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digitalmars.D.learn - C++/D class interop example crashes

reply Jan <Jan Krassnigg.de> writes:
I just tried to get this example to work:
https://dlang.org/spec/cpp_interface.html#using_d_classes_from_cpp

It kept crashing for me with a 'privileged instruction' error 
when the function 'bar' was executed. Finally I removed the call 
to writefln and voilà it finally works.

So why does it fail? I assumed the standard library functions 
should all work.
I'm compiling with "dmd -shared -m64 -debug" and link against a 
C++ DLL that was built with VS2019. Should the D DLL not contain 
everything to be self-sufficient to use it's entire runtime 
functionality?
And if not, what other functions might be problematic?

Also, if anyone here has contacts to the people that maintain the 
samples, maybe someone should adjust the sample to not contain 
code that may break this way.
Mar 27 2021
parent reply Bastiaan Veelo <Bastiaan Veelo.net> writes:
On Saturday, 27 March 2021 at 15:09:20 UTC, Jan wrote:

 I just tried to get this example to work:
 https://dlang.org/spec/cpp_interface.html#using_d_classes_from_cpp

 It kept crashing for me with a 'privileged instruction' error 
 when the function 'bar' was executed. Finally I removed the 
 call to writefln and voilà it finally works.

 So why does it fail? I assumed the standard library functions 
 should all work.
 I'm compiling with "dmd -shared -m64 -debug" and link against a 
 C++ DLL that was built with VS2019. Should the D DLL not 
 contain everything to be self-sufficient to use it's entire 
 runtime functionality?
 And if not, what other functions might be problematic?


The example links objects statically. You may be experiencing 
additional challenges with crossing DLL boundaries. I have not 
yet used DLLs, but did you initialise the D runtime?

— Bastiaan.
Mar 27 2021
next sibling parent bachmeier <no spam.net> writes:
On Saturday, 27 March 2021 at 18:39:53 UTC, Bastiaan Veelo wrote:


 The example links objects statically. You may be experiencing 
 additional challenges with crossing DLL boundaries. I have not 
 yet used DLLs, but did you initialise the D runtime?

 — Bastiaan.


This is an example taken from the documentation. It should work 
out of the box.

I tried with LDC (don't have dmd on this computer) and I got this 
error:

/usr/bin/ld: base.o: undefined reference to symbol '_d_allocclass'
/usr/bin/ld: /usr/lib64/libdruntime-ldc-shared.so.90: error 
adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status

Given that someone interoperating with C++ probably cares about 
performance, it should also work out of the box with LDC, or at 
least tell you the changes that need to be made. I'll open an 
issue in the bug tracker when I return home (traveling now) if 
someone else doesn't.
Mar 27 2021
prev sibling parent reply Jan <Jan Krassnigg.de> writes:
On Saturday, 27 March 2021 at 18:39:53 UTC, Bastiaan Veelo wrote:

 The example links objects statically. You may be experiencing 
 additional challenges with crossing DLL boundaries. I have not 
 yet used DLLs, but did you initialise the D runtime?


I haven't done anything extra (I'm pretty new to D). Do you mean 
calling this from the D code before using writeln?
https://dlang.org/phobos/core_runtime.html#initialize

I would have thought that happens automatically anyway.
Mar 27 2021
parent Mike Parker <aldacron gmail.com> writes:
On Saturday, 27 March 2021 at 21:50:19 UTC, Jan wrote:

 On Saturday, 27 March 2021 at 18:39:53 UTC, Bastiaan Veelo 
 wrote:

 The example links objects statically. You may be experiencing 
 additional challenges with crossing DLL boundaries. I have not 
 yet used DLLs, but did you initialise the D runtime?


 I haven't done anything extra (I'm pretty new to D). Do you 
 mean calling this from the D code before using writeln?
 https://dlang.org/phobos/core_runtime.html#initialize

 I would have thought that happens automatically anyway.


It should be in this case since the D code in the example is an 
application with a D main. The compiler will generate an 
extern(C) main that initializes the runtime and calls your D 
main. You have to initialize the runtime manually in three cases: 
you implement an extern(C) main yourself, you use WinMain instead 
of main, or you implement a shared library in D.

The problem most likely has to do with your use of a DLL rather 
than linking statically as in the example. D interfaces with C 
DLLs just fine, but given that C++ compatibility is limited, I 
would expect issues when interfacing with C++ DLLs.
Mar 27 2021