_MR_atomic_sub_int symbol not found on macOS

[poldy]

The full error message is:

dyld[47054]: symbol not found in flat namespace '_MR_atomic_sub_int'

I installed Mercury from homebrew using brew install mercury. This is on an M1 Mac running the latest Ventura. A sequential "hello world" program compiles and runs no problem. And indeed, when I compile the Dining Philosophers sample code with either --parallel or --grade hlc.par.gc it compiles ok, but when I run it gives the above error message.

[juliensf]

I assume that you are using clang as the C compiler here. The problem is simply that there is not a definition of MR_atomic_sub_int for clang on Aarch64 based systems in the runtime; we will need to add one.
(There is a generic definition for GCC which should work on M1 based systems, although I've not tested that myself,
so installing GCC via homebrew and using that may be an option.)

[poldy]

Yes, I'm using clang.

I added the bare minimum of <stdatomic.h> code to get the build to complete. It could be quite a lot of work, but there are some nice features that Mercury could make use of if you introduced a minimum required version of C11.

[juliensf]

Requiring the use of C11 is not an option in the short to medium term. MSVC only just gained some initial experimental support for C11/C17 style atomics (and I gather even that is not complete). It would make sense for us to starting C11
atomics on platforms where they are supported (i.e. in preference to the inline assembly).

[poldy]

I logged PR #114 in an attempt to do this. Feel free to review ...