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dmd -run fails with Nix on macOS Mojave
Feb 20
sarn
February 19
On macOS Mojave dmd built with Nix can not be used with the -run parameter.

dmd -run hello.d
/var/tmp/dmd_runNVSCJp: Permission denied
core.thread.ThreadError@core/thread.d(3206): Unable to load thread state

A normal compile and run works and it used to work before I upgraded to Mojave.
I checked the official dmd binary for macOS and everything works there.
It seems to be a problem with Nix in connection with Mojave.

I came here to ask for hints.

It's dmd 2.084.1 and the line number of the ThreadError is not right. I don't know why.

I don't know what the compiler wants to write to /var/tmp/dmd_runNVSCJp and why that fails with a Permission denied.
February 19
On Tuesday, 19 February 2019 at 20:32:32 UTC, Thomas Mader wrote:
> I don't know what the compiler wants to write to /var/tmp/dmd_runNVSCJp and why that fails with a Permission denied.

Ok I found it, it's created in link.d
February 19
On Tuesday, 19 February 2019 at 20:37:48 UTC, Thomas Mader wrote:
> On Tuesday, 19 February 2019 at 20:32:32 UTC, Thomas Mader wrote:
>> I don't know what the compiler wants to write to /var/tmp/dmd_runNVSCJp and why that fails with a Permission denied.
>
> Ok I found it, it's created in link.d

Not sure if macos does this, but on linux you can mount directories as "noexec" which means you can't run executables that live inside those mounts.  On linux you could check this with "mount | grep /var/tmp", not sure if it's the same on MacOS.

(Related Issue: https://github.com/dragon-lang/rund/issues/17)
February 19
On Tuesday, 19 February 2019 at 21:06:29 UTC, Jonathan Marler wrote:
> On Tuesday, 19 February 2019 at 20:37:48 UTC, Thomas Mader wrote:
>> On Tuesday, 19 February 2019 at 20:32:32 UTC, Thomas Mader wrote:
>>> I don't know what the compiler wants to write to /var/tmp/dmd_runNVSCJp and why that fails with a Permission denied.
>>
>> Ok I found it, it's created in link.d
>
> Not sure if macos does this, but on linux you can mount directories as "noexec" which means you can't run executables that live inside those mounts.  On linux you could check this with "mount | grep /var/tmp", not sure if it's the same on MacOS.
>
> (Related Issue: https://github.com/dragon-lang/rund/issues/17)

No that's not the problem.
Nix does not change mounts when a binary is run. All it's doing is specify it's own directories and this also includes the System Libs of macOS.
That's also the reason why official dmd package still works as all Nix stuff is contained in one directory and is only used by Nix executables.
Probably it's something with the C environment.
With this I could explain the thread error but the permission denied leaves me clueless because the directory is clearly writable.
I also already tried to patch link.d so P_tmpdir is not used anymore but a custom dir I defined but it did not change anything.
February 19
On Tuesday, 19 February 2019 at 21:27:19 UTC, Thomas Mader wrote:
> On Tuesday, 19 February 2019 at 21:06:29 UTC, Jonathan Marler wrote:
>> On Tuesday, 19 February 2019 at 20:37:48 UTC, Thomas Mader wrote:
>>> On Tuesday, 19 February 2019 at 20:32:32 UTC, Thomas Mader wrote:
>>>> I don't know what the compiler wants to write to /var/tmp/dmd_runNVSCJp and why that fails with a Permission denied.
>>>
>>> Ok I found it, it's created in link.d
>>
>> Not sure if macos does this, but on linux you can mount directories as "noexec" which means you can't run executables that live inside those mounts.  On linux you could check this with "mount | grep /var/tmp", not sure if it's the same on MacOS.
>>
>> (Related Issue: https://github.com/dragon-lang/rund/issues/17)
>
> No that's not the problem.
> Nix does not change mounts when a binary is run. All it's doing is specify it's own directories and this also includes the System Libs of macOS.

