Re: dlopening the C runtime library

[Paolo Bonzini]

> > Right. dlsym(RTLD_NEXT, "open") will give you the one that you shadowed;
> > this might not be the real symbol yet as there may be other wrappers
> > loaded, and it might not be the one from libc as applications are
> > allowed to provide their own definitions of symbols and have them take
> > precedence.
>
> That looks like what I'm looking for. I don't seem to find an analogous
> flag for lt_dlsym, in libtool's documentation, so I'll go with native
> dlsym, then.

RTLD_NEXT seems like a better choice, but just in case I am using the 
following Autoconf stuff:

m4/libc-so-name.m4:
dnl Sets the variables LIBC_SO_NAME and LIBC_SO_DIR to the directory
dnl and basename for the C library.
AC_DEFUN([GST_LIBC_SO_NAME],
[AC_CACHE_CHECK([how to dlopen the C library], gst_cv_libc_so_name, [
  if test $GCC = yes; then
    gst_lib_path=`$CC --print-multi-os-directory $CFLAGS $CPPFLAGS`
    case $gst_lib_path in
      .) gst_lib_path= ;;
      *) gst_lib_path=$gst_lib_path/ ;;
    esac
  else
    gst_lib_path=
  fi
  case $gst_lib_path in
    /*) gst_libc_search_path="${gst_lib_path}libc.so*
          ${gst_lib_path}libc-*.so
          ${gst_lib_path}libc.sl
          ${gst_lib_path}libSystem.dylib" ;;
    *) gst_libc_search_path="/shlib/libc.so \
        /lib/${gst_lib_path}libc.so* \
        /usr/lib/${gst_lib_path}libc.so.* \
        /usr/lib/${gst_lib_path}libc.sl \
        /lib/${gst_lib_path}libc-*.so \
        /System/Library/Frameworks/System.framework/System \
        /usr/lib/libSystem.dylib"
  esac

  gst_lib_sysroot=`$CC --print-sysroot`
  for i in $gst_libc_search_path; do
    if test -f "$gst_lib_sysroot$i"; then
      oldwd=`pwd`
      gst_cv_libc_so_name=`basename $i`
      gst_cv_libc_so_dir=`dirname $i`
      cd "$gst_cv_libc_so_dir" && gst_cv_libc_so_dir=`pwd`
      cd $oldwd
      break
    fi
  done])
LIBC_SO_NAME=$gst_cv_libc_so_name
LIBC_SO_DIR=$gst_cv_libc_so_dir
AC_SUBST(LIBC_SO_NAME)
AC_SUBST(LIBC_SO_DIR)
])

libc.la.in:
# libc.la - a libtool library file
# Generated by GNU libtool
# Created for GNU Smalltalk's dynamic loading mechanism.

# The name that we can dlopen(3).
dlname='@LIBC_SO_NAME@'

# Names of this library.
library_names='@LIBC_SO_NAME@'

# Libraries that this one depends upon.
dependency_libs=''

# Is this an already installed library?
installed=yes

# Directory that this library needs to be installed in:
libdir='@LIBC_SO_DIR@'

in configure.ac:
GST_LIBC_SO_NAME
AC_CONFIG_FILES([libc.la])