GDBserver: Don't assume a current process in D;PID implementation (PR gdb/23377)

This fixes a gdb.base/multi-forks.exp regression with GDBserver.

Git commit f2ffa92bbce9 ("gdb: Eliminate the 'stop_pc' global") caused
the regression by exposing a latent bug in gdbserver.

The bug is that GDBserver's implementation of the D;PID packet
incorrectly assumes that the selected thread points to the process
being detached.  This happens via the any_persistent_commands call,
which calls current_process:

  (gdb) bt
  #0  0x000000000040a57e in internal_error(char const*, int, char const*, ...)
  (file=0x4a53c0 "src/gdb/gdbserver/inferiors.c", line=212, fmt=0x4a539e "%s:
  Assertion `%s' failed.") at src/gdb/gdbserver/../common/errors.c:54
  #1  0x0000000000420acf in current_process() () at
  src/gdb/gdbserver/inferiors.c:212
  #2  0x00000000004226a0 in any_persistent_commands() () at
  gdb/gdbserver/mem-break.c:308
  #3  0x000000000042cb43 in handle_detach(char*) (own_buf=0x6f0280 "D;62ea") at
  src/gdb/gdbserver/server.c:1210
  #4  0x0000000000433af3 in process_serial_event() () at
  src/gdb/gdbserver/server.c:4055
  #5  0x0000000000434878 in handle_serial_event(int, void*) (err=0,
  client_data=0x0)

The "eliminate stop_pc" commit exposes the problem because before that
commit, GDB's switch_to_thread always read the newly-selected thread's
PC, and that would end up forcing GDBserver's selected thread to
change accordingly as side effect.  After that commit, GDB no longer
reads the thread's PC, and GDBserver does not switch the thread.

Fix this by removing the assumption from GDBserver.

gdb/gdbserver/ChangeLog:
2018-07-11  Pedro Alves  <palves@redhat.com>

	PR gdb/23377
	* mem-break.c (any_persistent_commands): Add process_info
	parameter and use it instead of relying on the current process.
	Change return type to bool.
	* mem-break.h (any_persistent_commands): Add process_info
	parameter and change return type to bool.
	* server.c (handle_detach): Remove require_running_or_return call.
	Look up the process_info for the process we're about to detach.
	If not found, return back error to GDB.  Adjust
	any_persistent_commands call to pass down a process pointer.

diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog
index 7c482b0ddfc2d468000a44c321c4923445c70568..f29ecea162179b12018872e285453cb1b8941732 100644 (file)
--- a/gdb/gdbserver/ChangeLog
+++ b/gdb/gdbserver/ChangeLog
@@ -1,3 +1,16 @@
+2018-07-11  Pedro Alves  <palves@redhat.com>
+
+       PR gdb/23377
+       * mem-break.c (any_persistent_commands): Add process_info
+       parameter and use it instead of relying on the current process.
+       Change return type to bool.
+       * mem-break.h (any_persistent_commands): Add process_info
+       parameter and change return type to bool.
+       * server.c (handle_detach): Remove require_running_or_return call.
+       Look up the process_info for the process we're about to detach.
+       If not found, return back error to GDB.  Adjust
+       any_persistent_commands call to pass down a process pointer.
+
 2018-07-11  Pedro Alves  <palves@redhat.com>
 
        * i387-fp.c (i387_cache_to_fsave, cache_to_fxsave)

diff --git a/gdb/gdbserver/mem-break.c b/gdb/gdbserver/mem-break.c
index 447afc7c10cd66026d465409f7273b9c8e8415b2..60f64bd3cbc16246181ff6199be6886b8704409a 100644 (file)
--- a/gdb/gdbserver/mem-break.c
+++ b/gdb/gdbserver/mem-break.c
@@ -302,10 +302,9 @@ is_gdb_breakpoint (enum bkpt_type type)
          || type == gdb_breakpoint_Z4);
 }
 
-int
-any_persistent_commands (void)
+bool
+any_persistent_commands (process_info *proc)
 {
-  struct process_info *proc = current_process ();
   struct breakpoint *bp;
   struct point_command_list *cl;
 
