From @bulk88

I am not sure if you are proposing a new API or using INTERFACE_MACRO keyword as is.

If as is, not according to the docs which say

This keyword allows one to define an INTERFACE using a different way to extract a function pointer from an XSUB. The text which follows this keyword should give the name of macros which would extract/set a function pointer. The extractor macro is given return type, CV* , and XSANY.any_dptr for this CV* . The setter macro is given cv, and the function pointer.

The default value is XSINTERFACE_FUNC and XSINTERFACE_FUNC_SET . An INTERFACE keyword with an empty list of functions can be omitted if INTERFACE_MACRO keyword is used.

These seems to be written for C++/faux-C++ vtables, MS COM/OLE perhaps (see http://www.codeproject.com/Articles/14117/COM-in-plain-C-Part#premain4 where QueryInterface would be the offset into the vtable, the actual function pointer can never be stored in the CV * because each may/probably has a different QueryInterface func ptr), where the function pointer of what to call isn't store in CV's ANY member, but an offset into a table of function pointers, so the function pointers in the RW vtable can get swaped out after the CV is registered/newXSed. This does NOT affect how the function pointer is invoked, only how the CV's ANY member is converted to a function pointer.

XS_EUPXS(XS_Win32__Event_handleInBoolOut); /* prototype to pass -Wmissing-prototypes */
XS_EUPXS(XS_Win32__Event_handleInBoolOut)
{
dVAR; dXSARGS;
dXSFUNCTION(BOOL);
if (items != 1)
croak_xs_usage(cv, "event");
{
HANDLE event;
BOOL RETVAL;

{
SV * tsv = ST(0);
if (sv_derived_from(tsv, "Win32::Event")) {
IV tmp = SvIV((SV*)SvRV(tsv));
event = INT2PTR(HANDLE, tmp);
}
else
croak("event is not of type Win32::Event");
}
;
XSFUNCTION = XSINTERFACE_FUNC(BOOL,cv,XSANY.any_dptr);

RETVAL = XSFUNCTION(event);
ST(0) = boolSV(RETVAL);
}
XSRETURN(1);
}

After CPP.

static void XS_Win32__Event_handleInBoolOut(PerlInterpreter * my_perl, CV * cv);
static void
XS_Win32__Event_handleInBoolOut(PerlInterpreter * my_perl, CV * cv)
{
extern int Perl___notused(void);
SV **sp = (my_perl->Istack_sp);
I32 ax = (*(my_perl->Imarkstack_ptr)--);
SV **mark = (my_perl->Istack_base) + ax++;
I32 items = (I32) (sp - mark);
>>>>>>>>>>>>>>THIS WONT CHANGE<<<<<<<<<<<<<<<<<<<
BOOL(__stdcall * XSFUNCTION) ();
if (items != 1)
Perl_croak_xs_usage(cv, "event");
{
HANDLE event;
BOOL RETVAL;

{
SV *tsv = (my_perl->Istack_base)[ax + (0)];
if (Perl_sv_derived_from(my_perl, tsv, "Win32::Event")) {
IV tmp =
(((((SV *) ((tsv)->sv_u.svu_rv))->sv_flags & (0x00000100 | 0x00200000)) ==
0x00000100) ? ((XPVIV *) ((SV *) ((tsv)->sv_u.svu_rv))->sv_any)->xiv_u.
xivu_iv : Perl_sv_2iv_flags(my_perl, (SV *) ((tsv)->sv_u.svu_rv), 2));
event = (HANDLE) (tmp);
} else
Perl_croak_nocontext("event is not of type Win32::Event");
}
;
>>>>>>>>>>IF I USE INTERFACE_MACRO KEYWORD I'D CHANGE ONLY THE LINE DIRECTLY BELOW<<<<<<<<<<<
XSFUNCTION = ((BOOL(__stdcall *) ()) (((XPVCV *) ((void *) ((cv)->sv_any)))->xcv_start_u.xcv_xsubany.any_dptr));
>>>>>>>>>>>>>>THIS LINE BELOW WONT CHANGE<<<<<<<<<<<<<<<<<<<
RETVAL = XSFUNCTION(event);
(my_perl->Istack_base)[ax + (0)] = ((RETVAL) ? &(my_perl->Isv_yes) : &(my_perl->Isv_no));
}
do {
const IV tmpXSoff = (1);
(my_perl->Istack_sp) = (my_perl->Istack_base) + ax + (tmpXSoff - 1);
return;
} while (0);
}

Now lets look at macro for declaration of function pointer.

