[RFC/ia64] link against libunwind rather than using dlopen

[Joel Brobecker <brobecker at adacore dot com>]

Hello,

This is something that I mentioned back in Aug 2005, and which came back
to bite me a little. Basically, on ia64 hosts, we dlopen libunwind rather
that link GDB against it.

This has two consequences:

  - I cannot link libunwind statically, which is very important
    in my case;

  - But also, I was trying to figure out why Steve Elcey, at HP,
    was having trouble when he's using GDB on ia64-hpux. I thought
    I had reproduced the problem, and it took 30min of debugging
    to realize that the libunwind had not been initialized, due
    to a problem during the dlopen.   The real problem is that this
    failure was completely silent, so there was no way to know
    without debugging that this had happened.

This patch is a first step towards treating libunwind the same way
we treat the other libraries such as expat, iconv, etc. What it does
is change the configury perform a link check against libunwind.
The --with-libunwind option is also extended to allow a path to
be given, when libunwind is installed at a non-standard location.

There are a few adjustements that are needed after that, mostly:
  - Some macros no longer exists, but we can use HAVE_LIBUNWIND
    for that purpose;
  - We set the various function pointers directly, rather than
    doing a dlsym.

This is not the whole series yet, as I want to make sure that we're
still OK with this approach before I waste more time on this.  Next
on the list is to delete the libunwind_load phase, and use the unw_*
symbols directly (so all the function unw_*_p pointers will disappear).

gdb/ChangeLog:

        * configure.ac: Allow the argument of the --with-libunwind
        option to be the prefix where libunwind is installed.
        Perform a link check against libunwind, rather than
        a couple of header file checks.
        * configure, config.in: Regenerate.
        * ia64-tdep.c: Replace uses of HAVE_LIBUNWIND_IA64_H by
        HAVE_LIBUNWIND.
        * libunwind-frame.h: Replace HAVE_LIBUNWIND_H by HAVE_LIBUNWIND.
        * libunwind-frame.c: Remove dlfcn.h include.
        (libunwind_load): Reimplement without using dlopen.

What do you guys think?

Thanks,
-- 
Joel

---
 gdb/config.in         |    6 ---
 gdb/configure         |  107 ++++++++++++++++++++++++++++++++++---------------
 gdb/configure.ac      |   49 +++++++++++++++++-----
 gdb/ia64-tdep.c       |   10 ++--
 gdb/libunwind-frame.c |   59 +++++----------------------
 gdb/libunwind-frame.h |    4 +-
 6 files changed, 128 insertions(+), 107 deletions(-)

diff --git a/gdb/configure.ac b/gdb/configure.ac
index 8c12a44..d2e3792 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -304,20 +304,45 @@ esac
 
