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Re: [patch] Fix linux-ia64 on SIGILL for deleted breakpoint


On Tue, 27 Jul 2010 13:43:16 +0200, Pedro Alves wrote:
> On Sunday 25 July 2010 19:52:17, Jan Kratochvil wrote:
> > On Sun, 25 Jul 2010 00:26:04 +0200, Pedro Alves wrote:

> If your check on s390 is good, than that might have broken (rare ...) corner
> cases on s390, like a SIGILL reported for an instruction set at the address
> consecutive to an inserted software breakpoint.

gdb/gdbserver/linux-low.c maybe_internal_trap may get set wrong on s390, OK.


> > Which arch uses gdbarch_decr_pc_after_break && generates a non-SIGTRAP signal
> > on a GDB-placed breakpoint?  It is probably none of the arches I target (i686,
> > x86_64, ppc{,64}, s390{,x}, ia64, possibly arm).
> 
> I don't have a list.  Some archs may generate that only on some
> situations (or used to and no longer do on more up to date versions).
                                                          kernel


> > > (Alternatively, recode to avoid the assumption)
> > 
> > Sorry I do not try to code anything without an iron to test it.
> 
> What I meant was to have your new code not depend on decr_pc_after
> break being 0, you don't need any other system to try that on.
> It meant, to not have any code path in the SIGILL
> case that calls gdbarch_decr_pc_after_break at all. Conceptually,
> something like:
> 
> if (sig == SIGTRAP && software_breakpoint_inserted_at (PC - decr_pc_after_breakpoint))
>  {
>     rewind pc, discard signal
>     return 1
>  }
> else if (sig == SIGILL && software_breakpoint_inserted_at (PC))
>  {
>     discard signal
>     return 1
>  }
> return 0

I believe we could need some ` - decr_pc_after_sigill' in the second
conditional as shown on the s390 case.  But only if GDB would place any such
SIGILL instruction so this paragraph is just a hand waving.

Not implementing this alternative way, thanks for the analysis.


> Okay.  Please fix the spelling of "alternative".

I am sorry.  Checked-in.


Thanks,
Jan


http://sourceware.org/ml/gdb-cvs/2010-07/msg00170.html

--- src/gdb/ChangeLog	2010/07/27 20:44:30	1.12025
+++ src/gdb/ChangeLog	2010/07/27 20:51:37	1.12026
@@ -1,3 +1,14 @@
+2010-07-27  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* ia64-linux-nat.c (ia64_linux_status_is_event): New function.
+	(_initialize_ia64_linux_nat): Install it.
+	* linux-nat.c (sigtrap_is_event, linux_nat_status_is_event)
+	(linux_nat_set_status_is_event): New.
+	(stop_wait_callback, count_events_callback, select_event_lwp_callback)
+	cancel_breakpoints_callback, linux_nat_filter_event)
+	(linux_nat_wait_1): Use linux_nat_status_is_event.
+	* linux-nat.h (linux_nat_set_status_is_event): New prototype.
+
 2010-07-27  Tom Tromey  <tromey@redhat.com>
 
 	* NEWS: Mention labels, .gdb_index.
--- src/gdb/ia64-linux-nat.c	2010/07/07 16:15:16	1.49
+++ src/gdb/ia64-linux-nat.c	2010/07/27 20:51:37	1.50
@@ -809,6 +809,18 @@
 			     offset, len);
 }
 
+/* For break.b instruction ia64 CPU forgets the immediate value and generates
+   SIGILL with ILL_ILLOPC instead of more common SIGTRAP with TRAP_BRKPT.
+   ia64 does not use gdbarch_decr_pc_after_break so we do not have to make any
+   difference for the signals here.  */
+
+static int
+ia64_linux_status_is_event (int status)
+{
+  return WIFSTOPPED (status) && (WSTOPSIG (status) == SIGTRAP
+				 || WSTOPSIG (status) == SIGILL);
+}
+
 void _initialize_ia64_linux_nat (void);
 
 void
@@ -848,4 +860,5 @@
   /* Register the target.  */
   linux_nat_add_target (t);
   linux_nat_set_new_thread (t, ia64_linux_new_thread);
+  linux_nat_set_status_is_event (t, ia64_linux_status_is_event);
 }
--- src/gdb/linux-nat.c	2010/07/25 09:31:12	1.178
+++ src/gdb/linux-nat.c	2010/07/27 20:51:37	1.179
@@ -2605,6 +2605,29 @@
   return lp->stopped_data_address_p;
 }
 
