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

Vineet Gupta
2016-10-17T22:38:19Z

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
>