linux-kernel - Re: [RFC PATCH 2/2] objtool/LoongArch: Fix unreachable instruction warnings about head.S

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Message-ID: <8dfe8bde-0095-d6c3-b9ca-cce2bf720ac2@loongson.cn>
Date: Tue, 26 Aug 2025 20:27:13 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Huacai Chen <chenhuacai@...nel.org>, Josh Poimboeuf
 <jpoimboe@...nel.org>, Nathan Chancellor <nathan@...nel.org>,
 loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] objtool/LoongArch: Fix unreachable instruction
 warnings about head.S

On 2025/8/26 下午4:20, Peter Zijlstra wrote:
> On Tue, Aug 26, 2025 at 02:46:31PM +0800, Tiezhu Yang wrote:
>> When compiling with LLVM and CONFIG_LTO_CLANG is set, there exist the
>> following objtool warnings after silencing all of the other warnings:

...

>> Just give a proper unwind hint to silence the above warnings. By the way,
>> the previous instructions of kernel_entry+0xf4 and smpboot_entry+0x68 are
>> the 'bl' instructions, the call destination symbols are start_kernel() and
>> start_secondary() which are noreturn functions, then the 'bl' instructions
>> are marked as dead end in annotate_call_site(), so actually ASM_BUG() can
>> be removed due to unnecessary, otherwise there are following warnings:

...

>> Link: https://lore.kernel.org/lkml/20250814083651.GR4067720@noisy.programming.kicks-ass.net/
>> Suggested-by: Peter Zijlstra <peterz@...radead.org>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>> ---
>>   arch/loongarch/kernel/head.S | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> At this point you should also be able to remove that Makefile thing,
> right?

Yes, you are right, will do it in the next version if this patch
makes sense.

Thanks,
Tiezhu