+/* Commonly any breakpoint / watchpoint generate only SIGTRAP.  */
+
+static int
+sigtrap_is_event (int status)
+{
+  return WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP;
+}
+
+/* SIGTRAP-like events recognizer.  */
+
+static int (*linux_nat_status_is_event) (int status) = sigtrap_is_event;
+
+/* Set alternative SIGTRAP-like events recognizer.  If
+   breakpoint_inserted_here_p there then gdbarch_decr_pc_after_break will be
+   applied.  */
+
+void
+linux_nat_set_status_is_event (struct target_ops *t,
+			       int (*status_is_event) (int status))
+{
+  linux_nat_status_is_event = status_is_event;
+}
+
 /* Wait until LP is stopped.  */
 
 static int
@@ -2645,7 +2668,7 @@
 
       if (WSTOPSIG (status) != SIGSTOP)
 	{
-	  if (WSTOPSIG (status) == SIGTRAP)
+	  if (linux_nat_status_is_event (status))
 	    {
 	      /* If a LWP other than the LWP that we're reporting an
 	         event for has hit a GDB breakpoint (as opposed to
@@ -2801,7 +2824,7 @@
 
   /* Count only resumed LWPs that have a SIGTRAP event pending.  */
   if (lp->status != 0 && lp->resumed
-      && WIFSTOPPED (lp->status) && WSTOPSIG (lp->status) == SIGTRAP)
+      && linux_nat_status_is_event (lp->status))
     (*count)++;
 
   return 0;
@@ -2829,7 +2852,7 @@
 
   /* Select only resumed LWPs that have a SIGTRAP event pending. */
   if (lp->status != 0 && lp->resumed
-      && WIFSTOPPED (lp->status) && WSTOPSIG (lp->status) == SIGTRAP)
+      && linux_nat_status_is_event (lp->status))
     if ((*selector)-- == 0)
       return 1;
 
@@ -2891,7 +2914,7 @@
 
   if (lp->waitstatus.kind == TARGET_WAITKIND_IGNORE
       && lp->status != 0
-      && WIFSTOPPED (lp->status) && WSTOPSIG (lp->status) == SIGTRAP
+      && linux_nat_status_is_event (lp->status)
       && cancel_breakpoint (lp))
     /* Throw away the SIGTRAP.  */
     lp->status = 0;
@@ -3064,7 +3087,7 @@
 	return NULL;
     }
 
-  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP)
+  if (linux_nat_status_is_event (status))
     {
       /* Save the trap's siginfo in case we need it later.  */
       save_siginfo (lp);
@@ -3411,7 +3434,7 @@
 			 threads.  */
 		      if (non_stop
 			  && lp->waitstatus.kind == TARGET_WAITKIND_IGNORE
-			  && WSTOPSIG (lp->status) == SIGTRAP
+			  && linux_nat_status_is_event (lp->status)
 			  && cancel_breakpoint (lp))
 			{
 			  /* Throw away the SIGTRAP.  */
@@ -3627,7 +3650,7 @@
   else
     lp->resumed = 0;
 
-  if (WIFSTOPPED (status) && WSTOPSIG (status) == SIGTRAP)
+  if (linux_nat_status_is_event (status))
     {
       if (debug_linux_nat)
 	fprintf_unfiltered (gdb_stdlog,
--- src/gdb/linux-nat.h	2010/06/11 12:10:12	1.35
+++ src/gdb/linux-nat.h	2010/07/27 20:51:37	1.36
@@ -172,3 +172,7 @@
 
 /* Compute and return the processor core of a given thread.  */
 int linux_nat_core_of_thread_1 (ptid_t ptid);
+
+/* Set alternative SIGTRAP-like events recognizer.  */
+void linux_nat_set_status_is_event (struct target_ops *t,
+				    int (*status_is_event) (int status));
--- src/gdb/testsuite/ChangeLog	2010/07/27 18:08:47	1.2391
+++ src/gdb/testsuite/ChangeLog	2010/07/27 20:51:37	1.2392
@@ -1,3 +1,8 @@
+2010-07-27  Jan Kratochvil  <jan.kratochvil@redhat.com>
+
+	* gdb.threads/ia64-sigill.exp: New file.
+	* gdb.threads/ia64-sigill.c: New file.
+
 2010-07-27  Tom Tromey  <tromey@redhat.com>
 
