Crash when using closures on iOS+arm64

[Simon Frost <simon.frost@realvnc.com>]

Hi,

I’ve been attempting to use closures across 32-bit, 64-bit and simulator builds of an iOS project but I consistently see a crash on the arm64 build when the closure is executed. This can be reproduced in a stripped down Xcode project by simply copying the code from the “closure_simple.c” unit test into the iOS application’s main.m file. I’ve seen this issue on both the latest code from master and the v3.2.1 tagged release.

Specifically I see an EXC_BAD_ACCESS exception when trying to call the executable address pointer populated by ffi_closure_alloc. Somewhat interestingly I see that the executable address (out param) and the writeable address (return value) are set to the same value after calling ffi_closure_alloc on arm64, whereas they have different values on armv7. This may be a red herring though, as I also noticed they also have the same value when running in the i386 simulator where the code works correctly.

All other libffi functionality appears to work fine on arm64, the only issue appears to be calling closures. Can anyone shed any light on this, or give me any pointers as to how this could be resolved? Unfortunately I’m not well enough versed in the lower levels of libffi to look into fixing this myself.

Thanks in advance,
Simon