[Mono-devel-list] [patch]Patch DllNotFoundException triggered for missing unmanaged libraries

[Denis Gervalle]

I am probably loosing my time posting this patch, but for the case that 
all previous versions have been ignored by mistake, here my updated 
patch for beta3 that improve DllNotFoundException message when unmanaged 
library, dependancy of unmanaged library or function are missing.

For those who wonder why I have made this patch and have missed previous 
story, I append the story again here under.
Hope that this _last_ one will be considered for CVS check in. If any 
improvement is needed for ci, please ask!

Denis Gervalle
SOFTEC sa
http://www.softec.st

The old story :
We have written this patch (and enhance it latter) after seaching hard
in the dark why a dynamic library next to our mono assembly is
presumably not found (DllNotFoundException) by mono.
The attached patch (based on the beta release) modify the triggered
exception when MONO_DEBUG is defined to provide a larger error message
corresponding to the joined error message of all tries done using
g_module_open() (opposed to the actual situation which only report the 
last tried name). Here is a sample:

Unhandled Exception: System.DllNotFoundException: Trying libsample.so:
libsample.so: cannot open shared object file: No such file or directory
==> Trying ./libsample.so: ./libsample.so: cannot open shared object
file: No such file or directory ==> Trying sample.so:
libdependancy.so.0: cannot open shared object file: No such file or
directory

This patch also provide a detailled error report of missing entry points 
in unmanaged library using the same technique. Another sample:

Trying 'libsample.so': libsample.so: cannot open shared object file: No 
such file or directory ==> Trying ./libsample.so: Found ==> Searching 
function 'mysymbolA': 'mysymbolA': mono: undefined symbol: mysymbolA ==> 
Searching function 'mysymbol': 'mysymbol': mono: undefined symbol: mysymbol

This patch takes care of mint issues and mono pinvoke-wrapper issues.
For the latter, each exception messages are allocated permanently on the 
heap since the exception is triggered by the wrapper code for each call 
to a function from the missing library (and not during the loading
phase). This is why MONO_DEBUG is required to activate the code, since
it could "leak" memory if a lot of missing library are tried.
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