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Postings from March 2003
On Sat, Mar 01, 2003 at 10:57:51PM +0200, Jarkko Hietaniemi wrote:
> Here's an attempt to squash the glibc _moddi3 negative quad bug that's
> been around for aeons. An aeon. Almost a year. (The bug is also
> known as [perl #9402] or "Abigail's faithfully failing int.t".)
> I didn't feel like writing a Configure test for such a precise bug
> but instead went for runtime. Now pp_i_modulo is basically a switchboard
> that rewires the opcode dispatch table as required (thus effectively
> rewiring itself out of the way). The patch works for me-- I've got
> the same buggy glibc in the Debian box I run my smokes in.
>
Nice hack, however don't you also want to replace
PL_op->op_ppaddr so that the next time this OP executes it will use the
direct version, since the PL_peepaddr is only used for new ops since
runops does while ((PL_op = CALL_FPTR(PL_op->op_ppaddr)(aTHX))) {
> --- pp.c.orig 2003-03-01 22:51:50.000000000 +0200
> +++ pp.c 2003-03-01 22:51:55.000000000 +0200
> @@ -2457,6 +2457,40 @@
> }
> }
>
> +STATIC
> +PP(pp_i_modulo_0)
> +{
> + /* This is the vanilla old i_modulo. */
> + dSP; dATARGET; tryAMAGICbin(modulo,opASSIGN);
> + {
> + dPOPTOPiirl;
> + if (!right)
> + DIE(aTHX_ "Illegal modulus zero");
> + SETi( left % right );
> + RETURN;
> + }
> +}
> +
> +STATIC
> +PP(pp_i_modulo_1)
> +{
> +#ifdef __GLIBC__
> + /* This is the i_modulo with the workaround for the _moddi3
> + * bug in (at least) glibc 2.2.5 (the "right = -right" part
> + * is the workaround). See below for pp_i_modulo. */
> + dSP; dATARGET; tryAMAGICbin(modulo,opASSIGN);
> + {
> + dPOPTOPiirl;
> + if (!right)
> + DIE(aTHX_ "Illegal modulus zero");
> + if (right < 0)
> + right = -right;
> + SETi( left % right );
> + RETURN;
> + }
> +#endif
> +}
> +
> PP(pp_i_modulo)
> {
> dSP; dATARGET; tryAMAGICbin(modulo,opASSIGN);
> @@ -2464,6 +2498,28 @@
> dPOPTOPiirl;
> if (!right)
> DIE(aTHX_ "Illegal modulus zero");
> + /* The assumption is to use hereafter the old vanilla version... */
> + PL_ppaddr[OP_I_MODULO] = &Perl_pp_i_modulo_0;
+ PL_op->op_ppaddr = &Perl_pp_i_modulo_0;
> + /* .. but if we have glibc, we might have a buggy _moddi3
> + * (at least glicb 2.2.5 is known to have this bug), in other
> + * words our integer modulus with negative quad as the second
> + * argument might be broken. Test for this and re-patch the
> + * opcode dispatch table if that is the case, remembering to
> + * also apply the workaround so that this first round works
> + * right, too.
> + *
> + * See [perl #9402] for more information. */
> +#if defined(__GLIBC__) && IVSIZE == 8
> + {
> + IV l = 3;
> + IV r = -10;
> + if (l % r == -3) {
> + PL_ppaddr[OP_I_MODULO] = &Perl_pp_i_modulo_1;
PL_op->op_ppaddr = &Perl_pp_i_modulo_1;
> + if (right < 0)
> + right = -right;
> + }
> + }
> +#endif
> SETi( left % right );
> RETURN;
> }
>
> --
> Jarkko Hietaniemi <jhi@iki.fi> http://www.iki.fi/jhi/ "There is this special
> biologist word we use for 'stable'. It is 'dead'." -- Jack Cohen
Yes this is threadsafe.
Arthur
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