Re: The emacs_backtrace "feature"

[Juri Linkov <juri@jurta.org>]

>>  . Many calls to emacs_backtrace in the current sources limit the
>>    number of backtrace frames to 10, but that is an arbitrary
>>    limitation which will be too small in most, if not all, situations.
>
> We can change that number if needed.  10 was enough for my use
> cases.  Of course no number will be ideal in all cases.  Still, 10
> is almost invariably better than 0.

10 is too small number.  I tried to visit an .ico file, and Emacs crashed
in the ImageMagick library.  I found the backtrace in ~/.xsession-errors:

Backtrace:
/usr/local/src/emacs/trunk/src/emacs[0x4f1bdb]
/usr/local/src/emacs/trunk/src/emacs[0x4d70dd]
/usr/local/src/emacs/trunk/src/emacs[0x4f1b4e]
/usr/local/src/emacs/trunk/src/emacs[0x4f28c3]
/lib/libpthread.so.0(+0xfb40)[0x7fa162357b40]
/lib/libc.so.6(gsignal+0x35)[0x7fa16136eba5]
/lib/libc.so.6(abort+0x180)[0x7fa1613726b0]
/lib/libc.so.6(__assert_fail+0xf1)[0x7fa161367a71]
/usr/lib/libMagickCore.so.3(DestroyLinkedList+0xea)[0x7fa1628939ba]
/usr/lib/libMagickCore.so.3(DestroyExceptionInfo+0x52)[0x7fa16287bdc2]
/usr/lib/libMagickWand.so.3(DestroyPixelWand+0x5b)[0x7fa162cee84b]
...

Running it through `addr2line' helps to see source-code lines of
crash-processing functions:

emacs_backtrace at /usr/local/src/emacs/trunk/src/sysdep.c:2034
terminate_due_to_signal at /usr/local/src/emacs/trunk/src/emacs.c:314
handle_fatal_signal at /usr/local/src/emacs/trunk/src/sysdep.c:1552
deliver_thread_signal at /usr/local/src/emacs/trunk/src/sysdep.c:1537
 (inlined by) deliver_fatal_thread_signal at /usr/local/src/emacs/trunk/src/sysdep.c:1564

But the most interesting part of the backtrace with information
about Emacs image functions is truncated.

Displaying more lines might help to understand whether the bug is caused
by the old version of ImageMagick or by a bug in src/image.c.

Would be better to increase the number of lines to 24 or 32
or any other round number.