Versioning a symbol in libpthread.

["Carlos O'Donell" <carlos at systemhalted dot org>]

Roland,

I have some questions about versioning symbols in libpthread.  From
the recipe given below, I did not expect to have to do step #5
(manually version pthread_mutex_init). Could you review the process
and comment on step #5 please? I would have expected the Versions file
to version pthread_mutex_init at GLIBC_2.9.

1. Create a Versions file

Versions
~~~
libc {
  GLIBC_2.9 {
    pthread_mutex_init;
  }
}

libpthread {
  GLIBC_2.9 {
    pthread_mutex_init;
    # protected?
    __pthread_mutex_init;
  }
}
~~~
Notes: Why is __pthread_mutex_init in the Versions list? I would have
expected this to be the local default used internally by libpthread.
This appears to be something historical.

2. Define old version of structures in machine dependent internaltypes.h

3. Create the old version of the library function e.g.

old_pthread_mutex_init.c
~~~
/* snip */
#include <errno.h>
#include "pthreadP.h"
#include <shlib-compat.h>

#if SHLIB_COMPAT(libpthread, GLIBC_2_0, GLIBC_2_9)
int
__pthread_mutex_init_hppa_2_0 (pthread_mutex_hppa_2_0_t *var,
                                 const pthread_mutexattr_t *attr)
{
  compat_init(var);
  compat_malloc(var);
  return __pthread_mutex_init(var->compat, attr);
}
compat_symbol (libpthread, __pthread_mutex_init_hppa_2_0, pthread_mutex_init,
               GLIBC_2_0);
#endif
~~~

4. Make copies of foward.c, init.c and pthreadP.h, all required to
update the forwarding stubs in libc.
Notes: ports  nptl/init.c will be used by csu/init.c, therefore rename
csu/init.c to csu/csu-init.c and fixup csu/Makefile.

forward.c:
~~~
/* snip */
#if SHLIB_COMPAT(libc, GLIBC_2_0, GLIBC_2_9)
FORWARD2 (__pthread_mutex_init_hppa_2_0, int attribute_compat_text_section,
         (pthread_mutex_hppa_2_0_t *mutex, const pthread_mutexattr_t
*mutexattr),
         (mutex, mutexattr), return 0)
compat_symbol (libc, __pthread_mutex_init_hppa_2_0, pthread_mutex_init,
               GLIBC_2_0);
#endif
FORWARD (pthread_mutex_init,
         (pthread_mutex_t *mutex, const pthread_mutexattr_t *mutexattr),
         (mutex, mutexattr), 0)
versioned_symbol (libc, __pthread_mutex_init, pthread_mutex_init,
                  GLIBC_2_9);
/* snip */
~~~

init.c
~~~
/* snip */
    .ptr_pthread_mutex_init = INTUSE(__pthread_mutex_init),
# if SHLIB_COMPAT(libpthread, GLIBC_2_0, GLIBC_2_9)
    .ptr___pthread_mutex_init_hppa_2_0 = __pthread_mutex_init_hppa_2_0,
# endif
/* snip */
~~~

pthreadP.h
~~~
/* snip */
extern int __pthread_mutex_init (pthread_mutex_t *__mutex,
                                 __const pthread_mutexattr_t *__mutexattr);
extern int __pthread_mutex_init_hppa_2_0 (pthread_mutex_hppa_2_0_t *__mutex,
                                 __const pthread_mutexattr_t *__mutexattr);
/* snip */
~~~

5. Version __pthread_mutex_init.

~~~
/* snip */
#ifndef INCLUDED_SELF
# define INCLUDED_SELF
# include <pthread_mutex_init.c>
#else
# include <shlib-compat.h>
# include <libc-symbols.h>
# include "pthreadP.h"
# undef strong_alias
# define strong_alias(name, aliasname)
# include_next <pthread_mutex_init.c>
# undef strong_alias
# define strong_alias(name, aliasname) _strong_alias(name, aliasname)
versioned_symbol (libpthread, __pthread_mutex_init,
                  pthread_mutex_init, GLIBC_2_9);
INTDEF(__pthread_mutex_init)
#endif
~~~

With step #5 libpthread contains:
~~~
 eu-readelf -a nptl/libpthread.so.0 | grep pthread_mutex_init
  0x0001cf08  PARISC_IPLT     0x00009ac8      +0 __pthread_mutex_init
  115: 00009ac8    540 FUNC    GLOBAL DEFAULT       11
__pthread_mutex_init@@GLIBC_2.2
  232: 00009ac8    540 FUNC    GLOBAL DEFAULT       11
pthread_mutex_init@@GLIBC_2.9
  233: 00017560    260 FUNC    GLOBAL DEFAULT       11
pthread_mutex_init@GLIBC_2.2
  270: 00009ac8    540 FUNC    LOCAL  HIDDEN        11
__pthread_mutex_init_internal
  355: 00017560    260 FUNC    LOCAL  DEFAULT       11
__pthread_mutex_init_hppa_2_0
  451: 00009ac8    540 FUNC    GLOBAL DEFAULT       11 __pthread_mutex_init
  530: 00009ac8    540 FUNC    GLOBAL DEFAULT       11
pthread_mutex_init@@GLIBC_2.9
  603: 00017560    260 FUNC    GLOBAL DEFAULT       11
pthread_mutex_init@GLIBC_2.2
~~~
Which correctly has pthread_mutex_init@@GLIBC_2.9. However I did not
expect __pthread_mutex_init@@GLIBC_2.2, but this is likely becuase the
underscored symbol isn't versioned and falls into the default minimum
symbol set.

*Without* step #5 libpthread contains:
~~~
eu-readelf -a libpthread.so.0 | grep pthread_mutex_init
  0x0001cee4  PARISC_IPLT     0x00009aa8      +0 __pthread_mutex_init
  115: 00009aa8    540 FUNC    GLOBAL DEFAULT       11
__pthread_mutex_init@@GLIBC_2.2
  232: 00017540    260 FUNC    GLOBAL DEFAULT       11
pthread_mutex_init@GLIBC_2.2
  181: 00009aa8    540 FUNC    LOCAL  DEFAULT       11 pthread_mutex_init
  271: 00009aa8    540 FUNC    LOCAL  HIDDEN        11
__pthread_mutex_init_internal
  356: 00017540    260 FUNC    LOCAL  DEFAULT       11
__pthread_mutex_init_hppa_2_0
  452: 00009aa8    540 FUNC    GLOBAL DEFAULT       11 __pthread_mutex_init
  603: 00017540    260 FUNC    GLOBAL DEFAULT       11
pthread_mutex_init@GLIBC_2.2
~~~
Which is missing a global default pthread_mutex_init@@GLIBC_2.9, or
even a pthread_mutex_init with global default visibility.

Cheers,
Carlos.