Re: C++ aliases in <netdb.h>

[Pedro Alves]

On 12/18/2016 01:16 AM, Bruno Haible wrote:
> Pedro Alves wrote:
>> m4/inet_pton.m4 has this:
>>
>>     if test $ac_cv_have_decl_inet_pton = yes; then
>>       dnl It needs to be overridden, because the stdcall calling convention
>>       dnl is not compliant with POSIX.
>>       REPLACE_INET_PTON=1
>>       INET_PTON_LIB="-lws2_32"
>>     else
>>       HAVE_DECL_INET_PTON=0
>>       HAVE_INET_PTON=0
>>     fi
>>   else
>>
>>
>> Given the "stdcall calling convention is not compliant with POSIX",
>> I wonder whether the right fix would be to somehow cause those
>> functions to be replaced too?
> 
> From the point of C programs, replacing 'getaddrinfo' and 'freeaddrinfo'
> is overkill, IMO. Most programs just call these functions the way they are
> declared in the .h file, through direct call, not through function pointers.
> 
> I just added some similar replacements for <math.h> functions that are defined
> as inline functions by MSVC. The justification is that <math.h> functions are
> occasionally called through function pointers (e.g. you can imagine a 'plot'
> function, an 'integrate' function, etc. that takes a float->float function
> as a pointer).
> 
> From the point of C++ programs:
>   - if you get an error in the .h file, from the _GL_CXXALIAS_SYS or
>     _GL_CXXALIASWARN invocation for example, or for GNULIB_NAMESPACE,
>     it's worth providing the replacement.
>   - if you only get an error in a SIGNATURE_CHECK, it's probably not worth it.
>     Just conditionalize the the SIGNATURE_CHECK then.
>     But if you want to provide the fix through REPLACE_xxx=1, I won't stop 
> you.

I agree that full replacement for to handle calling convention
is overkill.  

A simpler trampoline stdcall -> cdecl stub/trampoline inline replacement
like the "operator()" one I suggested earlier would be better for these
cases.  But even better, I think would be to handle C as well.  

I.e., for the case where the system function does not really need
replacement as it works properly, but needs calling convention wrapping,
generate an adapter/trampoline cdecl replacement like:

 inline rettype rpl_func parameters
 {
   return func arguments;
 }

and then the C++ wrapper would call rpl_func instead of ::func,
and for C you get the usual '#define func rpl_func'.

But again, this would require tweaking the _GL_CXXALIAS_SYS
macro to pass down the "arguments" list, maybe give it a different
name, _GL_CXXALIAS_SYS_ARGS or some such, and adjusting
all affected _GL_CXXALIAS_SYS calls.

TBC, I'm not planning on proposing a patch.

Thanks,
Pedro Alves