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Re^12: Segfault on second (identical) call to a sub

by BrowserUk (Patriarch)
on Feb 07, 2006 at 07:23 UTC ( [id://528437]=note: print w/replies, xml ) Need Help??


in reply to Re^11: Segfault on second (identical) call to a sub
in thread Segfault on second (identical) call to a sub

and I wish you had pointed it out sooner :-)

I wish I'd noticed it earlier :) It was only by comparing your Inline C to the XS that it stood out. Previously I'd just checked that allocs and frees were being done with XS macros and not crt functions.

Thanks again for your help.

It's unclear to me how 'len' gets assigned the appropriate value for when it's needed

I wondered that too, but if you unwind the SvPV() macro, you eventually realise that the len parameter passed to it is not used to indicate the length of anything, but rather is used to retrieve the length of the data held in the SV. This is done using the SvCUR() macro. It takes a bit of unwinding and could probably bear a mention in perlapi.

I've updated GD.xs 2.30 locally with this and got rid of a few unused var warnings which allowed it to compile clean and pass it's test suit. I then thrashed it for a while calling the OP sub and another like it that used GD2 data in a loop and it seems fine.

I've generated a patch against 2.30 and sent it directly to L.Stein along with a warning that I don't really know what I am doing with this stuff.


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Re^13: Segfault on second (identical) call to a sub
by syphilis (Archbishop) on Feb 07, 2006 at 09:03 UTC
    I wondered that too, but if you unwind the SvPV() macro, you eventually realise that the len parameter passed to it is not used to indicate the length of anything, but rather is used to retrieve the length of the data held in the SV.

    Come to think about it ... I think I've seen that alluded to before. Hopefully it will stick with me this time.

    Cheers,
    Rob

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