linux-kernel - Re: [PATCH v1 3/3] LoongArch: Fix unreachable instruction warnings about entry functions

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Message-ID: <93a93bcf-8778-a6a3-142d-c8aeb3cee5cd@loongson.cn>
Date: Thu, 4 Sep 2025 09:26:43 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: Josh Poimboeuf <jpoimboe@...nel.org>, Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, Nathan Chancellor <nathan@...nel.org>,
 loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/3] LoongArch: Fix unreachable instruction warnings
 about entry functions

On 2025-09-04 03:22, Josh Poimboeuf wrote:

> On Mon, Sep 01, 2025 at 03:21:56PM +0800, Tiezhu Yang wrote:
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -3,8 +3,6 @@
>>   # Makefile for the Linux/LoongArch kernel.
>>   #
>>   
>> -OBJECT_FILES_NON_STANDARD_head.o := y
>> -
>>   always-$(KBUILD_BUILTIN)	:= vmlinux.lds
>>   
>>   obj-y		+= head.o cpu-probe.o cacheinfo.o env.o setup.o entry.o genex.o \
>> diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S
>> index e3865e92a917..a11880f3a7e1 100644
>> --- a/arch/loongarch/kernel/head.S
>> +++ b/arch/loongarch/kernel/head.S
>> @@ -42,6 +42,7 @@ SYM_DATA(kernel_fsize, .long _kernel_fsize);
>>   	.align 12
>>   
>>   SYM_CODE_START(kernel_entry)			# kernel entry point
>> +	UNWIND_HINT_UNDEFINED
> Should this not be UNWIND_HINT_END_OF_STACK?
>
> I notice Loongarch doesn't seem to use that anywhere.  How does any ORC
> unwind succeed?
IIRC, unwinder stops when fail when call __kernel_text_address(bt_address),
or success when call 
arch/loongarch/kernel/unwind_orc.c::is_entry_func(bt_address).
> UNWIND_HINT_UNDEFINED sets an error condition which
> should cause a livepatch transition to stall.
>