XS generation error, function returning list

Cacadril has asked for the wisdom of the Perl Monks concerning the following question:

Following the perlxstut, in example 5 I get the following error:

   Mytest.c:251:2: error: too few arguments to function 'statfs'
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The example creates a module function statfs that is tested like this in t/Mytest.t:

my @a;
@a = &Mytest::my_statfs("/blech"); # Test non-existent file/directory
ok( scalar(@a) == 1 && $a[0] == 2 );
@a = &Mytest::my_statfs("/");      # Test existing file/directory
is ( scalar(@a), 7 );
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In other words, the function returns a list.

In Mytest.xs:

#include <sys/vfs.h>
    ...
void
statfs(path)
        char * path
    INIT:
        int i;
        struct statfs buf;

    PCODE:
        i = statfs(path, &buf);
        if (i == 0) {
                XPUSHs(sv_2mortal(newSVnv(buf.f_bavail)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_bfree)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_blocks)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_bsize)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_ffree)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_files)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_type)));
        } else {
                XPUSHs(sv_2mortal(newSVnv(errno)));
        }
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The Makefile.PL generates the following C code:

XS_EUPXS(XS_Mytest_statfs)
{
    dVAR; dXSARGS;
    if (items != 1)
       croak_xs_usage(cv,  "path");
    {
        char *  path = (char *)SvPV_nolen(ST(0))
;
#line 43 "Mytest.xs"
        int i;
        struct statfs buf;

    PCODE:
        i = statfs(path, &buf);
        if (i == 0) {
                XPUSHs(sv_2mortal(newSVnv(buf.f_bavail)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_bfree)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_blocks)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_bsize)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_ffree)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_files)));
                XPUSHs(sv_2mortal(newSVnv(buf.f_type)));
        } else {
                XPUSHs(sv_2mortal(newSVnv(errno)));
        }
#line 250 "Mytest.c"

        statfs(path);
    }
    XSRETURN_EMPTY;
}
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Look near the end of this function. Why is this call to statfs being generated? I have tried to call the module function "my_statfs" instead of "statfs", Then the call near the end of the function becomes my_statfs(buf), while the call to the actual library function statfs remains statfs(path, buf), and the compiler message becomes "undefined reference to `my_statfs'".

Why is this call being generated? What am I doing wrong?

And, is XSRETURN_EMPTY the appropriate macro for a function that returns a non-empty list?

Comment on XS generation error, function returning list Select or Download Code

Replies are listed 'Best First'.
Re: XS generation error, function returning list by Corion (Patriarch) on Jul 21, 2016 at 19:49 UTC
The section name should be `PPCODE:`, with two P's instead of `PCODE:` as you wrote. I think that Perl/xsubpp leaves `PCODE:` alone and the C compiler interprets this as a label instead of a special XS section.	[reply] [d/l] [select]
Re^2: XS generation error, function returning list by Cacadril (Novice) on Jul 21, 2016 at 22:37 UTC
Confirmed, thanks. I should have written PPCODE with two P's. Now it compiles. The generated C code is now `PUTBACK; return;` at the position of the PPCODE. I can only speculate that the generated call "statfs(buf)" at the end of the function has some cause related to the fact that with the PCODE being interpreted as a label, all the code was in the INIT secion.	[reply] [d/l]