[erlang-questions] NIF+device problem moving R18->R19 / Mac 10.11->10.12

[Igor Clark]

Hi all,

I'm having problems updating a NIF to work correctly with R19 and/or 
MacOS Sierra (10.12). The NIF uses Mac OS C API calls to talk to some 
hardware. It's been working just fine with R18 on El Capitan, but it 
fails in a manner I don't understand when I trying to run it on R19 or 
Sierra. I'm pretty baffled as to what's going on, and wonder if any of 
the following might ring bells or set off a spider-sense for anyone here?

- The code continues to work 100% as expected on R18 / Mac OS El Capitan 
(10.11), as it has for the last year or so.

- On R19 on El Capitan, 99% of the C code works as before, but one 
particular MacOS C API call fails unexpectedly. It doesn't crash or 
cause errors directly, but it returns null instead of a valid value as 
before. There are no build errors or warnings. (I'm using 'pc' plugin 
version 1.5.0 with rebar3). Other MacOS API calls talking to the same 
hardware work as expected, sending correct commands, getting the 
hardware to carry out operations as expected and returning expected 
values, without any problems.

- On both R18 & R19 on Sierra, exactly the same problem occurs as above 
in R19 on El Capitan.

- If I make the failing/null-returning OS API call in a plain, 
simple-as-possible C file compiled with gcc (Apple LLVM/clang), it works 
as expected, *on both OS versions*.

- If I paste that same simple-as-possible C code verbatim into the NIF, 
as the first line in the load() function, and run it on R18/El Capitan, 
it continues to work as expected.

- If I then try to run that identical pasted-verbatim NIF code with no 
changes on R18/Sierra or on R19 & either OS version, this one particular 
function call fails, as above.

I realise it could be many things, and my initial thought was that it 
must be the OS change or even the hardware failing - but the hardware 
and C API call continue to work just fine on both OS versions when the 
NIF stuff is taken out of the picture, and on El Capitan, the 
previously-not-happening problem reliably (and only) starts happening 
when I switch from R18 to R19.

Did anything change between R18 and R19 that might somehow make some, 
but not all, external C function calls fail on El Capitan/clang 8.0.0? 
And could that be something that also makes the same thing happen on 
both R18 and R19 under Sierra/clang 8.1.0? Could it perhaps be something 
do with the port compiler & LD/CXX flags?

Any ideas as to where else I could look to try to track this down, or 
what might be causing this?

(BTW, I'm using homebrew erlang, and I've tried all the above with 
versions 18.1, 18.3, 19.0.2 and 19.3 on both OS versions. The gcc/clang 
version on El Capitan is from Xcode 8.1, "Apple LLVM version 8.0.0 
(clang-800.0.42.1)". On Sierra it's from Xcode 8.3.1, "Apple LLVM 
version 8.1.0 (clang-802.0.41)" - but as above, the plain/non-NIF C code 
works perfectly and identically on both versions.)

Thanks very much,
Igor