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Re: [PATCH] fix modpost segfault for 64bit mipsel kernel

To: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Subject: Re: [PATCH] fix modpost segfault for 64bit mipsel kernel
From: Thiemo Seufer <ths@networkno.de>
Date: Thu, 20 Apr 2006 01:19:00 +0100
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org, sam@ravnborg.org
In-reply-to: <20060419.112228.108306767.anemo@mba.ocn.ne.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20060417140735.GC28935@networkno.de> <20060418.004718.108120830.anemo@mba.ocn.ne.jp> <20060417162742.GD28935@networkno.de> <20060419.112228.108306767.anemo@mba.ocn.ne.jp>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.5.11+cvs20060403
Atsushi Nemoto wrote:
> On Mon, 17 Apr 2006 17:27:42 +0100, Thiemo Seufer <ths@networkno.de> wrote:
> > So it is the
> > 
> >       r.r_info   = TO_NATIVE(rela->r_info);
> > 
> > in modpost.c which breaks both SYM and TYPE because it assumes a
> > 64bit integer. The proper solution would be to add a Elf64_Mips_Rela
> > structure (with lots of nearly identical duplicated code), the hack
> > would be to cast r_info to a 32bit integer for mips, before feeding
> > it to TO_NATIVE (which works until somebody asks for the TYPE, then
> > a separate mips64 version becomes inevitable.)
> 
> I'd like to fix in _proper_ way.  Please review.  Thanks.
> 
> 
> 64bit mips has different r_info layout.  This patch fixes modpost
> segfault for 64bit little endian mips kernel.
> 
> Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> 
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index cd00e9f..4ce95c6 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -710,7 +710,20 @@ static void check_sec_ref(struct module 
>                       Elf_Rela r;
>                       const char *secname;
>                       r.r_offset = TO_NATIVE(rela->r_offset);
> +#if KERNEL_ELFCLASS == ELFCLASS64
> +                     if (hdr->e_machine == EM_MIPS) {
> +                             unsigned int r_sym =
> +                                     ELF64_MIPS_R_SYM(rela->r_info);
> +                             unsigned int r_type =
> +                                     ELF64_MIPS_R_TYPE(rela->r_info);
> +                             r.r_info = ELF_R_INFO(TO_NATIVE(r_sym),
> +                                                   TO_NATIVE(r_type));
[snip]
> +/* The 64-bit MIPS ELF ABI uses an unusual reloc format. */
> +typedef struct
> +{
> +  Elf32_Word    r_sym;               /* Symbol index */
> +  unsigned char r_ssym;              /* Special symbol for 2nd relocation */
> +  unsigned char r_type3;     /* 3rd relocation type */
> +  unsigned char r_type2;     /* 2nd relocation type */
> +  unsigned char r_type1;     /* 1st relocation type */
> +} _Elf64_Mips_R_Info;
[snip]
> +#define ELF64_MIPS_R_TYPE(i) \
> +  (((_Elf64_Mips_R_Info_union)(i)).r_info_fields.r_type1 \
> +   | ((Elf32_Word)(__extension__ (_Elf64_Mips_R_Info_union)(i) \
> +                ).r_info_fields.r_type2 << 8) \
> +   | ((Elf32_Word)(__extension__ (_Elf64_Mips_R_Info_union)(i) \
> +                ).r_info_fields.r_type3 << 16) \
> +   | ((Elf32_Word)(__extension__ (_Elf64_Mips_R_Info_union)(i) \
> +                ).r_info_fields.r_ssym << 24))

Why is it the right thing to combine the type info into a 32bit word?
It will never get used as such for MIPS ELF64. I would have expected
something like:

#define ELF64_MIPS_R_INFO(sym,ssym,t3,t2,t1)            \
{(                                                      \
        _Elf64_Mips_R_Info info = {                     \
                .r_sym = sym,                           \
                .r_ssym = ssym,                         \
                .r_type3 = t3,                          \
                .r_type2 = t2,                          \
                .r_type1 = t1,                          \
        }                                               \
        (Elf64_Xword)info;                              \
)}

without a corresponding ELF64_MIPS_R_TYPE, and then:

        if (hdr->e_ident[EI_CLASS] == ELFCLASS64
            && hdr->e_machine == EM_MIPS) {
                _Elf64_Mips_R_Info info = (_Elf64_Mips_R_Info)r.r_info;
                r.r_info = ELF64_MIPS_R_INFO(TO_NATIVE(info.r_sym),
                                             info.r_ssym, info.r_type3,
                                             info.r_type2, info.r_type1);
        }


Thiemo

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