gdb/gdbserver/

* linux-low.c (linux_wait_for_event): Don't clear the `stepping'
	flag.
	(wait_for_sigstop): Don't leave a finished single-step SIGTRAP
	pending.
	(linux_continue_one_thread): Only preserve the stepping flag if
	there's a pending breakpoint.

gdb/testsuite/

	* gdb.threads/pending-step.c, gdb.threads/pending-step.exp: New.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,12 @@
+2009-04-01  Pedro Alves  <pedro@codesourcery.com>
+
+	* linux-low.c (linux_wait_for_event): Don't clear the `stepping'
+	flag.
+	(wait_for_sigstop): Don't leave a finished single-step SIGTRAP
+	pending.
+	(linux_continue_one_thread): Only preserve the stepping flag if
+	there's a pending breakpoint.
+
 2009-03-31  Pedro Alves  <pedro@codesourcery.com>
 
 	* server.c (main): After the inferior having exited, call

gdb/gdbserver/linux-low.c

@@ -122,6 +122,7 @@ static int linux_wait_for_event (struct thread_info *child);
 static int check_removed_breakpoint (struct lwp_info *event_child);
 static void *add_lwp (unsigned long pid);
 static int my_waitpid (int pid, int *status, int flags);
+static int linux_stopped_by_watchpoint (void);
 
 struct pending_signals
 {
@@ -899,19 +900,11 @@ linux_wait_for_event (struct thread_info *child)
 	fprintf (stderr, "Hit a non-gdbserver breakpoint.\n");
 
       /* If we were single-stepping, we definitely want to report the
-	 SIGTRAP.  The single-step operation has completed, so also
+	 SIGTRAP.  Although the single-step operation has completed,
-	 clear the stepping flag; in general this does not matter,
+	 do not clear clear the stepping flag yet; we need to check it
-	 because the SIGTRAP will be reported to the client, which
+	 in wait_for_sigstop.  */
-	 will give us a new action for this thread, but clear it for
-	 consistency anyway.  It's safe to clear the stepping flag
-	 because the only consumer of get_stop_pc () after this point
-	 is check_removed_breakpoint, and pending_is_breakpoint is not
-	 set.  It might be wiser to use a step_completed flag instead.  */
       if (event_child->stepping)
-	{
+	return wstat;
-	  event_child->stepping = 0;
-	  return wstat;
-	}
 
       /* A SIGTRAP that we can't explain.  It may have been a breakpoint.
 	 Check if it is a breakpoint, and if so mark the process information
@@ -1097,8 +1090,24 @@ wait_for_sigstop (struct inferior_list_entry *entry)
       if (debug_threads)
 	fprintf (stderr, "LWP %ld stopped with non-sigstop status %06x\n",
 		 lwp->lwpid, wstat);
-      lwp->status_pending_p = 1;
+
-      lwp->status_pending = wstat;
+      /* Do not leave a pending single-step finish to be reported to
+	 the client.  The client will give us a new action for this
+	 thread, possibly a continue request --- otherwise, the client
+	 would consider this pending SIGTRAP reported later a spurious
+	 signal.  */
+      if (WSTOPSIG (wstat) == SIGTRAP
+	  && lwp->stepping
+	  && !linux_stopped_by_watchpoint ())
+	{
+	  if (debug_threads)
+	    fprintf (stderr, "  single-step SIGTRAP ignored\n");
+	}
+      else
+	{
+	  lwp->status_pending_p = 1;
+	  lwp->status_pending = wstat;
+	}
       lwp->stop_expected = 1;
     }
 
@@ -1283,8 +1292,10 @@ linux_continue_one_thread (struct inferior_list_entry *entry)
   if (lwp->resume->leave_stopped)
     return;
 
-  if (lwp->resume->thread == -1)
+  if (lwp->resume->thread == -1
-    step = lwp->stepping || lwp->resume->step;
+      && lwp->stepping
+      && lwp->pending_is_breakpoint)
+    step = 1;
   else
     step = lwp->resume->step;
 

