people think the approach is OK.
>>> By what are you gonna override __ARCH_NL on ARC?
>>> I'm afraid cpp will still turn it into a single line.
>>>
>>
>> Eh ! My untested patch was broken but not because of what you mentioned.
>>
>> For ARC, the ; negating the newline annotation. So the following works (backquote
>> is new line for ARC)
>>
>> diff --git a/arch/arc/include/asm/linkage.h b/arch/arc/include/asm/linkage.h
>> index 0283e9e44e0d..b3eea2999322 100644
>> --- a/arch/arc/include/asm/linkage.h
>> +++ b/arch/arc/include/asm/linkage.h
>> @@ -9,6 +9,8 @@
>>  #ifndef __ASM_LINKAGE_H
>>  #define __ASM_LINKAGE_H
>>
>> +#define __ARCH_NL      `
>> +
>>  #ifdef __ASSEMBLY__
>>
>>
>> diff --git a/include/linux/linkage.h b/include/linux/linkage.h
>> index d3e8ad23a8e0..969e70ad231a 100644
>> --- a/include/linux/linkage.h
>> +++ b/include/linux/linkage.h
>> @@ -6,6 +6,10 @@
>>  #include <linux/export.h>
>>  #include <asm/linkage.h>
>>
>> +#ifndef __ARCH_NL
>> +#define __ARCH_NL      ;
>> +#endif
>> +
>>  #ifdef __cplusplus
>>  #define CPP_ASMLINKAGE extern "C"
>>  #else
>> @@ -75,7 +79,7 @@
>>
>>  #ifndef ENTRY
>>  #define ENTRY(name) \
>> -  .globl name; \
>> +  .globl name __ARCH_NL \
>>    ALIGN; \
> 
> Do we also need consider about "ALIGN;"?

Right - as I said already, above was not a formal patch but a RFC whether we are
on right track. The proper fix will have to audit all such places.


>>    name:
>>  #endif
>>
> 
> For next-20130927 tree, do we also need consider about WEAK, ENDPROC?

Indeed.


> I am not quite sure about it, but I will try. 

So you volunteer to send out a patch base don __ARCH_NL I proposed above ?


> Now, I am just analyzing
> another issue -- maybe the last issue for allmodconfig under arc, which
> may be related with this patch, the errors are:
> 
>       1   Building modules, stage 2.
>       2   MODPOST 2994 modules
>       3 ERROR: "__st_r13_to_r20" [sound/usb/snd-usbmidi-lib.ko] undefined!

Yes we know about this already. This is to do with libgcc linkage. The fix is non
trivial - I'll get back to you on this. For now disable CONFIG_CC_OPTIMIZE_FOR_SIZE.

-Vineet
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