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Handle fork exit more gracefully in linux-fork.c


A cleanup I made while working on my next patch.  I was debugging
some checkpoint.exp failures by hand, and the most obvious thing for
me to do was to create a checkpoint, let the current one exit, and
then continue the previous checkpoint - but as soon as I did this
it crashed with corrupted register state.

We weren't restoring the saved registers in linux_fork_mourn_inferior.
And we were somehow clobbering the previous registers.  Moving
some bits from the explicit context-switch code into the restore-a-fork
routine fixed all that.

Look OK?

-- 
Daniel Jacobowitz
CodeSourcery

2006-02-27  Daniel Jacobowitz  <dan@codesourcery.com>

	* linux-fork.c: Include "gdb_assert.h".
	(fork_load_infrun_state): Set inferior_ptid and stop_pc here.
	Update the register cache and selected frame also.
	(linux_fork_mourn_inferior): Use fork_load_infrun_state.  Return
	to single fork mode if necessary.
	(linux_fork_context): Remove bits handled by fork_load_infrun_state.
	* Makefile.in (linux_fork_h): New.
	(linux-fork.o, linux-nat.o): Update.

Index: src/gdb/linux-fork.c
===================================================================
--- src.orig/gdb/linux-fork.c	2006-02-27 10:59:47.000000000 -0500
+++ src/gdb/linux-fork.c	2006-02-27 11:10:45.000000000 -0500
@@ -24,6 +24,7 @@
 #include "regcache.h"
 #include "gdbcmd.h"
 #include "infcall.h"
+#include "gdb_assert.h"
 #include "gdb_string.h"
 #include "linux-fork.h"
 
@@ -239,9 +240,19 @@ fork_load_infrun_state (struct fork_info
   extern void nullify_last_target_wait_ptid ();
   int i;
 
+  inferior_ptid = fp->ptid;
+
   if (fp->savedregs && fp->clobber_regs)
     regcache_cpy (current_regcache, fp->savedregs);
 
+  registers_changed ();
+  reinit_frame_cache ();
+
+  /* We must select a new frame before making any inferior calls to
+     avoid warnings.  */
+  select_frame (get_current_frame ());
+
+  stop_pc = read_pc ();
   nullify_last_target_wait_ptid ();
 
   /* Now restore the file positions of open file descriptors.  */
@@ -354,12 +365,19 @@ linux_fork_mourn_inferior (void)
      We need to delete that one from the fork_list, and switch
      to the next available fork.  */
   delete_fork (inferior_ptid);
-  if (fork_list)	/* Paranoia, shouldn't happen.  */
-    {
-      inferior_ptid = fork_list[0].ptid;
-      printf_filtered (_("[Switching to %s]\n"), 
-		       target_pid_to_str (inferior_ptid));
-    }
+
+  /* There should still be a fork - if there's only one left,
+     delete_fork won't remove it, because we haven't updated
+     inferior_ptid yet.  */
+  gdb_assert (fork_list);
+
+  fork_load_infrun_state (fork_list);
+  printf_filtered (_("[Switching to %s]\n"),
+		   target_pid_to_str (inferior_ptid));
+
+  /* If there's only one fork, switch back to non-fork mode.  */
+  if (fork_list->next == NULL)
+    delete_fork (inferior_ptid);
 }
 
 /* Fork list <-> user interface.  */
@@ -555,17 +573,10 @@ linux_fork_context (struct fork_info *ne
     error (_("No such fork/process"));
 
   if (!oldfp)
-    {
-      oldfp = add_fork (ptid_get_pid (inferior_ptid));
-    }
+    oldfp = add_fork (ptid_get_pid (inferior_ptid));
 
   fork_save_infrun_state (oldfp, 1);
-  inferior_ptid = newfp->ptid;
   fork_load_infrun_state (newfp);
-  registers_changed ();
-  reinit_frame_cache ();
-  stop_pc = read_pc ();
-  select_frame (get_current_frame ());
 
   printf_filtered (_("Switching to %s\n"), 
 		   target_pid_to_str (inferior_ptid));
Index: src/gdb/Makefile.in
===================================================================
--- src.orig/gdb/Makefile.in	2006-02-27 10:59:48.000000000 -0500
+++ src/gdb/Makefile.in	2006-02-27 11:12:35.000000000 -0500
@@ -726,6 +726,7 @@ kod_h = kod.h
 language_h = language.h
 libunwind_frame_h = libunwind-frame.h $(libunwind_h)
 linespec_h = linespec.h
+linux_fork_h = linux-fork.h
 linux_nat_h = linux-nat.h $(target_h)
 m2_lang_h = m2-lang.h
 m32r_tdep_h = m32r-tdep.h
@@ -2186,12 +2187,13 @@ linespec.o: linespec.c $(defs_h) $(symta
 	$(symfile_h) $(objfiles_h) $(source_h) $(demangle_h) $(value_h) \
 	$(completer_h) $(cp_abi_h) $(parser_defs_h) $(block_h) \
 	$(objc_lang_h) $(linespec_h) $(exceptions_h)
-linux-fork.o: linux-fork.c linux-fork.h $(defs_h) $(inferior_h) \
-	$(regcache_h) $(gdbcmd_h) $(infcall_h)
+linux-fork.o: linux-fork.c $(defs_h) $(inferior_h) $(regcache_h) $(gdbcmd_h) \
+	$(infcall_h) $(gdb_assert_h) $(gdb_string_h) $(linux_fork_h)
 linux-nat.o: linux-nat.c $(defs_h) $(inferior_h) $(target_h) $(gdb_string_h) \
 	$(gdb_wait_h) $(gdb_assert_h) $(linux_nat_h) $(gdbthread_h) \
 	$(gdbcmd_h) $(regcache_h) $(inf_ptrace.h) $(auxv.h) $(elf_bfd_h) \
-	$(gregset_h) $(gdbcore_h) $(gdbthread_h) $(gdb_stat_h) linux-fork.h
+	$(gregset_h) $(gdbcore_h) $(gdbthread_h) $(gdb_stat_h) \
+	$(linux_fork_h)
 linux-thread-db.o: linux-thread-db.c $(defs_h) $(gdb_assert_h) \
 	$(gdb_proc_service_h) $(gdb_thread_db_h) $(bfd_h) $(exceptions_h) \
 	$(gdbthread_h) $(inferior_h) $(symfile_h) $(objfiles_h) $(target_h) \


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