Re^2: How to setup the DynaLoader in a dynamically loaded perl?

Thanks for your helpful suggestions. Your example compiles and runs, but:

$ ldd aaa
        linux-vdso.so.1 (0x00007ffd0e4c6000)
        libperl.so.5.30 => /lib64/libperl.so.5.30 (0x00007fe9264b5000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fe926493000)
        libdl.so.2 => /lib64/libdl.so.2 (0x00007fe92648c000)
        libc.so.6 => /lib64/libc.so.6 (0x00007fe9262c3000)
        libm.so.6 => /lib64/libm.so.6 (0x00007fe92617d000)
        libcrypt.so.2 => /lib64/libcrypt.so.2 (0x00007fe926142000)
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So it is already linked to the perl shared library. If I remove -lperl from the link arguments I get:

in function `xs_init':
/home/jv/tmp/aaa.c:28: undefined reference to `PL_thr_key'
/bin/ld: /home/jv/tmp/aaa.c:28: undefined reference to `pthread_getspe
+cific'
/bin/ld: /home/jv/tmp/aaa.c:28: undefined reference to `Perl_newXS'
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EDIT: Managed to get it going by adding a Perl_newXS function as follows:

CV* Perl_newXS(pTHX_ const char *name, XSUBADDR_t subaddr, const char 
+*filename) {
  CV* (*imp)(tTHX, const char*, XSUBADDR_t, const char*);
  imp = (CV* (*)(tTHX, const char*, XSUBADDR_t, const char*)) dlsym( h
+andle, "Perl_newXS" );
  return (*imp)(my_perl, name, subaddr, filename);
}
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The complete proof-of-concept program is now:

#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <EXTERN.h>
#include <perl.h>

void *handle;            /* for dl */

static PerlInterpreter *my_perl;

void (*boot_DynaLoader)(pTHX_ CV* cv);

CV* Perl_newXS(pTHX_ const char *name, XSUBADDR_t subaddr, const char 
+*filename) {
  CV* (*imp)(tTHX, const char*, XSUBADDR_t, const char*);
  imp = (CV* (*)(tTHX, const char*, XSUBADDR_t, const char*)) dlsym( h
+andle, "Perl_newXS" );
  return (*imp)(my_perl, name, subaddr, filename);
}

void xs_init(pTHX) {
    static const char file[] = __FILE__;
    dXSUB_SYS;
    PERL_UNUSED_CONTEXT;
    newXS( "DynaLoader::boot_DynaLoader", boot_DynaLoader, file );
}

int main( int argc, char **argv, char **env ) {
  /* open shared lib */
  handle = dlopen("perl530.so", RTLD_LAZY);
  if ( !handle ) {
    fprintf( stderr, "%s\n", dlerror() );
    exit(EXIT_FAILURE);
  }

  /* Get entry point for perl_alloc */
  void* (*perl_alloc)();
  perl_alloc = (void*(*)()) dlsym(handle, "perl_alloc");
  /* Call perl_alloc */
  my_perl = (*perl_alloc)();

  /* perl_construct */
  void (*perl_construct)(void*);
  perl_construct = (void(*)(void*)) dlsym(handle, "perl_construct");
  (*perl_construct)(my_perl);

  /* boot_DynaLoader */
  boot_DynaLoader = (void (*)(pTHX_ CV* cv)) dlsym(handle, "boot_DynaL
+oader");
 
  /* perl_parse */
  void (*perl_parse)(void*, void*, int, char**, char**);
  perl_parse = (void(*)(void*, void*, int, char**, char**)) dlsym(hand
+le, "perl_parse");
  (*perl_parse)(my_perl, xs_init, argc, argv, env);

  /* perl_run */
  int (*perl_run)(void*);
  perl_run = (int(*)(void*)) dlsym(handle, "perl_run");
  int result = (*perl_run)(my_perl);

  /* perl_destruct */
  void(*perl_destruct)(void*);
  perl_destruct = (void(*)(void*)) dlsym(handle, "perl_destruct");
  (*perl_destruct)(my_perl);

  /* perl_free */
  void(*perl_free)(void*);
  perl_free = (void(*)(void*)) dlsym(handle, "perl_free");
  (*perl_free)(my_perl);

  return result;
}
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Build with: $(perl -MConfig -e 'print $Config{cc}') p.c $(perl -MExtUtils::Embed -e ccopts ) -o aaa -ldl -Wl,--rpath=. Although it seems that dynamic loading is not yet functional... For example, this fails:

aaa -MFcntl=:flock -E "say 1+LOCK_NB"
Undefined subroutine &Fcntl::LOCK_NB called at -e line 1.
[download]

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Re^3: How to setup the DynaLoader in a dynamically loaded perl?
by bliako (Monsignor) on May 05, 2020 at 21:06 UTC

As I said, you will need to dlsym anything that you may use later.

However, when I did this:

CV* (*Perl_newXS)(pTHX_ const char *name, XSUBADDR_t subaddr, const ch
+ar *filename);

....
Perl_newXS = (CV* (*)(pTHX_ const char *name, XSUBADDR_t subaddr, cons
+t char *filename) )dlsym(handle, "Perl_newXS");
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I got

 error: ‘Perl_newXS’ redeclared as different kind of symbol
/usr/lib64/perl5/CORE/proto.h:2517:19: note: previous declaration of ‘
+Perl_newXS’ was here
 2517 | PERL_CALLCONV CV* Perl_newXS(pTHX_ const char *name, XSUBADDR_
+t subaddr, const char *filename);
[download]

So, that's a neat trick you have there! (though I would make imp static)

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