#12873: Clear FPU in i386/x86_64 longjmp()
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Reporter: jdemeyer | Owner: jdemeyer
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: c_lib | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Jeroen Demeyer | Merged in:
Dependencies: | Stopgaps:
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Description changed by jdemeyer:
Old description:
> The libc `setjmp`/`longjmp` functions on i686 hardware do not restore the
> x87 FPU state, in particular when MMX instructions have been used. On
> Linux and OS X 10.6, the FPU state is restored when an interrupt occurs,
> but on Solaris this is not the case.
>
> The proposed solution is to clear the FPU state (using the `EMMS`
> instruction) in the signal handler. For more context, see #12777 where
> this bug was discovered.
>
> To see the problem in action, compile [attachment:emms.c] on i686
> hardware with
> {{{
> gcc -march=pentium2 -m32 -mfpmath=387 -lm emms.c -o emms
> }}}
>
> '''Apply''' [attachment:12873_emms.patch]
New description:
The libc `setjmp`/`longjmp` functions on i386/x86_64 hardware do not
restore the 387 FPU state, in particular when MMX instructions have been
used. On Linux and OS X 10.6, the FPU state is restored when an interrupt
occurs, but on Solaris this is not the case.
The proposed solution is to clear the FPU (using the `EMMS` or `FFREE`
instructions) in the signal handler. For more context, see #12777 where
this bug was discovered.
To see the problem in action, compile [attachment:emms.c] on i686 hardware
with
{{{
gcc -march=pentium2 -m32 -mfpmath=387 -lm emms.c -o emms
}}}
'''Apply''' [attachment:12873_emms.patch]
--
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12873#comment:9>
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