@@ -317,11 +316,11 @@ any_persistent_commands (void)
 
          for (cl = gdb_bp->command_list; cl != NULL; cl = cl->next)
            if (cl->persistence)
-             return 1;
+             return true;
        }
     }
 
-  return 0;
+  return false;
 }
 
 /* Find low-level breakpoint of type TYPE at address ADDR that is not

diff --git a/gdb/gdbserver/mem-break.h b/gdb/gdbserver/mem-break.h
index 019a87da09cba5ef1cfe62fd83cae1dd14308f81..7430c99883fe3bc1e745c0d87fce53d958a71b89 100644 (file)
--- a/gdb/gdbserver/mem-break.h
+++ b/gdb/gdbserver/mem-break.h
@@ -125,7 +125,8 @@ int add_breakpoint_condition (struct gdb_breakpoint *bp,
 int add_breakpoint_commands (struct gdb_breakpoint *bp, const char **commands,
                             int persist);
 
-int any_persistent_commands (void);
+/* Return true if PROC has any persistent command.  */
+bool any_persistent_commands (process_info *proc);
 
 /* Evaluation condition (if any) at breakpoint BP.  Return 1 if
    true and 0 otherwise.  */

diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index e5d226c1a46a9c7254964b05a5cc7b30be02b10b..bf6302ba2d18f94e3276fd2539eeed2bc0154729 100644 (file)
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -1195,34 +1195,37 @@ static void
 handle_detach (char *own_buf)
 {
   client_state &cs = get_client_state ();
-  require_running_or_return (own_buf);
 
-  int pid;
+  process_info *process;
 
   if (cs.multi_process)
     {
       /* skip 'D;' */
-      pid = strtol (&own_buf[2], NULL, 16);
+      int pid = strtol (&own_buf[2], NULL, 16);
+
+      process = find_process_pid (pid);
     }
   else
-    pid = current_ptid.pid ();
-
-  if ((tracing && disconnected_tracing) || any_persistent_commands ())
     {
-      struct process_info *process = find_process_pid (pid);
+      process = (current_thread != nullptr
+                ? get_thread_process (current_thread)
+                : nullptr);
+    }
 
-      if (process == NULL)
-       {
-         write_enn (own_buf);
-         return;
-       }
+  if (process == NULL)
+    {
+      write_enn (own_buf);
+      return;
+    }
 
+  if ((tracing && disconnected_tracing) || any_persistent_commands (process))
+    {
       if (tracing && disconnected_tracing)
        fprintf (stderr,
                 "Disconnected tracing in effect, "
                 "leaving gdbserver attached to the process\n");
 
-      if (any_persistent_commands ())
+      if (any_persistent_commands (process))
        fprintf (stderr,
                 "Persistent commands are present, "
                 "leaving gdbserver attached to the process\n");
@@ -1250,13 +1253,13 @@ handle_detach (char *own_buf)
       return;
     }
 
-  fprintf (stderr, "Detaching from process %d\n", pid);
+  fprintf (stderr, "Detaching from process %d\n", process->pid);
   stop_tracing ();
-  if (detach_inferior (pid) != 0)
+  if (detach_inferior (process->pid) != 0)
     write_enn (own_buf);
   else
     {
-      discard_queued_stop_replies (ptid_t (pid));
+      discard_queued_stop_replies (ptid_t (process->pid));
       write_ok (own_buf);
 
       if (extended_protocol || target_running ())
@@ -1266,7 +1269,7 @@ handle_detach (char *own_buf)
             and instead treat this like a normal program exit.  */
          cs.last_status.kind = TARGET_WAITKIND_EXITED;
          cs.last_status.value.integer = 0;
-         cs.last_ptid = ptid_t (pid);
+         cs.last_ptid = ptid_t (process->pid);
 
          current_thread = NULL;
        }
@@ -1278,7 +1281,7 @@ handle_detach (char *own_buf)
          /* If we are attached, then we can exit.  Otherwise, we
             need to hang around doing nothing, until the child is
             gone.  */
-         join_inferior (pid);
+         join_inferior (process->pid);
          exit (0);
        }
     }