Will this work for you?
#ifdef __cplusplus
extern "C" { extern int Perl___notused(void); }
#else
extern int Perl___notused(void);
#endif
#define dNOOP extern int Perl___notused(void)
#define XSPROTO(name) void name(void)
#define XS(name) extern "C" XSPROTO(name)
void func1(void) {
dNOOP;
int i = Perl___notused();
}
XS(func2) {
dNOOP;
}
On May 4, 2012, at 11:59 AM, Craig A. Berry wrote:
>
> On May 4, 2012, at 11:57 AM, Craig A. Berry wrote:
>
>> I've been taking a swing at compiling Perl with the HP C++ compiler for
>> OpenVMS.[1] There are a number of wrinkles to iron out, one of which boils
>> down to:
>>
>> $ type try.c
>> #define dNOOP extern int Perl___notused(void)
>> #define XSPROTO(name) void name(void)
>> #define XS(name) extern "C" XSPROTO(name)
>>
>> void func1(void) {
>> dNOOP;
>> int i = Perl___notused();
>> }
>>
>> XS(func2) {
>> dNOOP;
>
> Bah, copy and paste error. There should be two more lines right here like so:
>
> int j = Perl___notused();
> }
>
>> $ cxx try.c
>>
>> dNOOP;
>> ..^
>> %CXX-E-INCLNKSPE, linkage specification is incompatible with previous
>> "Perl___notused" (declared at line 6)
>> at line number 11 in file D0:[craig.blead]TRY.C;30
>>
>> %CXX-I-MESSAGE, 1 error detected in the compilation of
>> "D0:[craig.blead]TRY.C;30".
>>
>> The macros in this test file have been patched together from what's in
>> XSUB.h and perl.h as seen when __cplusplus is defined. The dNOOP macro
>> means "don't do anything" and usually appears as an expansion of dVAR, which
>> means "don't do anything unless threads are enabled." For real-world
>> examples, look in mro.c, perlio.c, etc.
>>
>> What the compiler is whingeing about is that we've asked for two versions of
>> the external symbol "Perl___notused," one that is name mangled, and one
>> (because it's inside 'extern "C"' via the XS macro via the XSPROTO macro)
>> that is not mangled. And it's not just saying it's bad taste: it's throwing
>> an error, not a warning. Of course we don't *care* because "notused' means
>> we aren't going to use it, and are just faking so it looks like we're doing
>> something when we aren't, but the compiler doesn't know that.
>>
>> In my example I've inserted function calls to Perl___notused() so I can see
>> what symbol names the compiler is actually generating, but removing those
>> function calls (which corresponds more closely to the real-world build)
>> doesn't make the error go away.
>>
>> Other C++ compilers seem to silently create two different, unrelated symbols
>> from the same token without so much as a warning. For example, g++ clearly
>> shows us getting one mangled and one unmangled version of the symbol:
>>
>> % g++ -g -S -c try.c
>> % grep notused try.s
>> call __Z14Perl___notusedv
>> call _Perl___notused
>> .ascii "_Z14Perl___notusedv\0"
>> .ascii "Perl___notused\0
>>
>> I'm rather stumped about what to do. Any suggestions?
>>
>> [1] Getting the build to work with C++ has been on the to-do list for over
>> a decade. One of the developments in that time period is that on Itanium,
>> the backend for the C++ compiler is some gadget from Intel that is unrelated
>> to and purportedly generates much faster IA64 code than the traditional GEM
>> compiler backend for VMS that was ported from VAX to Alpha to IA64.
>> ________________________________________
>> Craig A. Berry
>> mailto:[email protected]
>>
>> "... getting out of a sonnet is much more
>> difficult than getting in."
>> Brad Leithauser
>>
>
> ________________________________________
> Craig A. Berry
> mailto:[email protected]
>
> "... getting out of a sonnet is much more
> difficult than getting in."
> Brad Leithauser
>