 # Libunwind support.
 AC_ARG_WITH(libunwind,
-AS_HELP_STRING([--with-libunwind], [use libunwind frame unwinding support]),
-[case "${withval}" in
-  yes)  enable_libunwind=yes ;;
-  no)   enable_libunwind=no ;;
-  *)    AC_MSG_ERROR(bad value ${withval} for GDB with-libunwind option) ;;
-esac],[
-  AC_CHECK_HEADERS(libunwind.h libunwind-ia64.h)
-  if test x"$ac_cv_header_libunwind_h" = xyes -a x"$ac_cv_header_libunwind_ia64_h" = xyes; then
-    enable_libunwind=yes;
-  fi
+  AS_HELP_STRING([--with-libunwind@<:@=LIBUNWIND@:>@],
+                 [use libunwind frame unwinding support (auto/yes/no/libunwind-path)]),
+  [], [with_libunwind=auto])
+
+AC_DEFUN([AC_CHECK_LIBUNWIND],
+[
+  save_LIBS=$LIBS
+  LIBS="$LIBS -lunwind-ia64 -lunwind"
+  case "$host_os" in
+    hpux*) # On this platform, libunwind depends on libuca...
+           LIBS="$LIBS -luca"
+           ;;
+  esac
+  AC_LINK_IFELSE(AC_LANG_PROGRAM([#include "libunwind.h"],
+                                 [unw_init_local (0, 0);]),
+                 [enable_libunwind=yes],
+                 [enable_libunwind=no
+                  LIBS=$save_LIBS])
 ])
-   
+
+if test "$with_libunwind" = "no"; then
+  AC_MSG_WARN([libunwind support disabled; some features may be unavailable.])
+  enable_libunwind=no
+else
+  case "$with_libunwind" in
+    auto|yes) AC_CHECK_LIBUNWIND()
+          ;;
+    *)    # The argument is the prefix where libunwind has been installed.
+          CPPFLAGS="$CPPFLAGS -I${with_libunwind}/include"
+          LIBS="$LIBS -L${with_libunwind}/lib"
+          AC_CHECK_LIBUNWIND()
+          ;;
+  esac
+  if test "$with_libunwind" != "auto" -a "$enable_libunwind" != "yes"; then
+    AC_MSG_ERROR(libunwind library is missing.)
+  fi
+fi
+
 if test x"$enable_libunwind" = xyes; then
-  AC_CHECK_HEADERS(libunwind.h libunwind-ia64.h)
   AC_DEFINE(HAVE_LIBUNWIND, 1, [Define if libunwind library is being used.])
   CONFIG_OBS="$CONFIG_OBS libunwind-frame.o"
   CONFIG_DEPS="$CONFIG_DEPS libunwind-frame.o"
diff --git a/gdb/config.in b/gdb/config.in
index c1d7c68..7f8d41c 100644
--- a/gdb/config.in
+++ b/gdb/config.in
@@ -236,12 +236,6 @@
 /* Define if libunwind library is being used. */
 #undef HAVE_LIBUNWIND
 
-/* Define to 1 if you have the <libunwind.h> header file. */
-#undef HAVE_LIBUNWIND_H
-
-/* Define to 1 if you have the <libunwind-ia64.h> header file. */
-#undef HAVE_LIBUNWIND_IA64_H
-
 /* Define to 1 if you have the `w' library (-lw). */
 #undef HAVE_LIBW
 
diff --git a/gdb/configure b/gdb/configure
[snip'ed]
diff --git a/gdb/ia64-tdep.c b/gdb/ia64-tdep.c
index 68e5021..0090e38 100644
--- a/gdb/ia64-tdep.c
+++ b/gdb/ia64-tdep.c
@@ -41,7 +41,7 @@
 #include "ia64-tdep.h"
 #include "cp-abi.h"
 
-#ifdef HAVE_LIBUNWIND_IA64_H
+#ifdef HAVE_LIBUNWIND
 #include "elf/ia64.h"           /* for PT_IA_64_UNWIND value */
 #include "libunwind-frame.h"
 #include "libunwind-ia64.h"
@@ -942,7 +942,7 @@ ia64_pseudo_register_read (struct gdbarch *gdbarch, struct regcache *regcache,
 
   if (regnum >= V32_REGNUM && regnum <= V127_REGNUM)
     {
-#ifdef HAVE_LIBUNWIND_IA64_H
+#ifdef HAVE_LIBUNWIND
       /* First try and use the libunwind special reg accessor,
 	 otherwise fallback to standard logic.  */
       if (!libunwind_is_initialized ()
@@ -2392,7 +2392,7 @@ static const struct frame_base ia64_frame_base =
   ia64_frame_base_address
 };
 
-#ifdef HAVE_LIBUNWIND_IA64_H
+#ifdef HAVE_LIBUNWIND
 
 struct ia64_unwind_table_entry
   {
@@ -3189,7 +3189,7 @@ static struct libunwind_descr ia64_libunwind_descr =
   &ia64_unw_rse_accessors,
 };
 