Yes I'm pretty familair with how Nix works.  I'm not talking about Nix changing mount settings or installing files in places it shouldn't, I'm talking about where dmd stores the executable its going to run.  Of course I don't know if this is the issue you're running into, but if it is then it's not necessarily a problem with Nix, it could just be a configuration issue with DMD as to where it store temporary executables.


February 19
On Tuesday, 19 February 2019 at 21:34:30 UTC, Jonathan Marler wrote:
> Yes I'm pretty familair with how Nix works.  I'm not talking about Nix changing mount settings or installing files in places it shouldn't, I'm talking about where dmd stores the executable its going to run.  Of course I don't know if this is the issue you're running into, but if it is then it's not necessarily a problem with Nix, it could just be a configuration issue with DMD as to where it store temporary executables.

I ruled out that idea by now because:

- I changed dmd to use a tmpdir I created in the home dir of the running user and I got the same error.

- If the temporary file can not be created I think that dmd should output a dedicated error message: https://github.com/dlang/dmd/blob/6151bf8bfb21416b5857a64ab7fd8ae318ca02fb/src/dmd/link.d#L464

- The ThreadError seems to be connected to fork and the call to fork comes after the creation of the file in runLINK

I never tried to debug dmd with a debugger but I think it's time to start.
February 19
On Tuesday, 19 February 2019 at 22:07:58 UTC, Thomas Mader wrote:
> On Tuesday, 19 February 2019 at 21:34:30 UTC, Jonathan Marler wrote:
>> [...]
>
> I ruled out that idea by now because:
>
> - I changed dmd to use a tmpdir I created in the home dir of the running user and I got the same error.
>
> - If the temporary file can not be created I think that dmd should output a dedicated error message: https://github.com/dlang/dmd/blob/6151bf8bfb21416b5857a64ab7fd8ae318ca02fb/src/dmd/link.d#L464
>
> - The ThreadError seems to be connected to fork and the call to fork comes after the creation of the file in runLINK
>
> I never tried to debug dmd with a debugger but I think it's time to start.

Not sure if Mac has an equivalent to "strace", but if it does than that's a really easy first step.  See which system call actually failed and get the error code.
February 20
On Tuesday, 19 February 2019 at 23:05:22 UTC, Jonathan Marler wrote:
> Not sure if Mac has an equivalent to "strace", but if it does than that's a really easy first step.  See which system call actually failed and get the error code.

Mac OS X has DTrace instead of strace.
https://8thlight.com/blog/colin-jones/2015/11/06/dtrace-even-better-than-strace-for-osx.html

(+1 to syscall tracing being faster than a debugger for this kind of problem.)
February 22
On 2019-02-19 21:32, Thomas Mader wrote:
> On macOS Mojave dmd built with Nix can not be used with the -run parameter.
> 
> dmd -run hello.d
> /var/tmp/dmd_runNVSCJp: Permission denied
> core.thread.ThreadError@core/thread.d(3206): Unable to load thread state
>
> I don't know what the compiler wants to write to /var/tmp/dmd_runNVSCJp and why that fails with a Permission denied.

I had the same issue on FreeBSD (TrueOS actually), because it's /tmp is mounted as "noexec". But that's usually not the case on macOS.

-- 
/Jacob Carlborg
February 23
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. This is the linking command:

clang++ d_do_test.o -o /var/tmp/dmd_runNGJfCU -g -m64 -Xlinker -no_compact_unwind -L../../phobos/generated/osx/release/64 -lphobos2 -lpthread -lm

The file /var/tmp/dmd_runNGJfCU is created with rw permissions for my user.

If I replace the "childpid = fork();" line with "childpid = 0;" it works.
So there seems to be something wrong with the permissions of the child process.

[1] https://github.com/dlang/dmd/blob/73fcf82ae1d6f0582c19e8c2ae0d09f319745521/src/dmd/link.d#L692
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