[binutils-gdb] Fix setting watchpoints when current thread is running

[binutils-gdb] Fix setting watchpoints when current thread is running

[Pedro Alves]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=c223d3738832011ced54e8415fa218934aebd0e4

commit c223d3738832011ced54e8415fa218934aebd0e4
Author: Pedro Alves <pedro@palves.net>
Date:   Tue May 2 15:04:28 2023 +0100

    Fix setting watchpoints when current thread is running
    
    Currently, when the current thread is running, you can print global
    variables.  However, if you try to set a watchpoint on the same
    globals, GDB errors out, complaining that the selected thread is
    running.  Like so:
    
     (gdb) c&
     Continuing.
     (gdb) p global
     $1 = 1098377287
     (gdb) watch global
     Selected thread is running.
    
    This patch makes setting the watchpoint work.  You'll now get:
    
     (gdb) c&
     Continuing.
     (gdb) [New Thread 0x7ffff7d6e640 (LWP 434993)]
     [New Thread 0x7ffff756d640 (LWP 434994)]
     p global
     $1 = 88168
     (gdb) watch global
     Hardware watchpoint 2: global
     (gdb) [Switching to Thread 0x7ffff7d6e640 (LWP 434993)]
    
     Thread 2 "function0" hit Hardware watchpoint 2: global
    
     Old value = 185420
     New value = 185423
     int_return () at threads.c:39
     39      }
    
    The problem is that update_watchpoint calls get_selected_frame
    unconditionally.  We can skip it if the watchpoint expression is only
    watching globals.
    
    This adds a testcase that exercises both all-stop and non-stop, and
    also software and hardware watchpoints.  It is kfailed for software
    watchpoints, as those require another fix not handled by this patch
    (the sw watchpoint doesn't fire because GDB doesn't force the
    running-free thread to switch to single-stepping).
    
    Change-Id: I68ca948541aea3edd4f70741f272f543187abe40

Diff:
---
 gdb/breakpoint.c                              |  11 +-
 gdb/testsuite/gdb.base/watchpoint-running.c   |  46 +++++++++
 gdb/testsuite/gdb.base/watchpoint-running.exp | 139 ++++++++++++++++++++++++++
 3 files changed, 192 insertions(+), 4 deletions(-)

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index ea89c40ce26..6d8adc62664 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -2153,7 +2153,7 @@ update_watchpoint (struct watchpoint *b, bool reparse)
     {
       std::vector<value_ref_ptr> val_chain;
       struct value *v, *result;
-      struct program_space *frame_pspace;
+      struct program_space *wp_pspace;
 
       fetch_subexp_value (b->exp.get (), b->exp->op.get (), &v, &result,
 			  &val_chain, false);
@@ -2172,7 +2172,10 @@ update_watchpoint (struct watchpoint *b, bool reparse)
 	  b->val_valid = true;
 	}
 
-      frame_pspace = get_frame_program_space (get_selected_frame (NULL));
+      if (b->exp_valid_block == nullptr)
+	wp_pspace = current_program_space;
+      else
+	wp_pspace = get_frame_program_space (get_selected_frame (NULL));
 
       /* Look at each value on the value chain.  */
       gdb_assert (!val_chain.empty ());
@@ -2232,7 +2235,7 @@ update_watchpoint (struct watchpoint *b, bool reparse)
 
