Problem with Guile on ia64 (possibly "getcontext" related)

Problem with Guile on ia64 (possibly "getcontext" related)

[Rob Browning]

Guile 1.6.8 is crashing on ia64 with an illegal instruction whenever
it tries to execute call-with-current-continuation.  For those who
don't know, call-with-current-continuation captures the current state
of the computation; it's a language feature somewhat similar to
setjmp.

The crash seems to be right around an asm "getcontext" call, and after
looking around, I found these two links:

  http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/144939
  http://lists.freebsd.org/pipermail/freebsd-sparc64/2006-January/003739.html

They appear claim that adding a dummy (non-executed) setjmp just after
the getcontext call will fix the problem because gcc recognizes
setjmp, but not getcontext, and makes appropriate arrangements.

So I tried adding a dummy setjmp just after the getcontext call, and
that does fix the problem.

However, even though this worked, I'd still prefer to have a better
idea that this is the right fix before adopting it.  Is that likely?

The relevant function is scm_make_continuation which you can find
here:

  http://cvs.savannah.gnu.org/viewcvs/guile/guile-core/libguile/continuations.c?rev=1.38.2.7&root=guile&only_with_tag=branch_release-1-6&view=markup

Versions:

  Debian libc6.1 2.3.6-15
  Debian gcc (GCC) 4.1.2 20060708 (prerelease) (Debian 4.1.1-8)

Thanks

-- 
Rob Browning
rlb @defaultvalue.org and @debian.org; previously @cs.utexas.edu
GPG starting 2002-11-03 = 14DD 432F AE39 534D B592  F9A0 25C8 D377 8C7E 73A4


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Re: Problem with Guile on ia64 (possibly "getcontext" related)

[Keith Owens]

Rob Browning (on Sat, 15 Jul 2006 15:24:31 -0700) wrote:
>
>Guile 1.6.8 is crashing on ia64 with an illegal instruction whenever
>it tries to execute call-with-current-continuation.  For those who
>don't know, call-with-current-continuation captures the current state
>of the computation; it's a language feature somewhat similar to
>setjmp.
>
>The crash seems to be right around an asm "getcontext" call, and after
>looking around, I found these two links:
>
>  http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/144939
>  http://lists.freebsd.org/pipermail/freebsd-sparc64/2006-January/003739.html
>
>They appear claim that adding a dummy (non-executed) setjmp just after
>the getcontext call will fix the problem because gcc recognizes
>setjmp, but not getcontext, and makes appropriate arrangements.
>
>So I tried adding a dummy setjmp just after the getcontext call, and
>that does fix the problem.
>
>However, even though this worked, I'd still prefer to have a better
>idea that this is the right fix before adopting it.  Is that likely?
>>
>The relevant function is scm_make_continuation which you can find
>here:
>
>  http://cvs.savannah.gnu.org/viewcvs/guile/guile-core/libguile/continuations.c?rev=1.38.2.7&root=guile&only_with_tag=branch_release-1-6&view=markup

Wild guess, based on no data.  Add '__attribute__ ((returns_twice))' to
the definition of ia64_getcontext.  That should remove the need to use
setjmp.

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Re: Problem with Guile on ia64 (possibly "getcontext" related)

[Rob Browning]

Keith Owens <kaos@ocs.com.au> writes:

> Wild guess, based on no data.  Add '__attribute__ ((returns_twice))' to
> the definition of ia64_getcontext.  That should remove the need to use
> setjmp.

That also seems to fix the crash.

So would it be correct to say that the likely problem is just that
because Guile calls getcontext via asm, gcc doesn't know that the call
needs to be handled specially?

Thanks
-- 
Rob Browning
rlb @defaultvalue.org and @debian.org; previously @cs.utexas.edu
GPG starting 2002-11-03 = 14DD 432F AE39 534D B592  F9A0 25C8 D377 8C7E 73A4
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the body of a message to majordomo@vger.kernel.org
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Re: Problem with Guile on ia64 (possibly "getcontext" related)

[Keith Owens]

Rob Browning (on Tue, 18 Jul 2006 18:40:07 -0700) wrote:
>Keith Owens <kaos@ocs.com.au> writes:
>
>> Wild guess, based on no data.  Add '__attribute__ ((returns_twice))' to
>> the definition of ia64_getcontext.  That should remove the need to use
>> setjmp.
>
>That also seems to fix the crash.

Good.

>So would it be correct to say that the likely problem is just that
>because Guile calls getcontext via asm, gcc doesn't know that the call
>needs to be handled specially?

Exactly right.



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