FlsFree not called, leading to crash

[levinli303]

FlsAlloc is called here, but we are not calling FlsFree when DLL is unloaded. This leads to crash that is mentioned here.

libobjc2/arc.mm

Line 57 in 0c1a893

return FlsAlloc(cleanupFunction);

I'm seeing this crash when objc.dll is used in a shell extension.

[davidchisnall]

Unloading dynamic libraries containing Objective-C is unsupported and will crash for a great many reasons, but this looks as if you're unloading objc.dll? That's definitely not supported and would require some significant changes to the library.

[levinli303]

Unloading dynamic libraries containing Objective-C is unsupported and will crash for a great many reasons, but this looks as if you're unloading objc.dll? That's definitely not supported and would require some significant changes to the library.

I don't have code to unload objc.dll. This might have come from explorer unloading my dll (it is a shell extension), and thus unloading the dlls that is no longer used. If that is the case, I could probably uninitialize the objc runtime when my dll is unloaded, but there does not seem to be a way to do that.

[davidchisnall]

No, because there is no good way of doing it. Pointers to internal library state flow everywhere and if we miss one then we introduce a security vulnerability. The risk in almost correctly supporting library unloading is far higher than the benefit from supporting it.