 		  bp_location *loc = b->allocate_location ();
 		  loc->gdbarch = v->type ()->arch ();
-		  loc->pspace = frame_pspace;
+		  loc->pspace = wp_pspace;
 		  loc->address
 		    = gdbarch_remove_non_address_bits (loc->gdbarch, addr);
 		  b->add_location (*loc);
@@ -2357,7 +2360,7 @@ update_watchpoint (struct watchpoint *b, bool reparse)
 	 bpstat_stop_status requires a location to be able to report
 	 stops, so make sure there's at least a dummy one.  */
       if (b->type == bp_watchpoint && !b->has_locations ())
-	add_dummy_location (b, frame_pspace);
+	add_dummy_location (b, wp_pspace);
     }
   else if (!within_current_scope)
     {
diff --git a/gdb/testsuite/gdb.base/watchpoint-running.c b/gdb/testsuite/gdb.base/watchpoint-running.c
new file mode 100644
index 00000000000..3ba1cb21dfe
--- /dev/null
+++ b/gdb/testsuite/gdb.base/watchpoint-running.c
@@ -0,0 +1,46 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2023-2024 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 <stdint.h>
+
+uint64_t global_var;
+
+/* How long to usleep, in us.  The exp file assumes this is lower than
+   1s.  */
+#define MS_USLEEP 100000
+
+/* How many increments per second MS_USLEEP corresponds to.  */
+#define INCREMENTS_PER_SEC (1000000 / MS_USLEEP)
+
+int
+main ()
+{
+  while (1)
+    {
+      usleep (MS_USLEEP);
+      global_var++;
+
+      /* Time out after 30s.  */
+      if (global_var >= (30 * INCREMENTS_PER_SEC))
+	return 1;
+    }
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/watchpoint-running.exp b/gdb/testsuite/gdb.base/watchpoint-running.exp
new file mode 100644
index 00000000000..d0510f8555c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/watchpoint-running.exp
@@ -0,0 +1,139 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2023-2024 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/>.
+
+# This test verifies that you can set a watchpoint that watches global
+# memory, when the selected thread is running.
+
+#require allow_hw_watchpoint_multi_tests
+
+set allow_hw_watchpoint_tests_p [allow_hw_watchpoint_tests]
+
+standard_testfile
+
+if [build_executable "failed to prepare" $testfile $srcfile {debug}] {
+    return -1
+}
+
+# STOP_MODE is either "all-stop" or "non-stop".  HW is true if we are
+# testing hardware watchpoints, and false if we're testing software
+# watchpoints.
+
+proc test {stop_mode hw} {
+
+    save_vars { ::GDBFLAGS } {
+	if { $stop_mode == "non-stop" } {
+	    append ::GDBFLAGS " -ex \"set non-stop on\""
+	} elseif {[target_info gdb_protocol] == "remote"
+		  || [target_info gdb_protocol]== "extended-remote"} {
+	    # Communicating with the target while the inferior is
+	    # running depends on target running in non-stop mode.
+	    # Force it on for remote targets, until this is the
+	    # default.
+	    append ::GDBFLAGS " -ex \"maint set target-non-stop on\""
+	}
+	clean_restart $::binfile
+    }
+
+    gdb_test_no_output "set can-use-hw-watchpoints $hw"
+
+    if {![runto_main]} {
+	return
+    }
+
+    delete_breakpoints
+
+    # Continue the program in the background.
+    set test "continue&"
+    gdb_test_multiple "continue&" $test {
+	-re "Continuing\\.\r\n$::gdb_prompt " {
+	    pass $test
+	}
+    }
+
+    set val1 ""
+    gdb_test_multiple "print global_var" "global_var once" {
+	-re -wrap " = ($::decimal)" {
+	    set val1 $expect_out(1,string)
+	    pass "$gdb_test_name"
+	}
+    }
+
+    # Sleep for a bit, so the variable is sure to be incremented, if
+    # indeed we managed to get the target running.
+    sleep 1
+
+    set val2 ""
+    gdb_test_multiple "print global_var" "global_var twice" {
+	-re -wrap " = ($::decimal)" {
+	    set val2 $expect_out(1,string)
+	    pass "$gdb_test_name"
+	}
+    }
+
+    # The variable should have incremented.  (Note we didn't give it
+    # sufficient time to ever wrap around.)
+    gdb_assert {$val1 != $val2} "values are different"
+
+    set wp_str [expr ($hw)?"Hardware watchpoint":"Watchpoint"]
+
+    # Now set a watchpoint, while the inferior is running.  Since
+    # we're watching a global, and we can read global memory while the
+    # target is running, this should be able to work.
+    gdb_test_multiple "watch global_var" "" {
+	-re "$wp_str $::decimal: global_var\r\n$::gdb_prompt " {
+	    pass $gdb_test_name
+	}
+    }
+
+    # Check that the watchpoint triggers.
+
+    save_vars ::timeout {
+	if {!$hw} {
+	    # This doesn't currently work with software watchpoints.
+	    # GDB should transparently temporarily pause the inferior,
+	    # to force it to single step, but it doesn't, so the
+	    # thread continues running free.
+	    setup_kfail gdb/111111 *-*-*
+
+	    # No point waiting too much for output we know isn't
+	    # coming.
+	    set ::timeout 1
+	}
+	set re [multi_line \
+		    "$wp_str $::decimal: global_var" \
+		    "" \
+		    "Old value = $::decimal" \
+		    "New value = $::decimal"]
+	gdb_test_multiple "" "watchpoint hit" {
+	    -re $re {
+		pass $gdb_test_name
+	    }
+	}
+    }
+}
+
+foreach hw {0 1} {
+    if {!$allow_hw_watchpoint_tests_p} {
+	continue
+    }
+    foreach stop_mode {all-stop non-stop} {
+	set wp_type [expr ($hw)?"hardware":"software"]
+	with_test_prefix "$stop_mode: $wp_type" {
+	    test $stop_mode $hw
+	}
+    }
+}