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:craigbe...@mac.com
>
> "... getting out of a sonnet is much more
> difficult than getting in."
> Brad Leithauser
>
________________________________________
Craig A. Berry
mailto:craigbe...@mac.com
"... getting out of a sonnet is much more
difficult than getting in."
Brad Leithauser
