linux-kernel - Re: [RFC PATCH v2] MIPS: Kconfig: Select ARCH_WANT_FRAME

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Message-ID: <ea260945-ced5-3cf0-d1cc-8c92f04aaf92@loongson.cn>
Date:   Tue, 17 Nov 2020 10:17:39 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [RFC PATCH v2] MIPS: Kconfig: Select ARCH_WANT_FRAME_POINTERS

On 11/16/2020 11:14 PM, Thomas Bogendoerfer wrote:
> On Mon, Nov 16, 2020 at 05:55:06PM +0800, Tiezhu Yang wrote:
>> Select ARCH_WANT_FRAME_POINTERS to fix the following build error under
>> CONFIG_DEBUG_ATOMIC_SLEEP:
>>
>>    CC      arch/mips/kernel/signal.o
>> {standard input}: Assembler messages:
>> {standard input}:1775: Error: Unable to parse register name $fp
>> scripts/Makefile.build:283: recipe for target 'arch/mips/kernel/signal.o' failed
>> make[2]: *** [arch/mips/kernel/signal.o] Error 1
>> scripts/Makefile.build:500: recipe for target 'arch/mips/kernel' failed
>> make[1]: *** [arch/mips/kernel] Error 2
>> Makefile:1799: recipe for target 'arch/mips' failed
>> make: *** [arch/mips] Error 2
> I don't see this error and to me it looks strange to fix that with
> enablding frame pointers... What gcc is this ?

I found this build error used with gcc 4.9.4.
I try it used with gcc 7.3.1 and it has no problem.
We can use new gcc version to avoid this build error.

Additionally, I want to know whether ARCH_WANT_FRAME_POINTERS
is necessary for MIPS to get more debugging info, with this
config we can enable the config FRAME_POINTER by default and
disable it manually.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Makefile#n790
ifdef CONFIG_FRAME_POINTER
KBUILD_CFLAGS   += -fno-omit-frame-pointer -fno-optimize-sibling-calls

Thanks,
Tiezhu