linux-kernel - Re: [PATCH] LoongArch: Record pc instead of offset in la-abs relocation

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Message-ID: <20231120230817.GA2116806@dev-arch.thelio-3990X>
Date:   Mon, 20 Nov 2023 16:08:17 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     WANG Rui <wangrui@...ngson.cn>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Jinyang He <hejinyang@...ngson.cn>,
        Xi Ruoyao <xry111@...111.site>, linux-kernel@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-kbuild@...r.kernel.org,
        llvm@...ts.linux.dev, loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH] LoongArch: Record pc instead of offset in la-abs
 relocation

Hi Rui,

On Thu, Nov 16, 2023 at 09:03:31PM +0800, WANG Rui wrote:
> To clarify, the previous version functioned flawlessly. However, it's
> worth noting that the LLVM's LoongArch backend currently lacks support
> for cross-section label calculations. With this patch, we enable the use
> of clang to compile relocatable kernels.
> 
> Signed-off-by: WANG Rui <wangrui@...ngson.cn>

Thanks a lot for the patch! This fixes the CONFIG_RELOCATABLE build for
me as well.

Tested-by: Nathan Chancellor <nathan@...nel.org>

Something I noticed while testing is that a kernel linked with ld.lld
does not boot while one linked with ld.bfd did. I think this might be
the same issue that Xuerui filed on our issue tracker but I figured I
would mention it in case not:
https://github.com/ClangBuiltLinux/linux/issues/1883

Cheers,
Nathan

> ---
>  arch/loongarch/include/asm/asmmacro.h | 3 +--
>  arch/loongarch/include/asm/setup.h    | 2 +-
>  arch/loongarch/kernel/relocate.c      | 2 +-
>  3 files changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/loongarch/include/asm/asmmacro.h b/arch/loongarch/include/asm/asmmacro.h
> index c9544f358c33..655db7d7a427 100644
> --- a/arch/loongarch/include/asm/asmmacro.h
> +++ b/arch/loongarch/include/asm/asmmacro.h
> @@ -609,8 +609,7 @@
>  	lu32i.d	\reg, 0
>  	lu52i.d	\reg, \reg, 0
>  	.pushsection ".la_abs", "aw", %progbits
> -	768:
> -	.dword	768b-766b
> +	.dword	766b
>  	.dword	\sym
>  	.popsection
>  #endif
> diff --git a/arch/loongarch/include/asm/setup.h b/arch/loongarch/include/asm/setup.h
> index a0bc159ce8bd..ee52fb1e9963 100644
> --- a/arch/loongarch/include/asm/setup.h
> +++ b/arch/loongarch/include/asm/setup.h
> @@ -25,7 +25,7 @@ extern void set_merr_handler(unsigned long offset, void *addr, unsigned long len
>  #ifdef CONFIG_RELOCATABLE
>  
>  struct rela_la_abs {
> -	long offset;
> +	long pc;
>  	long symvalue;
>  };
>  
> diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c
> index 6c3eff9af9fb..288b739ca88d 100644
> --- a/arch/loongarch/kernel/relocate.c
> +++ b/arch/loongarch/kernel/relocate.c
> @@ -52,7 +52,7 @@ static inline void __init relocate_absolute(long random_offset)
>  	for (p = begin; (void *)p < end; p++) {
>  		long v = p->symvalue;
>  		uint32_t lu12iw, ori, lu32id, lu52id;
> -		union loongarch_instruction *insn = (void *)p - p->offset;
> +		union loongarch_instruction *insn = (void *)p->pc;
>  
>  		lu12iw = (v >> 12) & 0xfffff;
>  		ori    = v & 0xfff;
> -- 
> 2.42.1
> 
>