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Re: RFC: Add 32bit x86-64 support to binutils
- From: "Jan Beulich" <JBeulich at novell dot com>
- To: "Jakub Jelinek" <jakub at redhat dot com>, "H. Peter Anvin" <hpa at zytor dot com>
- Cc: "Joseph S. Myers" <joseph at codesourcery dot com>,<gcc at gcc dot gnu dot org>, "H.J. Lu" <hjl dot tools at gmail dot com>, <binutils at sourceware dot org>
- Date: Wed, 05 Jan 2011 07:46:17 +0000
- Subject: Re: RFC: Add 32bit x86-64 support to binutils
- References: <20101230182308.GA21296@intel.com> <Pine.LNX.4.64.1012301831270.30514@digraph.polyomino.org.uk> <AANLkTi=5rp8+1_h=Bt-FLnVW0mDY6N_tLb020XHr4d1n@mail.gmail.com> <Pine.LNX.4.64.1012301905400.30514@digraph.polyomino.org.uk> <AANLkTik6qXqKC8tEizXo1GrvEa7x9UGYaApN1n78Fa-b@mail.gmail.com> <AANLkTimUbL99QQaoAgaBHGctgtTurybP1DEjN8YbNXRt@mail.gmail.com> <4D21B5C1020000780002A0BC@vpn.id2.novell.com> <AANLkTikfLejXiegNNpgEgNQv5=pR8ZNy8zhF3Z0Z1tWR@mail.gmail.com> <4D23687E.3030207@zytor.com> <20110104200232.GD19887@sunsite.ms.mff.cuni.cz>
>>> On 04.01.11 at 21:02, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Jan 04, 2011 at 10:35:42AM -0800, H. Peter Anvin wrote:
>> On 01/04/2011 09:56 AM, H.J. Lu wrote:
>> >>
>> >> I think it is a gross misconception to tie the ABI to the ELF class of
>> >> an object. Specifying the ABI should imo be done via e_flags or
>> >> one of the unused bytes of e_ident, and in all reality the ELF class
>> >> should *only* affect the file layout (and 64-bit should never have
>> >> forbidden to use 32-bit ELF containers; similarly 64-bit ELF objects
>> >> may have uses for 32-bit architectures/ABIs, e.g. when debug
>> >> information exceeds the 4G boundary).
>> >
>> > I agree with you in principle. But I think it should be done via
>> > a new attribute section, similar to ARM.
>> >
>>
>> Oh god, please, no.
>>
>> I have to say I'm highly questioning to Jan's statement in the first
>> place. Crossing 32- and 64-bit ELF like that sounds like a kernel
>> security hole waiting to happen.
A particular OS/kernel has the freedom to not implement support for
other than the default format. But having the ABI disallow it
altogether certainly isn't the right choice. And yes, we had been
allowing cross-bitness ELF in an experimental (long canceled) OS
of ours.
> Yeah, and there are other targets where the elf class determines ABI
> too (e.g. EM_S390 is used for both 31-bit and 64-bit binaries and
> the ELF class determines which).
So the usual thing is going to happen - someone made a mistake (I'm
convinced the ELF class was never meant to affect anything but the
file format), and this gets taken as an excuse to let the mistake
spread.
Jan