 	* gdb.opt/inline-cmds.c (ATTR): New define.
--- src/gdb/testsuite/gdb.threads/ia64-sigill.c
+++ src/gdb/testsuite/gdb.threads/ia64-sigill.c	2010-07-27 20:51:55.245809000 +0000
@@ -0,0 +1,360 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2010 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/>.  */
+
+#define _GNU_SOURCE
+#include <pthread.h>
+#include <stdio.h>
+#include <limits.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <sys/types.h>
+#include <signal.h>
+#include <unistd.h>
+#include <asm/unistd.h>
+
+#define gettid() syscall (__NR_gettid)
+
+/* Terminate always in the main task, it can lock up with SIGSTOPped GDB
+   otherwise.  */
+#define TIMEOUT (gettid () == getpid() ? 10 : 15)
+
+static pid_t thread1_tid;
+static pthread_cond_t thread1_tid_cond = PTHREAD_COND_INITIALIZER;
+static pthread_mutex_t thread1_tid_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
+
+static pid_t thread2_tid;
+static pthread_cond_t thread2_tid_cond = PTHREAD_COND_INITIALIZER;
+static pthread_mutex_t thread2_tid_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
+
+static pthread_mutex_t terminate_mutex = PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP;
+
+/* Do not use alarm as it would create a ptrace event which would hang up us if
+   we are being traced by GDB which we stopped ourselves.  */
+
+static void timed_mutex_lock (pthread_mutex_t *mutex)
+{
+  int i;
+  struct timespec start, now;
+
+  i = clock_gettime (CLOCK_MONOTONIC, &start);
+  assert (i == 0);
+
+  do
+    {
+      i = pthread_mutex_trylock (mutex);
+      if (i == 0)
+	return;
+      assert (i == EBUSY);
+
+      i = clock_gettime (CLOCK_MONOTONIC, &now);
+      assert (i == 0);
+      assert (now.tv_sec >= start.tv_sec);
+    }
+  while (now.tv_sec - start.tv_sec < TIMEOUT);
+
+  fprintf (stderr, "Timed out waiting for internal lock!\n");
+  exit (EXIT_FAILURE);
+}
+
+static void *
+thread_func (void *threadno_voidp)
+{
+  int threadno = (intptr_t) threadno_voidp;
+  int i;
+
+  switch (threadno)
+  {
+    case 1:
+      timed_mutex_lock (&thread1_tid_mutex);
+
+      /* THREAD1_TID_MUTEX must be already locked to avoid race.  */
+      thread1_tid = gettid ();
+
+      i = pthread_cond_signal (&thread1_tid_cond);
+      assert (i == 0);
+      i = pthread_mutex_unlock (&thread1_tid_mutex);
+      assert (i == 0);
+
+      break;
+
+    case 2:
+      timed_mutex_lock (&thread2_tid_mutex);
+
+      /* THREAD2_TID_MUTEX must be already locked to avoid race.  */
+      thread2_tid = gettid ();
+
+      i = pthread_cond_signal (&thread2_tid_cond);
+      assert (i == 0);
+      i = pthread_mutex_unlock (&thread2_tid_mutex);
+      assert (i == 0);
+
+      break;
+
+    default:
+      assert (0);
+  }
+
+#ifdef __ia64__
+  asm volatile ("label:\n"
+		"nop.m 0\n"
+		"nop.i 0\n"
+		"nop.b 0\n");
+#endif
+  /* break-here */
+
+  /* Be sure the "t (tracing stop)" test can proceed for both threads.  */
+  timed_mutex_lock (&terminate_mutex);
+  i = pthread_mutex_unlock (&terminate_mutex);
+  assert (i == 0);
+
+  return NULL;
+}
+
+static const char *
+proc_string (const char *filename, const char *line)
+{
+  FILE *f;
+  static char buf[LINE_MAX];
+  size_t line_len = strlen (line);
+
+  f = fopen (filename, "r");
+  if (f == NULL)
+    {
+      fprintf (stderr, "fopen (\"%s\") for \"%s\": %s\n", filename, line,
+	       strerror (errno));
+      exit (EXIT_FAILURE);
+    }
+  while (errno = 0, fgets (buf, sizeof (buf), f))
+    {
+      char *s;
+
+      s = strchr (buf, '\n');
+      assert (s != NULL);
+      *s = 0;
+
+      if (strncmp (buf, line, line_len) != 0)
