From @hakonhagland

I am trying to figure out the package name of the caller from an XSUB.
It turns out that Perl C API function caller_cx(0,NULL) does not return
package name of caller, the same way as Perl function caller() does. For
example​:

p.pl​:

#! /usr/bin/env perl
use lib './lib/My/blib/arch';
use lib './lib';
use My​::Caller;
My​::Caller​::test(); #XSUB
My​::Caller​::test2(); #Perl sub

lib/My/Caller.pm​:

package My​::Caller;
require Exporter;
require XSLoader;

our @​ISA = qw(Exporter);
our @​EXPORT_OK = qw( );
our @​EXPORT = qw( );
our $VERSION = '0.01';

XSLoader​::load();

sub test2 {
  my ( $package_name ) = caller;

  print "My​::Caller​::test2() : $package_name\n";
}
1;

lib/My/Caller.xs​:

#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"

void test() {
  const PERL_CONTEXT *cx = caller_cx(0, NULL);
  if ( cx != NULL ) {
  char *pack_name = HvNAME((HV*)CopSTASH(cx->blk_oldcop));
  printf( "My​::Caller​::test() : %s\n", pack_name );
  }
  else {
  printf( "My​::Caller​::test() : NULL\n" );
  }
}

MODULE = My​::Caller PACKAGE = My​::Caller
PROTOTYPES​: DISABLE

void
test ()
  PREINIT​:
  I32* temp;
  PPCODE​:
  temp = PL_markstack_ptr++;
  test();
  if (PL_markstack_ptr != temp) {
  PL_markstack_ptr = temp;
  XSRETURN_EMPTY;
  }
  return;

Output from running p.pl​:

My​::Caller​::test() : NULL
My​::Caller​::test2() : main

Expected output​:

My​::Caller​::test() : main
My​::Caller​::test2() : main

Running Perl version 5.24.1 on Ubuntu 16.10.

The whole test case can be downloaded form here​:

https://github.com/hakonhagland/caller_cx_bug

See also​:
http​://stackoverflow.com/q/42531519/2173773

Best regards,
Håkon Hægland

From @iabyn

On Thu, Mar 02, 2017 at 12​:14​:27PM -0800, Håkon Hægland wrote​:

I am trying to figure out the package name of the caller from an XSUB.
It turns out that Perl C API function caller_cx(0,NULL) does not return
package name of caller, the same way as Perl function caller() does. For
example​:

From the docs for caller_cx()​:

  Note that XSUBs don't get a stack frame, so C<caller_cx(0, NULL)> will
  return information for the immediately-surrounding Perl code

Since you are calling the XS function 'test' directly from the main
body of the script, it will return NULL. Wrapping the call in a function
will give the result you expect, e.g.

  sub f { My​::Caller​::test() }
  package Bar;
  :​:f();

gives

  My​::Caller​::test() : Bar

--
Modern art​:
  "That's easy, I could have done that!"
  "Ah, but you didn't!"

The RT System itself - Status changed from 'new' to 'open'

From @hakonhagland

Thanks Dave Mitchell! Wrapping the XSUB call in a Perl subroutine works
perfectly.

2017-03-06 13​:01 GMT+01​:00 Dave Mitchell via RT <perlbug-followup@​perl.org>​:

On Thu, Mar 02, 2017 at 12​:14​:27PM -0800, Håkon Hægland wrote​:

I am trying to figure out the package name of the caller from an XSUB.
It turns out that Perl C API function caller_cx(0,NULL) does not return
package name of caller, the same way as Perl function caller() does. For
example​:

From the docs for caller_cx()​:

Note that XSUBs don't get a stack frame\, so C\<caller\_cx\(0\, NULL\)> will
return information for the immediately\-surrounding Perl code

Since you are calling the XS function 'test' directly from the main
body of the script, it will return NULL. Wrapping the call in a function
will give the result you expect, e.g.

sub f \{ My​::Caller​::test\(\) \}
package Bar;
:​:f\(\);

gives

My​::Caller​::test\(\) : Bar

--
Modern art​:
"That's easy, I could have done that!"
"Ah, but you didn't!"

From @KES777

I think perl today should provide some thing like current context (and such structure already exists in the CORE)
Also there are already many things publically visible​:
@​current_context = __PACKAGE__ __FILE__ __LINE__ __SUB__ @​ARGV/@​_, $^H, $%H

And when sub is called perl just​: push @​stack, \@​current_context;

Today we should group all those things together

( Does API exists already? http​://stackoverflow.com/questions/42629915/is-there-a-way-to-access-special-tokens-in-perl-from-xs )

@iabyn - Status changed from 'open' to 'rejected'