saveimage crash

[brage@…]

I have been experiencing the exact same bug as described in bug #1269, with
mapscript terminating in saveimage() while writing to sdout. The httpd process
give the warning "httpd in free(): error: modified (page-) pointer" and exits. 

After some debugging, i found that the problematic call is the call to gdFree()
in saveImage().

My setup has php loading both gd.so and php_mapscript.so at startup in
php/extensions.ini.

The problem seems to be a mismatch of gd versions. The php gd module compiles
its own version of libgd, and if the gd library is loaded before the mapscript
library, mapscript will use the php-spesific version. This should not be a
problem, except that the php version of gd.so doesn't export gdFree(). In the
php version of libgd, gdFree() is defined as a macro to efree(). The gdFree()
called by mapscript then belongs to the gd linked to mapscript and the
alloc-code used by msSaveImageBufferGD() and gdFree() does not match.

A workaround is to load the php_mapscript module before the gd module.

[dmorissette]

I don't think there is much we can do about this except reminding users that
they should not use the PHP bundled GD with PHP MapScript but instead they
should use a gd.so built with the same GD as PHP MapScript.

What do you suggest brage? Perhaps add something about this to the FAQ?

[brage@…]

Adding a note to the FAQ seems like a good idea. It should perhaps be noted that
it is only a problem if gd.so is dynamically loaded prior to mapscript.so.

I suspect I was lucky having BSD malloc issue a warning and killing the process,
I guess the effects might be more subtle on others systems.

[dmorissette]

Jeff: Do you want to take this one to add a FAQ?

[jmckenna@…]

ok.

[assefa]

I accidently set the bug target to FUTURE. ressetting to 4.10

[jmckenna]

I have added a note regarding this in the FAQ section of ​http://mapserver.gis.umn.edu/docs/howto/phpmapscript-install