+	continue;
+
+      if (fclose (f))
+	{
+	  fprintf (stderr, "fclose (\"%s\") for \"%s\": %s\n", filename, line,
+		   strerror (errno));
+	  exit (EXIT_FAILURE);
+	}
+
+      return &buf[line_len];
+    }
+  if (errno != 0)
+    {
+      fprintf (stderr, "fgets (\"%s\": %s\n", filename, strerror (errno));
+      exit (EXIT_FAILURE);
+    }
+  fprintf (stderr, "\"%s\": No line \"%s\" found.\n", filename, line);
+  exit (EXIT_FAILURE);
+}
+
+static unsigned long
+proc_ulong (const char *filename, const char *line)
+{
+  const char *s = proc_string (filename, line);
+  long retval;
+  char *end;
+
+  errno = 0;
+  retval = strtol (s, &end, 10);
+  if (retval < 0 || retval >= LONG_MAX || (end && *end))
+    {
+      fprintf (stderr, "\"%s\":\"%s\": %ld, %s\n", filename, line, retval,
+	       strerror (errno));
+      exit (EXIT_FAILURE);
+    }
+  return retval;
+}
+
+static void
+state_wait (pid_t process, const char *wanted)
+{
+  char *filename;
+  int i;
+  struct timespec start, now;
+  const char *state;
+
+  i = asprintf (&filename, "/proc/%lu/status", (unsigned long) process);
+  assert (i > 0);
+
+  i = clock_gettime (CLOCK_MONOTONIC, &start);
+  assert (i == 0);
+
+  do
+    {
+      state = proc_string (filename, "State:\t");
+
+      /* torvalds/linux-2.6.git 464763cf1c6df632dccc8f2f4c7e50163154a2c0
+	 has changed "T (tracing stop)" to "t (tracing stop)".  Make the GDB
+	 testcase backward compatible with older Linux kernels.  */
+      if (strcmp (state, "T (tracing stop)") == 0)
+	state = "t (tracing stop)";
+
+      if (strcmp (state, wanted) == 0)
+	{
+	  free (filename);
+	  return;
+	}
+
+      if (sched_yield ())
+	{
+	  perror ("sched_yield()");
+	  exit (EXIT_FAILURE);
+	}
+
+      i = clock_gettime (CLOCK_MONOTONIC, &now);
+      assert (i == 0);
+      assert (now.tv_sec >= start.tv_sec);
+    }
+  while (now.tv_sec - start.tv_sec < TIMEOUT);
+
+  fprintf (stderr, "Timed out waiting for PID %lu \"%s\" (now it is \"%s\")!\n",
+	   (unsigned long) process, wanted, state);
+  exit (EXIT_FAILURE);
+}
+
+static volatile pid_t tracer = 0;
+static pthread_t thread1, thread2;
+
+static void
+cleanup (void)
+{
+  printf ("Resuming GDB PID %lu.\n", (unsigned long) tracer);
+
+  if (tracer)
+    {
+      int i;
+      int tracer_save = tracer;
+
+      tracer = 0;
+
+      i = kill (tracer_save, SIGCONT);
+      assert (i == 0);
+    }
+}
+
+int
+main (int argc, char **argv)
+{
+  int i;
+  int standalone = 0;
+
+  if (argc == 2 && strcmp (argv[1], "-s") == 0)
+    standalone = 1;
+  else
+    assert (argc == 1);
+
+  setbuf (stdout, NULL);
+
+  timed_mutex_lock (&thread1_tid_mutex);
+  timed_mutex_lock (&thread2_tid_mutex);
+
+  timed_mutex_lock (&terminate_mutex);
+
+  i = pthread_create (&thread1, NULL, thread_func, (void *) (intptr_t) 1);
+  assert (i == 0);
+
+  i = pthread_create (&thread2, NULL, thread_func, (void *) (intptr_t) 2);
+  assert (i == 0);
+
+  if (!standalone)
+    {
+      tracer = proc_ulong ("/proc/self/status", "TracerPid:\t");
+      if (tracer == 0)
+	{
+	  fprintf (stderr, "The testcase must be run by GDB!\n");
+	  exit (EXIT_FAILURE);
+	}
+      if (tracer != getppid ())
+	{
+	  fprintf (stderr, "The testcase parent must be our GDB tracer!\n");
+	  exit (EXIT_FAILURE);
+	}
+    }
+
+  /* SIGCONT our debugger in the case of our crash as we would deadlock
+     otherwise.  */
+
+  atexit (cleanup);
+
+  printf ("Stopping GDB PID %lu.\n", (unsigned long) tracer);
+
+  if (tracer)
+    {
+      i = kill (tracer, SIGSTOP);
+      assert (i == 0);
+      state_wait (tracer, "T (stopped)");
+    }
+
