On Saturday, 23 February 2019 at 18:54:09 UTC, Thomas Mader wrote:
> I now know a little bit more. It fails at [1] and after the d_do_test.d object is created with:
>
> /private/var/folders/wq/m1dnr42s42n5msqk2v8l0lfc0000gn/T/nix-build-dmd-2.084.1.drv-49/dmd/generated/osx/release/64/dmd -conf= -m64 -fPIC -g -unittest -run tools/d_do_test.d
>
> the linking part in the newly created process with fork fails.

Yeah and I was so wrong about that.
Clearly the execution of the program failed ( https://github.com/dlang/dmd/blob/73fcf82ae1d6f0582c19e8c2ae0d09f319745521/src/dmd/link.d#L905 ) not the linking part.

The problem is that for whatever reason, Nix's clang does not add executable rights if the output file was already created without executable rights.

I created https://github.com/NixOS/nixpkgs/issues/57120 .