linux-kernel - Re: [PATCH] riscv: kexec: Cleanup riscv_kexec

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Date:   Thu, 31 Aug 2023 14:55:54 +0800
From:   Song Shuai <songshuaishuai@...ylab.org>
To:     Andreas Schwab <schwab@...e.de>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, mick@....forth.gr, alex@...ti.fr,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: kexec: Cleanup riscv_kexec_relocate

Hi, Andreas:

在 2023/8/30 15:24, Andreas Schwab 写道:
> On Aug 30 2023, Song Shuai wrote:
> 
>> @@ -52,21 +42,27 @@ SYM_CODE_START(riscv_kexec_relocate)
>>   	 * the start of the loop below so that we jump there in
>>   	 * any case.
>>   	 */
>> -	la	s8, 1f
>> -	sub	s8, s8, s7
>> -	csrw	CSR_STVEC, s8
>> +	la	s6, 1f
>> +	sub	s6, s6, s4
>> +	csrw	CSR_STVEC, s6
>> +
>> +	/*
>> +	 * With C-extension, here we get 42 Bytes and the next
>> +	 * .align directive would pad zeros here up to 44 Bytes.
>> +	 * So manually put a nop here to avoid zeros padding.
>> +	*/
>> +	nop
>>   
>>   	/* Process entries in a loop */
>>   .align 2
> 
> While you are at it, I'd suggest being explicit about .palign
> vs. .balign.
> 
How about this commemt:

Due to the stvec.BASE 4-byte alignment constraint, the following .align
(alias of .p2align) directive will align the next instruction to
a 4-byte boundary by padding zeros for this .rodata section.

With C-extension, here we get 42 Bytes and would be padded with zeros
up to 44 Bytes. So manually put a nop here to avoid it.

-- 
Thanks
Song Shuai