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Re: [PATCH] x86/raid6: correctly check for assembler capabilities

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  Re: [PATCH] x86/raid6: correctly check for assembler capabilities "H. Peter Anvin" <hpa@zytor.com> - 2015-06-16 21:50 +0200
    Re: [PATCH] x86/raid6: correctly check for assembler capabilities Paul Bolle <pebolle@tiscali.nl> - 2015-06-16 22:00 +0200
      Re: [PATCH] x86/raid6: correctly check for assembler capabilities "H. Peter Anvin" <hpa@zytor.com> - 2015-06-16 22:10 +0200
        Re: [PATCH] x86/raid6: correctly check for assembler capabilities Paul Bolle <pebolle@tiscali.nl> - 2015-06-16 22:40 +0200
          Re: [PATCH] x86/raid6: correctly check for assembler capabilities "H. Peter Anvin" <hpa@zytor.com> - 2015-06-16 22:50 +0200
            Re: [PATCH] x86/raid6: correctly check for assembler capabilities Paul Bolle <pebolle@tiscali.nl> - 2015-06-16 23:00 +0200

#1166346 — Re: [PATCH] x86/raid6: correctly check for assembler capabilities

On 02/03/2015 01:03 PM, Paul Bolle wrote:
> On Wed, 2015-02-04 at 07:50 +1100, NeilBrown wrote:
>> Actually the prefix of this macro is "CONFIG_AS_", not "CONFIG_" :-)
>> CONFIG_AS_ is reserved for assembly magic, and is never used by the the
>> kconfig system.
>>
>> (Well..... I might have made bits of that up, but "git grep 'config AS_'"
>> doesn't find anything).
> 
> That's correct, there are no Kconfig symbols starting with AS_. But
> still, I would like to hear whether there's a reasonable chance I might
> convince other people to adopt my peeve.
> 
> The thinking behind that peeve is, basically, that where people
> encounter a CONFIG_* macro they should only have to check the .config
> file to see how that macro was evaluated in the build that was used.
> 

There is a hope/intent that eventually the config system will be able to
incorporate toolchain dependencies for a bunch of reasons.

	-hpa


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#1166349

On Tue, 2015-06-16 at 12:46 -0700, H. Peter Anvin wrote:
> There is a hope/intent that eventually the config system will be able to
> incorporate toolchain dependencies for a bunch of reasons.

This restarts a four months old thread with a one sentence remark. So
could you please elaborate, because now you've left me and, perhaps, the
other people reading this wondering what "toolchain dependencies"
actually means and what those "bunch of reasons" are.

Thanks,


Paul Bolle

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#1166354

On 06/16/2015 12:56 PM, Paul Bolle wrote:
> On Tue, 2015-06-16 at 12:46 -0700, H. Peter Anvin wrote:
>> There is a hope/intent that eventually the config system will be able to
>> incorporate toolchain dependencies for a bunch of reasons.
> 
> This restarts a four months old thread with a one sentence remark. So
> could you please elaborate, because now you've left me and, perhaps, the
> other people reading this wondering what "toolchain dependencies"
> actually means and what those "bunch of reasons" are.
> 

Sorry, missed the date on this in my inbox for some reason.

So this related to the CONFIG_AS_ symbols for assembly.  We really would
like to do things like actually adding dependencies on assembler or
compiler support into Kconfig proper, rather than having two independent
mechanisms.  That way we could do, for example:

config RAID6_AVX2
	depends on X86 && AS_AVX2


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#1166389

On Tue, 2015-06-16 at 13:05 -0700, H. Peter Anvin wrote:
> So this related to the CONFIG_AS_ symbols for assembly.  We really would
> like to do things like actually adding dependencies on assembler or
> compiler support into Kconfig proper, rather than having two independent
> mechanisms.  That way we could do, for example:
> 
> config RAID6_AVX2
> 	depends on X86 && AS_AVX2

I have no idea what AS_AVX2 means, sorry. So what would it mean if
someone has a .config with
    CONFIG_AS_AVX2=foo

Ie, what would happen if someone using a toolchain for which that would
not be possible tries to build a kernel with that symbol set? That
person's .config would end up containing
    # CONFIG_AS_AVX2 is not set

or similar, right? 


Paul Bolle

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#1166397

On 06/16/2015 01:37 PM, Paul Bolle wrote:
> 
> I have no idea what AS_AVX2 means, sorry. So what would it mean if
> someone has a .config with
>     CONFIG_AS_AVX2=foo
> 
> Ie, what would happen if someone using a toolchain for which that would
> not be possible tries to build a kernel with that symbol set? That
> person's .config would end up containing
>     # CONFIG_AS_AVX2 is not set
> 
> or similar, right? 
> 

Yes, these would be generated, not user input.

	-hpa


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#1166405

On Tue, 2015-06-16 at 13:42 -0700, H. Peter Anvin wrote:
> Yes, these would be generated, not user input.

I think someone (Jiri Kosina?) proposed shelling out to set Kconfig
values. I don't think any patches were ever submitted. But I guess
something along those lines would be needed to adopt the .config to the
toolchain at hand. As long as we don't do anything funny once we've
generated the .config file that might just work.

Yes, I know, the devil hides in the details.

Thanks,


Paul Bolle

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