C++/C mangleof inconsistency for OS X

[Michel Fortin via Digitalmars-d]

On 2015-04-21 17:01:51 +0000, Dan Olson <zans.is.for.cans at yahoo.com> said:

> Dan Olson <zans.is.for.cans at yahoo.com> writes:
> 
>> Jacob Carlborg <doob at me.com> writes:
>> 
>>> On 2015-04-20 18:33, Dan Olson wrote:
>>>> An observation on OSX w/ 2.067: mangleof for C++ (and D) names produces
>>>> the actual object file symbol while mangleof for C names strips a
>>>> leading underscore.
>>>> 
>>>> Is this intended?  If so what is rationale?
>>> 
>>> I don't think it's intentional. The point of "mangleof" is to evaluate
>>> to the actual mangled name, as it appears in the object file.
>> 
>> Thanks Jacob.
>> 
>> In that case, mangleof for extern(C) names on OS X and other systems
>> that add a leading underscore should include the underscore.
>> 
>> extern(C) int x;
>> version(linux) pragma(msg, foo.mangleof); // "x"
>> version(OSX) pragma(msg, foo.mangleof);   // "_x"
>> 
>> I'm trying to understand because ldc is different than dmd, and it is
>> related to proper debugging on systems with leading underscores.
>> pragma(mangle, name) is wrapped up in this too.  This needs to be right
>> to help D expand to other systems.
> 
> Hmmm, I can see another point of view where mangleof should produce the
> equivalent extern(C) symbol.  My gut says this is the way it should
> work.
> 
> If I want to call a C function void debug(const char*) from a C library,
> I would do this because of D "debug" keyword:
> 
>   pragma(mangle, "debug")
>   extern (C) void debug_c(const(char*));
> 
> Now I would think debug_c.mangleof -> "debug"
> (and that is indeed what dmd produces even on OS X).
> 
> On systems which prepend an underscore, we want compiler to take care of
> this so code is portable, otherwise code must do this:
> 
> version (OSX)
>   pragma(mangle, "_debug") extern (C) void debug_c(const(char*));
> else
>   pragma(mangle, "debug") extern (C) void debug_c(const(char*));

I think if you specify the mangling most of the time it's because you 
don't want the compiler to do it for you. But you should consider doing 
this:

string mangleC(string name) {
	version (OSX) return "_" ~ name;
	else return name;
}

pragma(mangle, mangleC("debug")) extern (C) void debug_c(const(char*));

-- 
Michel Fortin
michel.fortin at michelf.ca
http://michelf.ca