-#endif /* HAVE_LIBUNWIND_IA64_H  */
+#endif /* HAVE_LIBUNWIND  */
 
 static int
 ia64_use_struct_convention (struct type *type)
@@ -4031,7 +4031,7 @@ ia64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_dummy_id (gdbarch, ia64_dummy_id);
 
   set_gdbarch_unwind_pc (gdbarch, ia64_unwind_pc);
-#ifdef HAVE_LIBUNWIND_IA64_H
+#ifdef HAVE_LIBUNWIND
   frame_unwind_append_unwinder (gdbarch,
                                 &ia64_libunwind_sigtramp_frame_unwind);
   frame_unwind_append_unwinder (gdbarch, &ia64_libunwind_frame_unwind);
diff --git a/gdb/libunwind-frame.c b/gdb/libunwind-frame.c
index 677d4c5..eacd4ff 100644
--- a/gdb/libunwind-frame.c
+++ b/gdb/libunwind-frame.c
@@ -32,8 +32,6 @@
 #include "objfiles.h"
 #include "regcache.h"
 
-#include <dlfcn.h>
-
 #include "gdb_assert.h"
 #include "gdb_string.h"
 
@@ -505,54 +503,17 @@ libunwind_get_reg_special (struct gdbarch *gdbarch, struct regcache *regcache,
 static int
 libunwind_load (void)
 {
-  void *handle;
-
-  handle = dlopen (LIBUNWIND_SO, RTLD_NOW);
-  if (handle == NULL)
-    return 0;
-
-  /* Initialize pointers to the dynamic library functions we will use.  */
-
-  unw_get_reg_p = dlsym (handle, get_reg_name);
-  if (unw_get_reg_p == NULL)
-    return 0;
-
-  unw_get_fpreg_p = dlsym (handle, get_fpreg_name);
-  if (unw_get_fpreg_p == NULL)
-    return 0;
-
-  unw_get_saveloc_p = dlsym (handle, get_saveloc_name);
-  if (unw_get_saveloc_p == NULL)
-    return 0;
-
-  unw_is_signal_frame_p = dlsym (handle, is_signal_frame_name);
-  if (unw_is_signal_frame_p == NULL)
-    return 0;
+  unw_get_reg_p = UNW_OBJ(get_reg);
+  unw_get_fpreg_p = UNW_OBJ(get_fpreg);
+  unw_get_saveloc_p = UNW_OBJ(get_save_loc);
+  unw_is_signal_frame_p = UNW_OBJ(is_signal_frame);
+  unw_step_p = UNW_OBJ(step);
+  unw_init_remote_p = UNW_OBJ(init_remote);
+  unw_create_addr_space_p = UNW_OBJ(create_addr_space);
+  unw_destroy_addr_space_p = UNW_OBJ (destroy_addr_space);
+  unw_search_unwind_table_p = UNW_OBJ(search_unwind_table);
+  unw_find_dyn_list_p = UNW_OBJ(find_dyn_list);
 
-  unw_step_p = dlsym (handle, step_name);
-  if (unw_step_p == NULL)
-    return 0;
-
-  unw_init_remote_p = dlsym (handle, init_remote_name);
-  if (unw_init_remote_p == NULL)
-    return 0;
-
-  unw_create_addr_space_p = dlsym (handle, create_addr_space_name);
-  if (unw_create_addr_space_p == NULL)
-    return 0;
-
-  unw_destroy_addr_space_p = dlsym (handle, destroy_addr_space_name);
-  if (unw_destroy_addr_space_p == NULL)
-    return 0;
-
-  unw_search_unwind_table_p = dlsym (handle, search_unwind_table_name);
-  if (unw_search_unwind_table_p == NULL)
-    return 0;
-
-  unw_find_dyn_list_p = dlsym (handle, find_dyn_list_name);
-  if (unw_find_dyn_list_p == NULL)
-    return 0;
-   
   return 1;
 }
 
diff --git a/gdb/libunwind-frame.h b/gdb/libunwind-frame.h
index 9b88f71..b4c3a4c 100644
--- a/gdb/libunwind-frame.h
+++ b/gdb/libunwind-frame.h
@@ -20,7 +20,7 @@
    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
 
-#ifdef HAVE_LIBUNWIND_H
+#ifdef HAVE_LIBUNWIND
 
 struct frame_info;
 struct frame_id;
@@ -74,4 +74,4 @@ int libunwind_get_reg_special (struct gdbarch *gdbarch,
 
 #endif /* libunwind-frame.h */
 
-#endif /* HAVE_LIBUNWIND_H  */
+#endif /* HAVE_LIBUNWIND  */
-- 
1.7.0.4