Alignment exception on ARM in libvncclient zrle

[ghost]

Similar to issue #199 - Alignment exception on ARM in rfbWriteExact()

This code in zrle.c in libvncclient:

#if REALBPP!=BPP && defined(UNCOMP) && UNCOMP!=0
#if UNCOMP>0
#define UncompressCPixel(pointer) ((*(CARDBPP*)pointer)>>UNCOMP)
#else
#define UncompressCPixel(pointer) ((*(CARDBPP*)pointer)<<(-(UNCOMP)))
#endif
#else
#define UncompressCPixel(pointer) (*(CARDBPP*)pointer)
#endif

casts byte pointers to larger types without taking into consideration that some CPUs throw a bus error if the address is odd.

In my case, I'm only ever using 16bit colours (unsigned short) so I simply replaced the last define above with the following to fix the issue (for me):

#if BPP !=16
#define UncompressCPixel(pointer) (*(CARDBPP*)pointer)
#else
#define UncompressCPixel(pointer) ((pointer [1] << 8) | (pointer [0]))
#endif

If I ever move to 32 bit colours, I might fix it there too - but the device I've compiled my project for is 10 years old and will never use a different screen to what it has now. (iMX31 - in LE mode)

[bk138]

Is this with 0.9.12 or current master? 53073c8 changed somehting w.r.t. alignment.

[ghost]

Hi, it was a snapshot of the current master from about 4 weeks ago. Time flies, it took me almost that long to get it working on my old hardware. But work it does - it's very cool, thanks.

The commit mentioned above only addresses the issue in the VNCServer source which I'm not using, that file isn't in my project which is a VNCClient. It may well be the case that fixing it on the server side solves the problem on the client side, except I'm not connecting to a LibVNCServer server, I think it's RealVNC server that I've got (whatever comes as default/recommended for a Raspberry Pi).

Incidentally, I'm using the Arduino IDE (with a custom board profile for my device) to build my project. Arduino will compile the .ino and all .c / .cpp files in the project directory... Of course some of the .c files here are "do not compile" ones - so I renamed them as .h (well, except zlib.c which I named zlibc.h). I don't think I did much more (other than change some config settings for stuff I'm missing on my platform) so it might be worth thinking about making the filename change here... It would certainly remove any ambiguity and you can take out the warnings in the source to not compile? :)

[bk138]

As no one else was reporting this bug and the OP has turned into a 👻, I'll tentatively close this. Maybe 8f6b47d fixed it (altough it does not deal with alignment exceptions...)