linux-kernel - Re: [PATCH 5/5] MIPS: Implement MIPSr6 R_MIPS

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Date:	Wed, 3 Feb 2016 12:47:50 +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 5/5] MIPS: Implement MIPSr6 R_MIPS_PC2x rel-style relocs

On Wed, Feb 03, 2016 at 03:44:45AM +0000, Paul Burton wrote:
> MIPS32r6 code makes use of rel-stye relocations & may contain the new
> relocations R_MIPS_PC21_S2 or R_MIPS_PC26_S2 which were introduced with
> MIPSr6. Implement support for those relocations such that we can load
> MIPS32r6 kernel modules.
> 
> Signed-off-by: Paul Burton <paul.burton@...tec.com>

Looks good to me,
Reviewed-by: James Hogan <james.hogan@...tec.com>

Cheers
James

> 
> ---
> 
>  arch/mips/kernel/module.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 52 insertions(+)
> 
> diff --git a/arch/mips/kernel/module.c b/arch/mips/kernel/module.c
> index f2de9b8..d62fd56 100644
> --- a/arch/mips/kernel/module.c
> +++ b/arch/mips/kernel/module.c
> @@ -194,6 +194,56 @@ static int apply_r_mips_pc16_rel(struct module *me, u32 *location, Elf_Addr v)
>  	return 0;
>  }
>  
> +static int apply_r_mips_pc21_rel(struct module *me, u32 *location, Elf_Addr v)
> +{
> +	long offset;
> +
> +	if (v % 4) {
> +		pr_err("module %s: dangerous R_MIPS_PC21 REL relocation\n",
> +		       me->name);
> +		return -ENOEXEC;
> +	}
> +
> +	/* retrieve & sign extend implicit addend */
> +	offset = *location & 0x1fffff;
> +	offset |= (offset & BIT(20)) ? (~0l & ~0x1fffffl) : 0;
> +
> +	offset += ((long)v - (long)location) >> 2;
> +	if ((offset >> 20) > 0 || (offset >> 20) < -1) {
> +		pr_err("module %s: relocation overflow\n", me->name);
> +		return -ENOEXEC;
> +	}
> +
> +	*location = (*location & ~0x001fffff) | (offset & 0x001fffff);
> +
> +	return 0;
> +}
> +
> +static int apply_r_mips_pc26_rel(struct module *me, u32 *location, Elf_Addr v)
> +{
> +	long offset;
> +
> +	if (v % 4) {
> +		pr_err("module %s: dangerous R_MIPS_PC26 REL relocation\n",
> +		       me->name);
> +		return -ENOEXEC;
> +	}
> +
> +	/* retrieve & sign extend implicit addend */
> +	offset = *location & 0x3ffffff;
> +	offset |= (offset & BIT(25)) ? (~0l & ~0x3ffffffl) : 0;
> +
> +	offset += ((long)v - (long)location) >> 2;
> +	if ((offset >> 25) > 0 || (offset >> 25) < -1) {
> +		pr_err("module %s: relocation overflow\n", me->name);
> +		return -ENOEXEC;
> +	}
> +
> +	*location = (*location & ~0x03ffffff) | (offset & 0x03ffffff);
> +
> +	return 0;
> +}
> +
>  static int (*reloc_handlers_rel[]) (struct module *me, u32 *location,
>  				Elf_Addr v) = {
>  	[R_MIPS_NONE]		= apply_r_mips_none,
> @@ -202,6 +252,8 @@ static int (*reloc_handlers_rel[]) (struct module *me, u32 *location,
>  	[R_MIPS_HI16]		= apply_r_mips_hi16_rel,
>  	[R_MIPS_LO16]		= apply_r_mips_lo16_rel,
>  	[R_MIPS_PC16]		= apply_r_mips_pc16_rel,
> +	[R_MIPS_PC21_S2]	= apply_r_mips_pc21_rel,
> +	[R_MIPS_PC26_S2]	= apply_r_mips_pc26_rel,
>  };
>  
>  int apply_relocate(Elf_Shdr *sechdrs, const char *strtab,
> -- 
> 2.7.0
> 
> 

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