Re^2: SvPV Segmentation Fault

[adler187]

Ok, that worked:

./svpv.pl 
Starting Build Preprocess Stage                                       
+                                                                     
+                                                                     
+                             
Finished Build Preprocess Stage                                       
+                                                                     
+                                                                     
+                             
                                                                      
+                                                                     
+                                                                     
+                             
Starting Build Parse Stage
Finished Build Parse Stage

Starting Build Glue 1 Stage
Finished Build Glue 1 Stage

Starting Build Glue 2 Stage
Finished Build Glue 2 Stage

Starting Build Glue 3 Stage
Finished Build Glue 3 Stage

Starting Build Compile Stage
  Starting "perl Makefile.PL" Stage
Writing Makefile for _967160
Writing MYMETA.yml
  Finished "perl Makefile.PL" Stage

  Starting "make" Stage
/usr/bin/perl /usr/lib/perl5/5.14.2/ExtUtils/xsubpp  -typemap /usr/lib
+/perl5/5.14.2/ExtUtils/typemap   _967160.xs > _967160.xsc && mv _9671
+60.xsc _967160.c
cc -c  -I/home/kadler -D_REENTRANT -D_GNU_SOURCE -DPERL_USE_SAFE_PUTEN
+V -fno-strict-aliasing -pipe -fstack-protector -D_LARGEFILE_SOURCE -D
+_FILE_OFFSET_BITS=64 -fmessage-length=0 -O2 -Wall -D_FORTIFY_SOURCE=2
+ -fstack-protector -funwind-tables -fasynchronous-unwind-tables -g -W
+all -pipe   -DVERSION=\"0.00\" -DXS_VERSION=\"0.00\" -fPIC "-I/usr/li
+b/perl5/5.14.2/x86_64-linux-thread-multi/CORE"   _967160.c
Running Mkbootstrap for _967160 ()
chmod 644 _967160.bs
rm -f blib/arch/auto/_967160/_967160.so
cc  -shared -L/usr/local/lib64 -fstack-protector _967160.o  -o blib/ar
+ch/auto/_967160/_967160.so        \
        \
  
chmod 755 blib/arch/auto/_967160/_967160.so
cp _967160.bs blib/arch/auto/_967160/_967160.bs
chmod 644 blib/arch/auto/_967160/_967160.bs
  Finished "make" Stage

  Starting "make install" Stage
Files found in blib/arch: installing files in blib/lib into architectu
+re dependent library tree
Installing /home/kadler/_Inline/lib/auto/_967160/_967160.bs
Installing /home/kadler/_Inline/lib/auto/_967160/_967160.so
  Finished "make install" Stage

  Starting Cleaning Up Stage
  Finished Cleaning Up Stage

Finished Build Compile Stage

fred
1

But, I wasn't actually using Inline::C. Just using that as an example of using SvPV and SvPV_nolen to build my XS module. There must be something wrong with building my XS module, then.

I've been using perlxstut as a basis, specifically examples #4 and #5.

Here's mylib.c:

#include <stdlib.h>

#include "mylib.h"

PerlInterpreter *my_perl;

void foo(SV * sv)
{
    if(sv)
    {
        printf("%s\n", SvPV_nolen(sv));
    }
}

void bar(SV * sv)
{
    printf ("%i\n", SvPOK(sv));
}

Here's mylib.h:

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

#define TESTVAL 4
void foo(SV * sv);

void bar(SV * sv);

Here's Mytest2.xs:

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

#include "ppport.h"

#include "mylib/mylib.h"

#include "const-c.inc"

MODULE = Mytest2        PACKAGE = Mytest2        

INCLUDE: const-xs.inc

void foo(SV * sv)

void bar(SV * sv)

Everything else should be exactly as in perlxstut.

[dave_the_m]

PerlInterpreter *my_perl

That's very wrong. I don't know why you've put that there. You need to either pass the my_perl arg to the foo/bar functions using aTHX_/pTHX, or (less efficiently), retrieve it locally using dTHX.

Dave.

[adler187]

Hmm, was wondering about that. Initially I did not have the declaration, but then I got an error about 'my_perl' undeclared. I found some code online (that I didn't read thoroughly, I see) and declared the variable.

Apparently, that is not enough. Any good examples/tutorials on how to do this?

Or perhaps I'm taking the wrong approach here and there is a better way. Here's what I'm trying to do. I'm trying to write a function in C that can be called from perl that takes as input, basically argc and argv. It seems you can't actually pass an array of char * from perl, you need to handle an AV *. I'd like to keep all this code in the external library, instead of writing it in the XS file, but maybe I'm just making it harder for myself that way.

[dave_the_m]

See perlguts.pod for more details about the [adp]THX_? macros, but basically, you're using a perl compiled for multiplicility/threading, and in those perls, most perl functions (including SvPV()) expect to take an extra first argument, called my_perl, which is a pointer to the current perl interpreter.

The idea is that on threaded perls, these macros typically expand as follows:

aTHX   my_perl
aTHX_  my_perl,
pTHX   PerlInterpreter* my_perl
pTHX_  PerlInterpreter* my_perl,
dTHX   PerlInterpreter* my_perl =
           something_that_retrieves_the_current_perl();

while on unthreaded perls they expand to null strings.

You typically declare any function as expecting an interpreter as the first arg:

void foo(pTHX_ SV * sv) { ... }

and invoke it as

foo(aTHX_ some_sv);

Normally your XS sub will have been passed a my_perl arg, and you can pass this on down the chain of called subs using aTHX/pTHX. In those cases where this isn't possible, dTHX can be used within the declaration section of a function to recreate my_perl 'on the fly', but it's expensive:

void foo(SV * sv) {
    dTHX;
    ...
}

All the above assumes that PERL_NO_GET_CONTEXT is defined in your source. If it isn't then aTHX is redefined to directly compute the interpreter address, like dTHX. This means everything 'just works' without messing with aTHX/pTHX, but is slow. Since you were getting compilation errors about missing my_perl, I'm assuming you must have had PERL_NO_GET_CONTEXT defined.

Dave

[BrowserUk]

I'd start by looking for differences in the generated C files between the Inline::C and XS versions. Also, a comparison of the respective makefile.pl's might shed some light.