linux-kernel - Re: [PATCH v5 8/8] LoongArch: Add ORC stack unwinder support

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Message-ID: <c172bf73-1e4e-9d4a-4b82-6aeb0f6f4ff8@loongson.cn>
Date:   Thu, 7 Dec 2023 15:43:04 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Xi Ruoyao <xry111@...111.site>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 8/8] LoongArch: Add ORC stack unwinder support



On 12/03/2023 09:20 PM, Xi Ruoyao wrote:
> On Wed, 2023-11-29 at 21:07 +0800, Tiezhu Yang wrote:
>> +KBUILD_AFLAGS			+= $(call cc-option,-mthin-add-sub) $(call cc-option,-Wa$(comma)-mthin-add-sub)
>> +KBUILD_CFLAGS			+= $(call cc-option,-mthin-add-sub) $(call cc-option,-Wa$(comma)-mthin-add-sub)
>> +
>> +ifdef CONFIG_OBJTOOL
>> +KBUILD_CFLAGS			+= -fno-optimize-sibling-calls -fno-jump-tables -falign-functions=4 -falign-labels=4
>> +endif
>
> I still hate regressing the optimization with a passion.

Yes, I agree in general.

>
> And -falign-labels=4 implies -falign-functions=4 so at least we can
> remove -falign-functions=4.

Thanks.

>
> And in GCC >= 14 the defaults are -falign-labels=16 and -falign-
> functions=32.  These values are determined by benchmarking on LA464 so
> I'd suggest using them (maybe unless CONFIG_CC_OPTIMIZE_FOR_SIZE).
>

The initial aim to add "-falign-functions=4 -falign-labels=4" is to
avoid generating nop instructions in .o file with -mrelax option
by default, otherwise the orc info can not match the symbol address
in vmlinux.

I want to add -mno-relax option and remove the extra option
"-falign-functions=4 -falign-labels=4", then the offsets in
each .o file and vmlinux are same, and it is not necessary
to do the special handling about local labels, I think
it will make life easier.

Thanks,
Tiezhu