www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - Why export external(C) generate mangled names?

reply Suliman <evermind live.ru> writes:
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?
Oct 25 2019
next sibling parent Daniel Kozak <kozzi11 gmail.com> writes:
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
Oct 25 2019
prev sibling next sibling parent Daniel Kozak <kozzi11 gmail.com> writes:
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
Oct 25 2019
prev sibling next sibling parent Simen =?UTF-8?B?S2rDpnLDpXM=?= <simen.kjaras gmail.com> writes:
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
Oct 25 2019
prev sibling parent mipri <mipri minimaltype.com> writes:
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
Oct 25 2019