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2009-04-01  Pedro Alves  <pedro@codesourcery.com>
+
+	* gdb.threads/pending-step.c, gdb.threads/pending-step.exp: New.
+
 2009-04-01  Tom Tromey  <tromey@redhat.com>
 
 	* gdb.base/funcargs.exp: Set print frame-arguments to "all".

gdb/testsuite/gdb.threads/pending-step.c

@@ -0,0 +1,61 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2002, 2003, 2004, 2007, 2008, 2009 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <unistd.h>
+#include <stdlib.h>
+#include <pthread.h>
+
+void *thread_function(void *arg); /* Pointer to function executed by each thread */
+
+#define NUM 1
+
+unsigned int args[NUM+1];
+
+int main() {
+    int res;
+    pthread_t threads[NUM];
+    void *thread_result;
+    long i;
+
+    for (i = 1; i <= NUM; i++)
+      {
+	args[i] = 1;
+	res = pthread_create(&threads[i],
+		             NULL,
+			     thread_function,
+			     (void *) i);
+      }
+
+    /* schedlock.exp: last thread start.  */
+    args[0] = 1;
+    thread_function ((void *) 0);
+
+    exit(EXIT_SUCCESS);
+}
+
+void *thread_function(void *arg) {
+    int my_number =  (long) arg;
+    int *myp = (int *) &args[my_number];
+
+    /* Don't run forever.  Run just short of it :)  */
+    while (*myp > 0)
+      {
+	(*myp) ++; /* insert breakpoint here */
+      }
+
+    pthread_exit(NULL);
+}

gdb/testsuite/gdb.threads/pending-step.exp

@@ -0,0 +1,95 @@
+# Copyright (C) 2009 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test that a resume cancels a previously unfinished or unreported
+# single-step correctly.
+#
+# The test consists of several threads all running the same loop.
+# There is a breakpoint set in the loop, hence all threads may hit it.
+# The test then issues several "next" commands in a loop.
+#
+# scheduler-locking must be set to the default of "off".
+#
+# Here's what would happen in gdbserver:
+#
+# 1) We issue a "continue", and wait until a thread hits the
+#    breakpoint.  Could be any thread, but assume thread 1 hits it.
+#
+# 2) We issue a "next" --- this single-steps thread 1, and resumes all
+#    other threads.
+#
+# 3) thread 2, due to scheduler-locking off, hits the breakpoint.
+#    gdbserver stops all other threads by sending them SIGSTOPs.
+#
+# 4) While being stopped in step 3, thread 1 reports a SIGTRAP, that
+#    corresponds to the finished single-step of step 2.  gdbserver
+#    leaves the SIGTRAP pending to report later.
+#
+# 5) We issue another "next" --- this requests thread 2 to
+#    single-step, and all other threads to continue, including thread
+#    1.  Before resuming any thread, gdbserver notices that it
+#    remembers from step 4 a pending SIGTRAP to report for thread 1,
+#    so reports it now.
+#
+# 6) From GDB's perpective, this SIGTRAP can't represent a finished
+#    single-step, since thread 1 was not single-stepping (it was
+#    continued in step 5).  Neither does this SIGTRAP correspond to a
+#    breakpoint hit.  GDB reports to the user a spurious SIGTRAP.
+
+set testfile "pending-step"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+
+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable [list debug "incdir=${objdir}"]] != "" } {
+    return -1
+}
+
+# Start with a fresh gdb.
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+if ![runto_main] then {
+    fail "Can't run to main"
+    return 0
+}
+
+gdb_breakpoint [gdb_get_line_number "insert breakpoint here"]
+gdb_continue_to_breakpoint "continue to first breakpoint hit"
+
+set test "next in multiple threads with breakpoints"
+set iterations 20
+set ok 0
+for {set i 0} {$i < $iterations} {incr i} {
+    set ok 0
+    gdb_test_multiple "next" "$test" {
+	-re "SIGTRAP.*$gdb_prompt $" {
+	    fail "$test (spurious SIGTRAP)"
+	}
+	-re "$gdb_prompt $" {
+	    set ok 1
+	}
+    }
+
+    if { $ok == 0 } {
+	break
+    }
+}
+
+if { $ok  } {
+    pass "$test"
+}