This is the mail archive of the gdb-cvs@sourceware.org mailing list for the GDB project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[binutils-gdb] Fix watching structs in C++


https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=e95a97d41a186ac65077ba3103dc10e5d41fe7b5

commit e95a97d41a186ac65077ba3103dc10e5d41fe7b5
Author: Andreas Arnez <arnez@linux.vnet.ibm.com>
Date:   Wed Mar 7 14:29:19 2018 +0100

    Fix watching structs in C++
    
    Some of the watchpoint logic depends on the fact that the head of the
    value chain represents the user-specified value to watch.  Thus no
    additional values should be added to the value chain after that.  However,
    if a watchpoint is defined for a C++ structure/class object, then run-time
    type information (RTTI) may be present.  Thus, while constructing the
    value chain for the watchpoint, the dynamic type is fetched by
    gnuv3_rrti_type, which invokes value_addr, which then adds a new value to
    the head of the value chain.  This new value represents the pointer to the
    structure instead of the structure itself.
    
    With such a "polluted" value chain the watchpoint logic does not recognize
    when the user intended to watch a struct, and can_use_hardware_watchpoint
    returns zero.  Instead of a hardware watchpoint, a software watchpoint
    will then be set for no apparent reason.
    
    This is fixed by adding an early exit to gnuv3_rtti_type when the input
    value is not a dynamic class object.
    
    gdb/testsuite/ChangeLog:
    
    	* gdb.cp/watch-cp.cc: New test.
    	* gdb.cp/watch-cp.exp: New file.
    
    gdb/ChangeLog:
    
    	* gnu-v3-abi.c (gnuv3_rtti_type): Add early exit if the given
    	value is not a dynamic class object.

Diff:
---
 gdb/ChangeLog                     |  5 +++++
 gdb/gnu-v3-abi.c                  |  5 +++--
 gdb/testsuite/ChangeLog           |  5 +++++
 gdb/testsuite/gdb.cp/watch-cp.cc  | 28 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.cp/watch-cp.exp | 35 +++++++++++++++++++++++++++++++++++
 5 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index a01206a..8de20e6 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-03-07  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
+	* gnu-v3-abi.c (gnuv3_rtti_type): Add early exit if the given
+	value is not a dynamic class object.
+
 2018-03-06  Tom Tromey  <tom@tromey.com>
 
 	* rust-exp.y: Formatting fixes.
diff --git a/gdb/gnu-v3-abi.c b/gdb/gnu-v3-abi.c
index 0965846..859187f 100644
--- a/gdb/gnu-v3-abi.c
+++ b/gdb/gnu-v3-abi.c
@@ -299,8 +299,9 @@ gnuv3_rtti_type (struct value *value,
   LONGEST offset_to_top;
   const char *atsign;
 
-  /* We only have RTTI for class objects.  */
-  if (TYPE_CODE (values_type) != TYPE_CODE_STRUCT)
+  /* We only have RTTI for dynamic class objects.  */
+  if (TYPE_CODE (values_type) != TYPE_CODE_STRUCT
+      || !gnuv3_dynamic_class (values_type))
     return NULL;
 
   /* Determine architecture.  */
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index b775102..e177884 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2018-03-07  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
+	* gdb.cp/watch-cp.cc: New test.
+	* gdb.cp/watch-cp.exp: New file.
+
 2018-03-06  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb.base/infcall-nested-structs.exp: New file.
diff --git a/gdb/testsuite/gdb.cp/watch-cp.cc b/gdb/testsuite/gdb.cp/watch-cp.cc
new file mode 100644
index 0000000..6954e85
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/watch-cp.cc
@@ -0,0 +1,28 @@
+/* Copyright 2018 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/>.  */
+
+/* A class that does not have RTTI and is small enough to fit in a
+   hardware watchpoint on all targets.  */
+class smallstuff { public: int n; };
+
+smallstuff watchme[5];
+
+int
+main ()
+{
+  for (int i = 0; i < sizeof (watchme) / sizeof (watchme[0]); i++)
+    watchme[i].n = i;
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.cp/watch-cp.exp b/gdb/testsuite/gdb.cp/watch-cp.exp
new file mode 100644
index 0000000..bdf0f13
--- /dev/null
+++ b/gdb/testsuite/gdb.cp/watch-cp.exp
@@ -0,0 +1,35 @@
+# Copyright 2018 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/>.
+
+if { [skip_cplus_tests] || [skip_hw_watchpoint_tests]} { continue }
+
+standard_testfile .cc
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug c++}]} {
+    return -1
+}
+
+if ![runto_main] then {
+    perror "couldn't run to main"
+    continue
+}
+
+gdb_test "watch watchme\[3\]" "atchpoint .*: watchme.*" "set watchpoint"
+
+# Verify that a hardware watchpoint is used.
+gdb_test "info watchpoints" " hw watchpoint .* watchme.*"
+
+# Now see whether it actually works.
+gdb_test "continue" "Hardware watchpoint .*New value = \\{n = 3\\}.*"


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]