+  /* Threads are now waiting at timed_mutex_lock (thread1_tid_mutex) and so
+     they could not trigger the breakpoint before GDB gets unstopped later.
+     Threads get resumed at pthread_cond_wait below.  Use `while' loops for
+     protection against spurious pthread_cond_wait wakeups.  */
+
+  printf ("Waiting till the threads initialize their TIDs.\n");
+
+  while (thread1_tid == 0)
+    {
+      i = pthread_cond_wait (&thread1_tid_cond, &thread1_tid_mutex);
+      assert (i == 0);
+    }
+
+  while (thread2_tid == 0)
+    {
+      i = pthread_cond_wait (&thread2_tid_cond, &thread2_tid_mutex);
+      assert (i == 0);
+    }
+
+  printf ("Thread 1 TID = %lu, thread 2 TID = %lu, PID = %lu.\n",
+	  (unsigned long) thread1_tid, (unsigned long) thread2_tid,
+	  (unsigned long) getpid ());
+
+  printf ("Waiting till the threads get trapped by the breakpoint.\n");
+
+  if (tracer)
+    {
+      /* s390x-unknown-linux-gnu will fail with "R (running)".  */
+
+      state_wait (thread1_tid, "t (tracing stop)");
+
+      state_wait (thread2_tid, "t (tracing stop)");
+    }
+
+  cleanup ();
+
+  printf ("Joining the threads.\n");
+
+  i = pthread_mutex_unlock (&terminate_mutex);
+  assert (i == 0);
+
+  i = pthread_join (thread1, NULL);
+  assert (i == 0);
+
+  i = pthread_join (thread2, NULL);
+  assert (i == 0);
+
+  printf ("Exiting.\n");	/* break-at-exit */
+
+  return EXIT_SUCCESS;
+}
--- src/gdb/testsuite/gdb.threads/ia64-sigill.exp
+++ src/gdb/testsuite/gdb.threads/ia64-sigill.exp	2010-07-27 20:51:55.778901000 +0000
@@ -0,0 +1,76 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2010 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 SIGILL generated by some special cases of breakpoints on ia64.  Problem
+# was SIGILL being stored in non-current thread for later retrieval when its
+# breakpoint has been already deleted.  moribund locations are not active in
+# the default all-stop mode.
+
+set testfile "ia64-sigill"
+set srcfile ${testfile}.c
+set binfile ${objdir}/${subdir}/${testfile}
+if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" ${binfile} executable [list debug additional_flags=-lrt]] != "" } {
+    return -1
+}
+
+clean_restart $testfile
+
+if ![runto_main] {
+    return -1
+}
+
+set test "info addr label"
+gdb_test_multiple $test $test {
+    -re "Symbol \"label\" is at 0x\[0-9a-f\]+0 in .*\r\n$gdb_prompt $" {
+	# Verify the label really starts at the start of ia64 bundle.
+	pass $test
+
+	# ia64 generates SIGILL for breakpoint at B slot of an MIB bundle.
+	gdb_test "break *label+2" {Breakpoint [0-9]+ at 0x[0-9a-f]+2:.*}
+    }
+    -re "No symbol \"label\" in current context\\.\r\n$gdb_prompt $" {
+	pass $test
+
+	# Either this target never generates non-SIGTRAP signals or they do
+	# not depend on the breakpoint address.  Try any address.
+	gdb_breakpoint [gdb_get_line_number "break-here"]
+    }
+}
+
+gdb_test_no_output {set $sigill_bpnum=$bpnum}
+
+gdb_breakpoint [gdb_get_line_number "break-at-exit"]
+
+gdb_test_no_output "set debug infrun 1"
+
+# The ia64 SIGILL signal is visible only in the lin-lwp debug.
+gdb_test_no_output "set debug lin-lwp 1"
+
+gdb_test "continue" "Breakpoint \[0-9\]+,( .* in)? thread_func .*"
+
+gdb_test_no_output {delete $sigill_bpnum}
+
+set test "continue for the pending signal"
+gdb_test_multiple "continue" $test {
+    -re "Breakpoint \[0-9\]+, .*break-at-exit.*\r\n$gdb_prompt $" {
+	# Breakpoint has been skipped in the other thread.
+	pass $test
+    }
+    -re "Program received signal .*\r\n$gdb_prompt $" {
+	fail $test
+    }
+}


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