Bug#724320: gmp: x32: sizeof(mp_limb_t)!=sizeof(void*) is not supported by GAP and PARI

Vincent Lefevre vincent at vinc17.net
Wed Oct 2 23:03:44 CEST 2013

On 2013-10-02 09:16:10 -0700, Daniel Schepler wrote:
> Is your kernel built with x32 support?  (Check for CONFIG_X86_X32=y in 
> /boot/config-*.)

It doesn't, and there's actually a RFE:


but it's not enabled for "security" reasons (I won't discuss that).

> Anyway, to rephrase what others have already said, -m32 compiles to an i386 
> executable, which runs in compatibility mode from which x86_64 instructions 
> aren't available.  Which explains why trying to force ABI=x32 with -m32 
> results in failing assembly; and if you disable assembly, it uses the gcc 
> version of 64-bit multiplication which simulates it using 3 or 4 32-bit 
> multiplications, which explains why it's so slow.

Since the goal is just for testing, this is not a big problem.

> I agree with the comments on the original question: if GAP and PARI
> don't support sizeof(mp_limb_t) > sizeof(long), then it makes most
> sense just to say they're not supported on x32 at the moment.

There may be other software having similar problems, possibly not
by design like with PARI, but just because this hasn't been tested,
just like it's difficult to test programs with CHAR_BIT > 8. :)
I would be surprised if there aren't any other examples.

In particular I don't know yet if MPFR behaves correctly (it had
problems related to different type size in the past).

Another thing for all recipients: Torbjorn complained that mail he
receives from me in this thread has a truncated Mail-Followup-To.
For instance, on my mail sent on

  Date: Wed, 2 Oct 2013 11:38:26 +0200

here, he had only his address in the Mail-Followup-To, while I can
see in the copy I've received from the gmp-discuss list that the
Mail-Followup-To is complete (4 addresses); thus the problem can
only occur after the mail is forwarded by the mailing-list server.
Could you check on your side please, if you have the same problem
as Torbjorn?

Vincent Lefèvre <vincent at vinc17.net> - Web: <http://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

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