Re: [rfa:solib] Handle start-address descriptors

[Andrew Cagney <ac131313 at redhat dot com>]

> Hello,
>
> The attached patch modifies the solib's computation of the exec's entry-point address so that it applies convert_from_func_ptr_addr() to the bfd start-address.  That way, when the bfd's start-address points at a descriptor, the true exec entry point is still obtained.
>
> Fixes ppc64's ability to debug shared libraries.

Attached is the patch as committed.  PPC64 GNU/Linux is now "useable".

Andrew

> PS: Ref
> http://sources.redhat.com/ml/gdb-patches/2003-10/msg00670.html

2003-10-31  Andrew Cagney  <cagney@redhat.com>

	* solib-svr4.c: Update copyright.  Include "bfd-target.h" and
	"exec.h".
	(exec_entry_point): New function.
	(enable_break): Create a "tmp_bfd_target", use that and
	entry_point_address when computing the relocation offset.
	(svr4_relocate_main_executable): Ditto with exec_bfd and exec_ops.
	* Makefile.in (solib-svr4.o): Update dependencies.

Index: Makefile.in
===================================================================
RCS file: /cvs/src/src/gdb/Makefile.in,v
retrieving revision 1.465
diff -u -r1.465 Makefile.in
--- Makefile.in	31 Oct 2003 19:19:51 -0000	1.465
+++ Makefile.in	31 Oct 2003 21:09:54 -0000
@@ -2298,7 +2298,8 @@
 	$(bcache_h) $(regcache_h)
 solib-svr4.o: solib-svr4.c $(defs_h) $(elf_external_h) $(elf_common_h) \
 	$(elf_mips_h) $(symtab_h) $(bfd_h) $(symfile_h) $(objfiles_h) \
-	$(gdbcore_h) $(target_h) $(inferior_h) $(solist_h) $(solib_svr4_h)
+	$(gdbcore_h) $(target_h) $(inferior_h) $(solist_h) $(solib_svr4_h) \
+	$(bfd_target_h) $(exec_h)
 sol-thread.o: sol-thread.c $(defs_h) $(gdbthread_h) $(target_h) \
 	$(inferior_h) $(gdb_stat_h) $(gdbcmd_h) $(gdbcore_h) $(regcache_h) \
 	$(symfile_h) $(gdb_string_h) $(gregset_h)
Index: solib-svr4.c
===================================================================
RCS file: /cvs/src/src/gdb/solib-svr4.c,v
retrieving revision 1.37
diff -u -r1.37 solib-svr4.c
--- solib-svr4.c	26 Aug 2003 23:35:19 -0000	1.37
+++ solib-svr4.c	31 Oct 2003 21:09:54 -0000
@@ -1,7 +1,7 @@
 /* Handle SVR4 shared libraries for GDB, the GNU Debugger.
-   Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000,
-   2001
-   Free Software Foundation, Inc.
+
+   Copyright 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999,
+   2000, 2001, 2003 Free Software Foundation, Inc.
 
    This file is part of GDB.
 
@@ -37,6 +37,9 @@
 #include "solist.h"
 #include "solib-svr4.h"
 
+#include "bfd-target.h"
+#include "exec.h"
+
 #ifndef SVR4_FETCH_LINK_MAP_OFFSETS
 #define SVR4_FETCH_LINK_MAP_OFFSETS() svr4_fetch_link_map_offsets ()
 #endif
@@ -911,6 +914,24 @@
 	  || in_plt_section (pc, NULL));
 }
 
+/* Given an executable's ABFD and target, compute the entry-point
+   address.  */
+
+static CORE_ADDR
+exec_entry_point (struct bfd *abfd, struct target_ops *targ)
+{
+  /* KevinB wrote ... for most targets, the address returned by
+     bfd_get_start_address() is the entry point for the start
+     function.  But, for some targets, bfd_get_start_address() returns
+     the address of a function descriptor from which the entry point
+     address may be extracted.  This address is extracted by
+     gdbarch_convert_from_func_ptr_addr().  The method
+     gdbarch_convert_from_func_ptr_addr() is the merely the identify
+     function for targets which don't use function descriptors.  */
+  return gdbarch_convert_from_func_ptr_addr (current_gdbarch,
+					     bfd_get_start_address (abfd),
+					     targ);
+}
 
 /*
 
@@ -984,6 +1005,7 @@
       int load_addr_found = 0;
       struct so_list *inferior_sos;
       bfd *tmp_bfd = NULL;
+      struct target_ops *tmp_bfd_target;
       int tmp_fd = -1;
       char *tmp_pathname = NULL;
       CORE_ADDR sym_addr = 0;
@@ -1019,6 +1041,11 @@
 	  goto bkpt_at_symbol;
 	}
 
+      /* Now convert the TMP_BFD into a target.  That way target, as
+         well as BFD operations can be used.  Note that closing the
+         target will also close the underlying bfd.  */
+      tmp_bfd_target = target_bfd_reopen (tmp_bfd);
+
       /* If the entry in _DYNAMIC for the dynamic linker has already
          been filled in, we can read its base address from there. */
       inferior_sos = svr4_current_sos ();
@@ -1042,7 +1069,8 @@
 	 the current pc (which should point at the entry point for the
 	 dynamic linker) and subtracting the offset of the entry point.  */
       if (!load_addr_found)
-	load_addr = read_pc () - tmp_bfd->start_address;
+	load_addr = (read_pc ()
+		     - exec_entry_point (tmp_bfd, tmp_bfd_target));
 
       /* Record the relocated start and end address of the dynamic linker
          text and plt section for svr4_in_dynsym_resolve_code.  */
@@ -1080,8 +1108,9 @@
 	    break;
 	}
 
-      /* We're done with the temporary bfd.  */
-      bfd_close (tmp_bfd);
+      /* We're done with both the temporary bfd and target.  Remember,
+         closing the target closes the underlying bfd.  */
+      target_close (tmp_bfd_target, 0);
 
       if (sym_addr != 0)
 	{
@@ -1200,7 +1229,7 @@
   interp_sect = bfd_get_section_by_name (exec_bfd, ".interp");
   if (interp_sect == NULL 
       && (bfd_get_file_flags (exec_bfd) & DYNAMIC) != 0
-      && bfd_get_start_address (exec_bfd) != pc)
+      && (exec_entry_point (exec_bfd, &exec_ops) != pc))
     {
       struct cleanup *old_chain;
       struct section_offsets *new_offsets;
@@ -1232,7 +1261,7 @@
 	 The same language also appears in Edition 4.0 of the System V
 	 ABI and is left unspecified in some of the earlier editions.  */
 
-      displacement = pc - bfd_get_start_address (exec_bfd);
+      displacement = pc - exec_entry_point (exec_bfd, &exec_ops);
       changed = 0;
 
       new_offsets = xcalloc (symfile_objfile->num_sections,