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Re: [PATCH, ppc] Fix hw *points for embedded ppc in a threaded environment


One idea for less intrusive debugging would be to make it so
the kernel doesn't notified of new threads/clones at all, IOW, not
force parent/child clones to stop to report the child's existence to
a ptracer (unless it wants to).  Having the kernel auto-copy debug
resources in the new child is a requirement for that, and given
ptrace options and other things are copied as well, I can't
really call it broken outright.

I'd suggest just mixing something like

  Older kernels did not make new threads inherit their parent thread's
  debug state, so we always clear the slot and replicate the debug state
  ourselves, ensuring compatibility with all kernels.

into the existing comment.


The comment looked thorough enough that i went with it.

It does not:

+# Run to `main' where we begin our tests.
+if ![runto_main] then {
+    fail "Failed to run to main"
+}
+

Really done now.
Let's call "unsupported" or even FAIL then, so it can draw attention.
We could also end up in that situation due to a bug somewhere in the
test or gdb.  Something like 'fail "no hardware watchpoints"'.

Done.

+void empty_cycle (void)

'\n' after first void.

Done.


+for { set i 1 } { $i <= $TRIGGERS} { incr i} {
                             -------^    -----^
Missing spaces.


Done.

+# Move the threads and hit the watchpoints
+# TRIGGERS times.

Nit, that fits in a single line.

Done.


Otherwise OK.

Thanks! I'll check it in later today.

Luis

gdb/
2013-04-25  Luis Machado  <lgustavo@codesourcery.com>

	* ppc-linux-nat.c (ppc_linux_new_thread): Clear the new thread's
	debug state prior to replicating existing hardware watchpoints or
	breakpoints.

gdb/testsuite/
2013-04-25  Luis Machado  <lgustavo@codesourcery.com>

	gdb/testsuite
	* gdb.threads/wp-replication.c: New file.
	* gdb.threads/wp-replication.exp: New file.

