linux-kernel - Re: [PATCH v2 2/5] LoongArch: Use la.pcrel instead of la.abs for exception handlers

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Date:   Wed, 8 Feb 2023 08:59:19 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Xi Ruoyao <xry111@...111.site>,
        Youling Tang <tangyouling@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>
Cc:     Xuerui Wang <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] LoongArch: Use la.pcrel instead of la.abs for
 exception handlers


On 2023-02-07 22:39, Xi Ruoyao wrote:
> On Tue, 2023-02-07 at 22:28 +0800, Xi Ruoyao wrote:
>> +struct handler_reloc *eentry_reloc[128] = {
>> +       [0] = NULL, /* merr handler */
> Self review:
>
> This is actually incorrect.  Currently the merr handler (except_vec_cex)
> is coded as:
>
> SYM_FUNC_START(except_vec_cex)
>          b       cache_parity_error
> SYM_FUNC_END(except_vec_cex)
>
> Once this is copied into the per-cpu handler page, the offset (coded in
> the b instruction) will be absolutely wrong.  But it's already incorrect
> in the current mainline, and I'm not familiar with CSR.CRMD.DA=1
> configuration so I'm not sure how to fix it.
>
It bothers me, too. And I've mentioned it to Huacai offline before.
Besides, after fixing this issue I'll support a series of patches
to fix the cfi note in asm files.