I created a set of tests for this in lp:~pitti/qtubuntu-sensors/crash-
without-hw which reproduce the error. The actual crash happens in
platform-api's bridge.h:
#define IMPLEMENT_FUNCTION0(return_type, symbol) \
return_type symbol() \
{ \
static return_type (*f)() = NULL; \
DLSYM(&f, #symbol); \
return f();}
In this situation (desktop without hw sensors/Android) either the bridge
itself is NULL or the DLSYM returns NULL, in either case f ends up being
NULL and trying to call that will segfault; there is not a lot that
qtubuntu-sensors could do about that with the current API.
On the other hand, at this point platform-api does not really have a
good option for error handling: It could require that
IMPLEMENT_FUNCTION0 always returns a pointer and just return NULL on
failure, so that ua_sensors_accelerometer_new() will then return NULL as
expected if the sensor is not available. Or we add a new function to
platform-api that checks if the backend is available, and if that
returns false, qtubuntu-sensors will just avoid calling the ua_sensors_*
bits entirely. Personally I favour the first option, it's safe and
easier and avoids having to explicitly call this check function in
clients.
After that, qtubuntu-sensors still needs to be fixed to check the return
value for NULL as currently it just happily uses/calls this. It should
instead set the QtSensor-typical error state.
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https://bugs.launchpad.net/bugs/1272294
Title:
qtsensors crashes on desktop as there is no platform-api backend
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