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Re: [patch] linux: RFC: elf_check_arch() rework

To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Subject: Re: [patch] linux: RFC: elf_check_arch() rework
From: Carsten Langgaard <carstenl@mips.com>
Date: Thu, 25 Jul 2002 15:29:12 +0200
Cc: linux-mips@fnet.fr, linux-mips@oss.sgi.com
References: <Pine.GSO.3.96.1020725125830.27463H-100000@delta.ds2.pg.gda.pl>
Sender: owner-linux-mips@oss.sgi.com
"Maciej W. Rozycki" wrote:

> On Wed, 24 Jul 2002, Carsten Langgaard wrote:
>
> > We at MIPS are in the process of making an ABI spec for all this, which
> > is the intention that should be used by the tool-vendors.  So please
> > don't change the ELF header defines.
>
>  It'd be better the spec matched the real world...

Shouldn't it be the other way around, the real world should follow the spec
;-)
The whole ELF header definition is just one big mess, because we are lacking
a proper ABI spec.
That's what has motivated us, to begin making this ABI spec.

We have defined the e_flags this way:

/* ELF header e_flags defines. MIPS architecture level. */
#define EF_MIPS_ARCH_1      0x00000000  /* -mips1 code.  */
#define EF_MIPS_ARCH_2      0x10000000  /* -mips2 code.  */
#define EF_MIPS_ARCH_3      0x20000000  /* -mips3 code.  */
#define EF_MIPS_ARCH_4      0x30000000  /* -mips4 code.  */
#define EF_MIPS_ARCH_5      0x40000000  /* -mips5 code.  */
#define EF_MIPS_ARCH_32     0x60000000  /* MIPS32 code.  */
#define EF_MIPS_ARCH_64     0x70000000  /* MIPS64 code.  */
#define EF_MIPS_ARCH_32R2   0x80000000  /* MIPS32 code.  */
#define EF_MIPS_ARCH_64R2   0x90000000  /* MIPS64 code.  */

The missing value 0x50000000, is because IRIX has defined a EF_MIPS_ARCH_6
and Algorithmics has a E_MIPS_ARCH_ALGOR_32, which has this value.
If you look at the elf.h file in glibc, the you will see, it has the same
values as the kernel.

So I would prefer we fix that in binutils, I guess it not a problem as long
as you don't have a toolchain that can generate MIPS32 or MIPS64 code.


>
> > I don't see that is wrong with checking the ISA level, I rather have an
> > error telling me that I can't execute a certain ISA level than
> > eventually getting a reserved instruction or something worse like
> > something unpredictable.
>
>  Well, -ENOEXEC in not any more useful than SIGILL -- with the latter you
> have at least an idea what happened.  The ISA check is not implemented for
> any Linux port, so there no suitable hook in binfmt_*.c files.  You might
> propose an implementation if that's particularly important for you.
>

I would like a message telling me that I can't run this ISA level on the
system.
Imagined what would happen, if you execute mips3 code and execute ld/sd
instructions on a mips32 kernel (but on a 64-bit processor), the kernel only
save half the register and then everything could happen.


>
> > You are obviously right about the elf_check_arch in the 64-bit part of
> > the kernel is broken.  It's probably just be copied from the 32-bit part
> > without changes, like a lot of the code in the 64-bit kernel is.
>
>  Possibly, but it still makes me wonder why it wasn't adjusted at the time
> binfmt_elf32.c was created...
>
>   Maciej
>
> --
> +  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
> +--------------------------------------------------------------+
> +        e-mail: macro@ds2.pg.gda.pl, PGP key available        +

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