Bug in the way that data is passed down to callback functions about go-yara

[plusvic]

This fix seems to work, but I'm not familiarized yet withcgo.

With that fixgo vet says: possible misuse of unsafe.Pointer because of the conversion of anuintptr back tounsafe.Pointer, but in this case I would say that's perfectly safe. The conversion is necessary only because yr_compiler_set_callback expects a void* for user_data and cgo translates it into unsafe.Pointer.

[hillu]

I have been able to reproduce the issue with Go 1.8.5 but not with Go 1.9.2 (Debian unstable/amd64). What version are you using?

My belief is that the garbage collector collects id right after it has been passed to C.compiler_set_callback.. Adding keepalive(id) at the end of the function seems to fix the issue here.

[plusvic]

I have Go 1.8 too.

Your belief makes sense. At first I thought that too, but then read that the GC doesn't free the object if you hold an unsafe.Pointer to it, and discarded the idea. What I didn't noticed is that the pointer is not hold by the function neither, so nothing prevents the GC from freeing id.

[plusvic]

BTW, what do you think about plusvic@7275017, I believe it's safe even if go vet complains, but I would like to hear a second opinion. I like it because you don't need to pass the address of id to the callback, you can pass id itself.

[hillu]

I have gone through a few iterations of trying to use integers / uintptr values where the Go compiler and/or runtime thought it was passing pointers around. It would work with the then-current compiler/runtime version but then the CGO rules (which are underdocumented anyway) would get changed and things would break.

At this point I have pretty much given up on that idea. Let's see if explicitly keeping the id values alive will do the trick...

[hillu]

Let's see what the Travis CI setup comes up with...

[hillu]

Woohoo, it crashed with every Go version but tip.

[hillu]

Ah well, it seems like the keepAlive function for go 1.6 also has a beneficial effect in this case. I am getting too old for this nonsense.