"dXSFUNCTION(BOOL);"

#define dXSFUNCTION(ret) XSINTERFACE_CVT(ret,XSFUNCTION)

XSINTERFACE_CVT(BOOL,XSFUNCTION);

#define XSINTERFACE_CVT(ret,name) ret (*name)()

BOOL (*XSFUNCTION)();

I tried your suggestion, it still crashed as c stack pointer corruption.

#define MYXSINTERFACE_FUNC(ret,cv,ptr) (ret(__stdcall *)())ptr
.....................
BOOL
handleInBoolOut(event)
HANDLE event
INTERFACE_MACRO:
MYXSINTERFACE_FUNC
XSINTERFACE_FUNC_SET
INTERFACE:
PulseEvent reset set

CPP output of above XS

static void XS_Win32__Event_handleInBoolOut(PerlInterpreter* my_perl , CV* cv);
static void XS_Win32__Event_handleInBoolOut(PerlInterpreter* my_perl , CV* cv)
{
extern int Perl___notused(void); SV **sp = (my_perl->Istack_sp); I32 ax = (*(my_perl->Imarkstack_ptr)--); SV **mark = (my_perl->Istack_base) + ax++; I32 items = (I32)(sp - mark);
>>>>>>>>>>>>>>>>no __stdcall here<<<<<<<<<<<<<<<<<<<<<
BOOL (*XSFUNCTION)();
if (items != 1)
Perl_croak_xs_usage(cv, "event");
{
HANDLE event;
BOOL RETVAL;

{
SV * tsv = (my_perl->Istack_base)[ax + (0)];
if (Perl_sv_derived_from(my_perl, tsv,"Win32::Event")) {
IV tmp = (((((SV*)((tsv)->sv_u.svu_rv))->sv_flags & (0x00000100|0x00200000)) == 0x00000100) ? ((XPVIV*) ((SV*)((tsv)->sv_u.svu_rv))->sv_any)->xiv_u.xivu_iv : Perl_sv_2iv_flags(my_perl, (SV*)((tsv)->sv_u.svu_rv),2));
event = (HANDLE)(tmp);
}
else
Perl_croak_nocontext("event is not of type Win32::Event");
}
;
XSFUNCTION = ((BOOL (*)())(((XPVCV*)((void *) ((cv)->sv_any)))->xcv_start_u.xcv_xsubany.any_dptr));

RETVAL = XSFUNCTION(event);
(my_perl->Istack_base)[ax + (0)] = ((RETVAL) ? &(my_perl->Isv_yes) : &(my_perl->Isv_no));
}
do { const IV tmpXSoff = (1); (my_perl->Istack_sp) = (my_perl->Istack_base) + ax + (tmpXSoff - 1); return; } while (0);
}

The result is a syntax error since the func ptrs are of different type.

lib\Win32\Event.c(293) : error C2440: '=' : cannot convert from 'BOOL (__stdcall
*)()' to 'BOOL (__cdecl *)()'

If you are talking about new API, are you suggesting adding 3rd line for INTERFACE_MACRO? Currently it only takes in 2 lines, here is the chunk from ParseXS.

sub INTERFACE_MACRO_handler {
my $self = shift;
$_ = shift;
my $in = $self->merge_section();

trim_whitespace($in);
if ($in =~ /\s/) { # two
($self->{interface_macro}, $self->{interface_macro_set}) = split ' ', $in;
}
else {
$self->{interface_macro} = $in;
$self->{interface_macro_set} = 'UNKNOWN_CVT'; # catch later
}
$self->{interface} = 1; # local
$self->{interfaces} = 1; # global
}

I also noticed like this the special interface macros are ignored with no warning.

BOOL
handleInBoolOut(event)
HANDLE event
INTERFACE:
PulseEvent reset set
INTERFACE_MACRO:
MYXSINTERFACE_FUNC
XSINTERFACE_FUNC_SET

but like this they take effect

BOOL
handleInBoolOut(event)
HANDLE event
INTERFACE_MACRO:
MYXSINTERFACE_FUNC
XSINTERFACE_FUNC_SET
INTERFACE:
PulseEvent reset set

I think that this 2nd bug is a very low priority over not supporting calling conventions

XS INTERFACE: token doesn't support calling conventions #14327

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