Index: gdb-head/gdb/ppc-linux-nat.c
===================================================================
--- gdb-head.orig/gdb/ppc-linux-nat.c	2013-04-23 16:34:19.726438757 +0200
+++ gdb-head/gdb/ppc-linux-nat.c	2013-04-25 07:42:30.325296537 +0200
@@ -2178,7 +2178,18 @@ ppc_linux_new_thread (struct lwp_info *l
       /* Copy that thread's breakpoints and watchpoints to the new thread.  */
       for (i = 0; i < max_slots_number; i++)
 	if (hw_breaks[i].hw_break)
-	  booke_insert_point (hw_breaks[i].hw_break, tid);
+	  {
+	    /* Older kernels did not make new threads inherit their parent
+	       thread's debug state, so we always clear the slot and replicate
+	       the debug state ourselves, ensuring compatibility with all
+	       kernels.  */
+
+	    /* The ppc debug resource accounting is done through "slots".
+	       Ask the kernel the deallocate this specific *point's slot.  */
+	    ptrace (PPC_PTRACE_DELHWDEBUG, tid, 0, hw_breaks[i].slot);
+
+	    booke_insert_point (hw_breaks[i].hw_break, tid);
+	  }
     }
   else
     ptrace (PTRACE_SET_DEBUGREG, tid, 0, saved_dabr_value);
Index: gdb-head/gdb/testsuite/gdb.threads/wp-replication.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gdb-head/gdb/testsuite/gdb.threads/wp-replication.c	2013-04-25 07:23:24.281316900 +0200
@@ -0,0 +1,163 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2009-2013 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/>.
+
+   Check that hardware watchpoints get correctly replicated to all
+   existing threads when hardware watchpoints are created.  This test
+   creates one hardware watchpoint per thread until a maximum is
+   reached.  It originally addresses a deficiency seen on embedded
+   powerpc targets with slotted hardware *point designs.
+*/
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <pthread.h>
+
+#ifndef NR_THREADS
+#define NR_THREADS 4 /* Set by the testcase.  */
+#endif
+
+#ifndef X_INCR_COUNT
+#define X_INCR_COUNT 10 /* Set by the testcase.  */
+#endif
+
+void *thread_function (void *arg); /* Function executed by each thread.  */
+
+/* Used to hold threads back until wp-replication.exp is ready.  */
+int test_ready = 0;
+
+/* Used to hold threads back until every thread has had a chance of causing
+   a watchpoint trigger.  This prevents a situation in GDB where it may miss
+   watchpoint triggers when threads exit while other threads are causing
+   watchpoint triggers.  */
+int can_terminate = 0;
+
+/* Used to push the program out of the waiting loop after the
+   testcase is done counting the number of hardware watchpoints
+   available for our target.  */
+int watch_count_done = 0;
+
+/* Number of watchpoints GDB is capable of using (this is provided
+   by GDB during the test run).  */
+int hw_watch_count = 0;
+
+/* Array with elements we can create watchpoints for.  */
+static int watched_data[NR_THREADS];
+pthread_mutex_t data_mutex;
+
+/* Wait function to keep threads busy while the testcase does
+   what it needs to do.  */
+void
+empty_cycle (void)
+{
+  usleep (1);
+}
+
+int
+main ()
+{
+  int res;
+  pthread_t threads[NR_THREADS];
+  int i;
+
+  while (watch_count_done == 0)
+    {
+      /* GDB will modify the value of "i" at runtime and we will
+	 get past this point.  */
+      empty_cycle ();
+    }
+
+  pthread_mutex_init (&data_mutex, NULL);
+
+  for (i = 0; i < NR_THREADS; i++)
+    {
+      res = pthread_create (&threads[i],
+			    NULL, thread_function,
+			    (void *) (intptr_t) i);
+      if (res != 0)
+	{
+	  fprintf (stderr, "error in thread %d create\n", i);
+	  abort ();
+	}
+    }
+
+  for (i = 0; i < NR_THREADS; ++i)
+    {
+      res = pthread_join (threads[i], NULL);
+      if (res != 0)
+	{
+	  fprintf (stderr, "error in thread %d join\n", i);
+	  abort ();
+	}
+    }
+
+  exit (EXIT_SUCCESS);
+}
+
+/* Easy place for a breakpoint.
+   wp-replication.exp uses this to track when all threads are running
+   instead of, for example, the program keeping track
+   because we don't need the program to know when all threads are running,
+   instead we need gdb to know when all threads are running.
+   There is a delay between when a thread has started and when the thread
+   has been registered with gdb.  */
+
+void
+thread_started (void)
+{
+}
+
+void *
+thread_function (void *arg)
+{
+  int i, j;
+  long thread_number = (long) arg;
+
+  thread_started ();
+
+  /* Don't start incrementing X until wp-replication.exp is ready.  */
+  while (!test_ready)
+    usleep (1);
+
+  pthread_mutex_lock (&data_mutex);
+
+  for (i = 0; i < NR_TRIGGERS_PER_THREAD; i++)
+    {
+      for (j = 0; j < hw_watch_count; j++)
+	{
+	  /* For debugging.  */
+	  printf ("Thread %ld changing watch_thread[%d] data"
+	          " from %d -> %d\n", thread_number, j,
+	          watched_data[j], watched_data[j] + 1);
+	  /* Increment the watched data field.  */
+	  watched_data[j]++;
+	}
+    }
+
+  pthread_mutex_unlock (&data_mutex);
+
+  /* Hold the threads here to work around a problem GDB has evaluating
+     watchpoints right when a DSO event shows up (PR breakpoints/10116).
+     Sleep a little longer (than, say, 1, 5 or 10) to avoid consuming
+     lots of cycles while the other threads are trying to execute the
