I thought that export extern(C) is needed for C compatibility. But When I am compiling follow code

export extern(C)
{
    void foo()
    {
    }
}

I am getting section that have mangled names:

� foo.d �  �7nO �  �
CV �,  FLAT_TEXTCODE_DATADATACONST_BSSBSS �	 �    
 �	 i    
 �	 i   
 �	 i    	
 �  � _foo �
  �  � _foo  � FMBFMFME �	 �    
 �	 �   
 �	 �

 � 
__D3foo12__ModuleInfoZ      �
          

� �           foo  �
          � � 
 �

Why is __D3foo12__ModuleInfoZ added to obj file?

On Fri, Oct 25, 2019 at 12:35 PM Suliman via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
>
> I thought that export extern(C) is needed for C compatibility.
> But When I am compiling follow code
>
> export extern(C)
> {
>      void foo()
>      {
>      }
> }
>
> I am getting section that have mangled names:
>
> �   foo.d �   �7nO �   � CV �,
>  FLAT _TEXT CODE _DATA DATA CONST _BSS BSS �     �        �      i
>     �    i        �      i        �    �   _foo �
>    �   �   _foo  �   FMB FM FME �        �        �      �       �       �
>    �     __D3foo12__ModuleInfoZ      �
>
> � �               foo  �
>             �  �     �
>
> Why is __D3foo12__ModuleInfoZ added to obj file?

Try to compile with -betterC

On Fri, Oct 25, 2019 at 12:56 PM Daniel Kozak <kozzi11@gmail.com> wrote:
>
> On Fri, Oct 25, 2019 at 12:35 PM Suliman via Digitalmars-d <digitalmars-d@puremagic.com> wrote:
> >
> > I thought that export extern(C) is needed for C compatibility.
> > But When I am compiling follow code
> >
> > export extern(C)
> > {
> >      void foo()
> >      {
> >      }
> > }
> >
> > I am getting section that have mangled names:
> >
> > �   foo.d �   �7nO �   � CV �,
> >  FLAT _TEXT CODE _DATA DATA CONST _BSS BSS �     �        �      i
> >     �    i        �      i        �    �   _foo �
> >    �   �   _foo  �   FMB FM FME �        �        �      �       �       �
> >    �     __D3foo12__ModuleInfoZ      �
> >
> > � �               foo  �
> >             �  �     �
> >
> > Why is __D3foo12__ModuleInfoZ added to obj file?
>
> Try to compile with -betterC

You should get:

[kozak@missandei ~]$ dmd -c -ofobj.o obj.d
[kozak@missandei ~]$ nm obj.o
0000000000000000 t
                 U _d_dso_registry
0000000000000000 R _D3obj12__ModuleInfoZ
0000000000000000 W foo
                 U __start_minfo
                 U __stop_minfo

[kozak@missandei ~]$ dmd -betterC -c -ofobj.o obj.d
[kozak@missandei ~]$ nm obj.o
0000000000000000 t
0000000000000000 W foo

On Friday, 25 October 2019 at 10:31:15 UTC, Suliman wrote:
> I thought that export extern(C) is needed for C compatibility. But When I am compiling follow code
>
> export extern(C)
> {
>     void foo()
>     {
>     }
> }
>
> I am getting section that have mangled names:
>
> � foo.d �  �7nO �  �
CV �,  FLAT_TEXTCODE_DATADATACONST_BSSBSS �	 �    
 �	 i    
 �	 i   
 �	 i    	
 �  � _foo �
>   �  � _foo  � FMBFMFME �	 �    
 �	 �   
 �	 �
> 
 � 
__D3foo12__ModuleInfoZ      �
>           

> � �           foo  �
>           � � 
 �
>
> Why is __D3foo12__ModuleInfoZ added to obj file?


Is your module (source file) called foo? Because that name is for the ModuleInfo of a module by that name, and has nothing to do with the function called the same.

Like Daniel said, -betterc inhibits the creation of moduleinfo, so if that's what you're after, you should use it.

--
  Simen

On Friday, 25 October 2019 at 10:31:15 UTC, Suliman wrote:
> I thought that export extern(C) is needed for C compatibility.

This is only the case for toplevel functions. If there's any nesting,
you still get D mangling but you get C calling conventions.

> But When I am compiling follow code
>
> export extern(C)
> {
>     void foo()
>     {
>     }
> }

There's no mangling with this code for me. I have to add a struct {}
around it to see mangling.

>
> I am getting section that have mangled names:
>

Look with: objdump -dwr --no-show-raw-insn <filename>

You'll get output like

  000000000042d5f8 <foo>:
    42d5f8:	push   %rbp
    42d5f9:	mov    %rsp,%rbp
    42d5fc:	pop    %rbp
    42d5fd:	retq
  	...

  000000000042d600 <_D4x1244test3barMUZv>:
    42d600:	push   %rbp
    42d601:	mov    %rsp,%rbp
    42d604:	pop    %rbp
    42d605:	retq

for

  extern(C) void foo() {}

  struct test {
      export extern(C) {
          void bar() {}
      }
  }

A note about this was added to the documentation with

https://github.com/dlang/dlang.org/pull/1911/files

but it might be easy to miss since it's not in InterfaceToC