linux-kernel - Re: [PATCH 4/5] MIPS: Support R_MIPS

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Message-ID: <20160203124940.GE5464@jhogan-linux.le.imgtec.org>
Date:	Wed, 3 Feb 2016 12:49:40 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Paul Burton <paul.burton@...tec.com>
CC:	<linux-mips@...ux-mips.org>, Ralf Baechle <ralf@...ux-mips.org>,
	"Andrey Konovalov" <adech.fo@...il.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	<linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 4/5] MIPS: Support R_MIPS_PC16 rel-style reloc

On Wed, Feb 03, 2016 at 03:44:44AM +0000, Paul Burton wrote:
> MIPS32 code uses rel-style relocs, and MIPS32r6 modules may include the
> R_MIPS_PC16 relocation. We thus need to support R_MIPS_PC16 rel-style
> relocations in order to load MIPS32r6 kernel modules. This patch adds
> such support, which is similar to the rela-style R_MIPS_PC16 support but
> making use of the implicit addend from the instruction encoding.
> 
> Signed-off-by: Paul Burton <paul.burton@...tec.com>
> ---
> 
>  arch/mips/kernel/module.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/kernel/module.c b/arch/mips/kernel/module.c
> index 2adf572..f2de9b8 100644
> --- a/arch/mips/kernel/module.c
> +++ b/arch/mips/kernel/module.c
> @@ -183,13 +183,25 @@ out_danger:
>  	return -ENOEXEC;
>  }
>  
> +static int apply_r_mips_pc16_rel(struct module *me, u32 *location, Elf_Addr v)
> +{
> +	u16 val;
> +
> +	val = *location;
> +	val += (v - (Elf_Addr)location) >> 2;
> +	*location = (*location & 0xffff0000) | val;

Looks correct, but presumably this could benefit from some sanity
checking like the other patches.

Cheers
James

> +
> +	return 0;
> +}
> +
>  static int (*reloc_handlers_rel[]) (struct module *me, u32 *location,
>  				Elf_Addr v) = {
>  	[R_MIPS_NONE]		= apply_r_mips_none,
>  	[R_MIPS_32]		= apply_r_mips_32_rel,
>  	[R_MIPS_26]		= apply_r_mips_26_rel,
>  	[R_MIPS_HI16]		= apply_r_mips_hi16_rel,
> -	[R_MIPS_LO16]		= apply_r_mips_lo16_rel
> +	[R_MIPS_LO16]		= apply_r_mips_lo16_rel,
> +	[R_MIPS_PC16]		= apply_r_mips_pc16_rel,
>  };
>  
>  int apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
> -- 
> 2.7.0
> 
> 

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