How to emulate and call a call from XS?

Question

How to emulate sub behavior zin XSsub?

package XS;
sub hello {
    print "ARGS: >>@_<<\n";
    my $lvl;
    while( my @frame =  caller( $lvl++ ) ) {
        print ">>@frame[0..4]<<\n";
    }
}

sub z {
    &hello;
}

In my file .xsI have:

void
call_perl() {
    call_pv( "XS::hello", G_NOARGS );    
}

void
test(...)
    CODE:
        call_perl();

But the call XS::test(1,2,3)does not pass any arguments to hello.

Output:

ARGS: >><<
>>main -e 1 XS::hello <<

Here we see that the flag is $hasargsnot set because of the flag G_NOARG, but why @_is it cleared? What did I miss?

UPD
Seems to have found half the answer.

• G_NOARGS flag

  affects the creation of the @_ array for the Perl routine.

• When XSUBcalled perl, do not create a frame for it (do not remember where it is described) and do not fill in @_for it (it is described indirectly here )

  XSUB reference their stack arguments with the ST (x) macro

, :

XSUB PP?

: :

call_pv( "XS::hello", 0 );

PP. XSUB, XS::hello sub

int count =  call_pv( "XS::hello", 0 );
STAGAIN;
printf( "%s\n", SvPV_nolen( ST(0) ) );

, G_NOARGS, XSUB PP sub

Answer 1

XSUB (: ):

test(...)
CODE:
    AV *defav_old =  GvAV(PL_defgv);   # Save current @_

    AV *av = newAV();                  # Create new array
    av_extend(av, items -1);          
    AvREIFY_only(av);
    AvFILLp(av) =  items -1;
    Copy(MARK+1, AvARRAY(av), items, SV*); # Fill array by elements from stack

    GvAV(PL_defgv) =  av;     # point @_ to our new array


    PUSHMARK(SP);
    int count =  call_pv( "XS::Utils::hello", G_VOID | G_NOARGS );

    GvAV(PL_defgv) =  defav_old;  # Restore old @_