+     loop.  */
+  while (!can_terminate)
+    usleep (100);
+
+  pthread_exit (NULL);
+}
Index: gdb-head/gdb/testsuite/gdb.threads/wp-replication.exp
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ gdb-head/gdb/testsuite/gdb.threads/wp-replication.exp	2013-04-25 07:24:16.245315977 +0200
@@ -0,0 +1,151 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2009-2013 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/>.
+
+# Check that hardware watchpoints get correctly replicated to all
+# existing threads when hardware watchpoints are created.  This test
+# creates one hardware watchpoint per thread until a maximum is
+# reached.  It originally addresses a deficiency seen on embedded
+# powerpc targets with slotted hardware *point designs.
+
+set NR_THREADS 10
+set NR_TRIGGERS_PER_THREAD 2
+
+# This test verifies that a hardware watchpoint gets replicated to
+# every existing thread and is detected properly.  This test is
+# only meaningful on a target with hardware watchpoint support.
+if {[skip_hw_watchpoint_tests]} {
+    return 0
+}
+
+standard_testfile
+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable [list debug "additional_flags=-DNR_THREADS=$NR_THREADS -DNR_TRIGGERS_PER_THREAD=$NR_TRIGGERS_PER_THREAD"]] != "" } {
+    return -1
+}
+
+clean_restart ${binfile}
+
+# Force hardware watchpoints to be used.
+gdb_test_no_output "set can-use-hw-watchpoints 1" ""
+
+# Run to `main' where we begin our tests.
+if ![runto_main] then {
+    fail "Failed to run to main"
+    return 0
+}
+
+# First, break at empty_cycle.
+gdb_test "break empty_cycle" \
+  "Breakpoint 2 at .*: file .*${srcfile}, line .*" \
+  "Breakpoint on empty_cycle"
+
+# Set some default values.
+set hwatch_count 0
+set done 0
+
+# Count the number of hardware watchpoints available on
+# this target.
+while { $done == 0 } {
+
+  gdb_test "continue" \
+    ".*Breakpoint 2, empty_cycle \\(\\) at .*${srcfile}.*" \
+    "Continue to empty_cycle to insert watchpoint $hwatch_count"
+
+  # Some targets do resource counting as we insert watchpoints.
+  # Such targets won't cause a watchpoint insertion failure, but
+  # will switch to software watchpoints silently.  We check for
+  # both cases here.
+  gdb_test_multiple "watch watched_data\[$hwatch_count\]" \
+       "watch watched_data\[$hwatch_count\]" {
+    -re "Hardware watchpoint .*$gdb_prompt $" {
+    }
+    -re "Watchpoint .*$gdb_prompt $" {
+      set done 1
+      break
+    }
+  }
+
+  gdb_test_multiple "continue" "watchpoint created successfully" {
+    -re ".*Breakpoint 2, empty_cycle \\(\\).*$gdb_prompt $" {
+      incr hwatch_count
+    }
+    -re ".*Could not insert hardware watchpoint.*$gdb_prompt $" {
+      set done 1
+      break
+    }
+  }
+}
+
+# Target cannot insert hardware watchpoints.  It should have reported
+# (through board settings) that it did not support them in the first place.
+# Just exit.
+if { $hwatch_count == 0} {
+  fail "No hardware watchpoints available"
+  return 0
+}
+
+# Set the testcase's internal variable indicating the number of
+# hardware watchpoints the target supports.
+gdb_test_no_output "set var hw_watch_count=${hwatch_count}" \
+		   "set var hw_watch_count=${hwatch_count}"
+
+# At this point, we know how many hardware watchpoints
+# the target supports.  Use that to do further testing.
+delete_breakpoints
+
+# Break out of the empty_cycle loop by changing the
+# controlling variable.
+gdb_test_no_output "set var watch_count_done=1" \
+		   "set var watch_count_done=1"
+
+# Prepare to create all the threads.
+gdb_test "break thread_started" \
+	 "Breakpoint \[0-9\]+ at .*: file .*${srcfile}, line .*" \
+	 "Breakpoint on thread_started"
+
+# Move all threads to where they're supposed to be for testing.
+for { set i 0 } { $i < $NR_THREADS } { incr i } {
+
+    # We want to set the maximum number of hardware watchpoints
+    # and make sure the target can handle that without an error.
+    # That will show us the watchpoints got replicated to all the
+    # threads correctly, and that no new watchpoints got created
+    # in the background for a specific thread.
+    if {$i < $hwatch_count} {
+      gdb_test "watch watched_data\[$i\]" \
+	"Hardware watchpoint .*" \
+	"watch watched_data\[$i\]"
+    } else {
+      verbose -log "Not setting watchpoint for watched_data\[$i\]\n"
+    }
+
+    gdb_test continue "Continuing\\..*Breakpoint \[0-9\]+, thread_started \\(\\) at .*$srcfile.*" \
+    "Thread $i hit breakpoint at thread_started"
+}
+
+# Let the threads run and change the watched data, leading
+# to watchpoint triggers.
+gdb_test_no_output "set var test_ready=1" \
+      "set var test_ready=1"
+
+# Set the number of expected watchpoint triggers.
+set TRIGGERS [expr "$NR_THREADS * $hwatch_count * $NR_TRIGGERS_PER_THREAD"]
+
+# Move the threads and hit the watchpoints TRIGGERS times.
+for { set i 1 } { $i <= $TRIGGERS } { incr i } {
+    gdb_test continue "Continuing\\..*Hardware watchpoint \[0-9\]+: watched_data\[\[0-9\]+\].*Old value = \[0-9\]+.*New value = \[0-9\]+.*thread_function \\(arg=$hex\\) at .*$srcfile.*" \
+    "Continue to watchpoint trigger $i out of ${TRIGGERS} on watched_data"
+}

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