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Date:	Tue, 8 Feb 2011 13:14:46 +0100
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Subject:	Re: TP_NUM_C_BUFS too small
From:	marco atzeri <marco DOT atzeri AT gmail DOT com>
To:	cygwin AT cygwin DOT com
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On Tue, Feb 8, 2011 at 12:59 PM, Corinna Vinschen  wrote:
> On Feb =A07 22:38, marco atzeri wrote:
>> I am testing latest release candidate for octave, and only on cygwin usi=
ng
>> the fltk graphics interface when we try to print through ghostscript we =
have:
>>
>> octave 4236 E:\cygwin2\bin\octave-3.3.92.exe: *** fatal error -
>> Internal error: TP_NUM_C_BUFS too small: 79987540 > 10
>
> This message points to a stack corruption. =A0There's a thread-local
> storage in the highest area of the thread local stack. =A0In this TLS area
> are a couple of buffer pointers which point to mallocated storage.
> There are up to 10 of the "C_BUF" pointers and a counter which contains
> the number of used pointers. =A0That counter has the value 79987540, which
> looks *very* wrong.

I was sure .

>
>> Stack trace:
>> Frame =A0 =A0 Function =A0Args
>> 0022CF90 =A06102773B =A0(0022CF90, 00000000, 00000000, 00000000)
>> 0022D280 =A06102773B =A0(6117CC60, 00008000, 00000000, 6117E997)
>> 0022E2B0 =A061004E5B =A0(611C978C, 04C48354, 0000000A, 0022E4E4)
>> 0022E2D0 =A0610EF554 =A0(0022F578, 00000001, 00000000, 00000000)
>> 0022F5A0 =A061096D4F =A0(61208220, 0002625A, 00001000, 000BF399)
>> 011AE3F4 =A0610225C2 =A0(6F2F6572, 76617463, 2E332F65, 32392E33)
>> End of stack trace
>> Hangup
>>
>> This is on latest cygwin snapshot, but it crash on any version release.
>
> So this occurs on 1.7.7 as well?

any  1.7.x or snapshots that I tested in the last 6 months, since fltk
1.1.10-1 was available.
This crash always happens, and it seems a specific cygwin only issue.

>> I suspect the error message is a red herring. Am I right ?
>
> Yes, it is. =A0The problem is that the stackdump is not very helpful
> to find the cause. =A0The information you can gather is where the problem
> is encountered, but it doesn't show what overwrote the TLS area.
>
>> The plot is built as expected, so gs is doing its work; from strace outp=
ut
>> (available on http://matzeri.altervista.org/works/octave/)
>
> There's nothing in octave_fltk.strace which points to any kind of
> problem.

thanks for looking

>
>> I guess that gs execution is unable to return back on octave.
>>
>> Suggestion for debugging ?
>
> Build the Cygwin DLL for debugging (just -g, no -O2), build octave for
> debugging, and try to find the problem.
>
> What I can see from the stack dump is that it happens when trying to
> open a file. =A0If you find the Cygwin call (probably, but not necessarily
> open()) from octave in which the problem is encountered, you can narrow
> down the problem to somewhere between this call and the previous
> file-related call since all of these calls access the TLS buffers. =A0From
> there it's detective work. =A0Maybe a watchpoint on the aforementioned
> counter helps (class tls_pathbuf, member c_cnt).
>
> This is pretty tricky to find, I fear.

Time to learn serious gdb debugging.

>
>
> Corinna
>

thanks
Marco

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