linux-kernel - Re: Build regressions/improvements in v4.9-rc1

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Date:   Mon, 17 Oct 2016 15:37:58 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Michal Marek <mmarek@...e.cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        arcml <linux-snps-arc@...ts.infradead.org>
Subject: Re: Build regressions/improvements in v4.9-rc1

On 10/17/2016 02:02 PM, Arnd Bergmann wrote:
> On Monday, October 17, 2016 9:59:24 AM CEST Vineet Gupta wrote:
>> +CC Arnd, Michal
>>
>> Hi Geert, Arnd
>>
>> Need some guidance here.
>>
>> On 10/17/2016 12:34 AM, Geert Uytterhoeven wrote:
>>>> 48 error regressions:
>>>>>   + /home/kisskb/slave/src/arch/arc/include/asm/atomic.h: Error: bad instruction `llockd r2,[r0]':  => 476
>>>>>   + /home/kisskb/slave/src/arch/arc/include/asm/atomic.h: Error: bad instruction `llockd r2,[r13]':  => 475
>>
>> [snip...]
>>
>>>>>   + /home/kisskb/slave/src/arch/arc/include/asm/atomic.h: Error: bad instruction `scondd r4,[r8]':  => 516
>>>>>   + /home/kisskb/slave/src/arch/arc/include/asm/atomic.h: Error: bad instruction `scondd r6,[r3]':  => 478
>>> arcv2/axs103_smp_defconfig
>>
>>
>> I'm thinking how to address this correctly.
>>
>> This is due to the older version of compiler.  The fix itself is trivial - add an
>> "call as-instr" construct in Makefile to get -DARC_TOOLS_SUPPORT_LLOCKD
>>
>> However the atomic64 API variant (CONFIG_GENERIC_ATOMIC64 or arch native) which
>> gets included in build comes from Kconfig (ISA supports them or not). How do we
>> tie the Makefile info into the Kconfig.
>>
>> We could trigger a build failure for invalid combinations of GENERIC_ATOMIC64 and
>> ARC_TOOLS_SUPPORT_LLOCKD but that would be less than ideal out of box experience.
>>
>> Or the simpler solution is that kisskb upgrades the ARC GNU compiler 
> 
> Some ideas, none of which are perfect:
> 
> - add an #ifndef ARC_TOOLS_SUPPORT_LLOCKD clause in asm/atomic.h that uses
>   .long with hardcoded opcodes in place of the mnemonics.
> 
> - instead of setting CONFIG_GENERIC_ATOMIC64 from Kconfig, add a file
>   in arch/arc/kernel/ that includes lib/atomic64.c if ARC_TOOLS_SUPPORT_LLOCKD
>   is not set.
> 
> - add "-DCONFIG_GENERIC_ATOMIC64" to cflags-y from arch/arc/Makefile if
>   old binutils are found.

I'm tending towards this one - seems cleanest, however...

@Michael can I bother you to upgrade the tools or is this absolutely must for you.

> 
> I think someone was suggesting in the past that Kconfig could be extended
> to make decisions based on the gcc version, and the same thing could
> be done for binutils. Don't remember who that was though. I think a number
> of awkward hacks in the kernel could be simplified if we had this.
> 
> 	And
>