From e95a97d41a186ac65077ba3103dc10e5d41fe7b5 Mon Sep 17 00:00:00 2001 From: Andreas Arnez Date: Wed, 7 Mar 2018 14:29:19 +0100 Subject: [PATCH] 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. --- 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(-) create mode 100644 gdb/testsuite/gdb.cp/watch-cp.cc create mode 100644 gdb/testsuite/gdb.cp/watch-cp.exp 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 + + * 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 * 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 + + * gdb.cp/watch-cp.cc: New test. + * gdb.cp/watch-cp.exp: New file. + 2018-03-06 Andrew Burgess * 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 . */ + +/* 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 . + +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\\}.*" -- 2.7.4