binutils-gdb/gdb/testsuite/gdb.base/watch-bitfields.exp

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Fix PR12526: -location watchpoints for bitfield arguments PR 12526 reports that -location watchpoints against bitfield arguments trigger false positives when bits around the bitfield, but not the bitfield itself, are modified. This happens because -location watchpoints naturally operate at the byte level, not at the bit level. When the address of a bitfield lvalue is taken, information about the bitfield (i.e. its offset and size) is lost in the process. This information must first be retained throughout the lifetime of the -location watchpoint. This patch achieves this by adding two new fields to the watchpoint struct: val_bitpos and val_bitsize. These fields are set when a watchpoint is first defined in watch_command_1. They are both equal to zero if the watchpoint is not a -location watchpoint or if the argument is not a bitfield. Then these bitfield parameters are used inside update_watchpoint and watchpoint_check to extract the actual value of the bitfield from the watchpoint address, with the help of a local helper function extract_bitfield_from_watchpoint_value. Finally when creating a HW breakpoint pointing to a bitfield, we optimize the address and length of the breakpoint. By skipping over the bytes that don't cover the bitfield, this step reduces the frequency at which a read watchpoint for the bitfield is triggered. It also reduces the number of times a false-positive call to check_watchpoint is triggered for a write watchpoint. gdb/ PR breakpoints/12526 * breakpoint.h (struct watchpoint): New fields val_bitpos and val_bitsize. * breakpoint.c (watch_command_1): Use these fields to retain bitfield information. (extract_bitfield_from_watchpoint_value): New function. (watchpoint_check): Use it. (update_watchpoint): Use it. Optimize the address and length of a HW watchpoint pointing to a bitfield. * value.h (unpack_value_bitfield): New prototype. * value.c (unpack_value_bitfield): Make extern. gdb/testsuite/ PR breakpoints/12526 * gdb.base/watch-bitfields.exp: New file. * gdb.base/watch-bitfields.c: New file.
2014-09-16 18:40:06 +02:00
# Copyright 2014 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 file is part of the gdb testsuite
standard_testfile
if {[prepare_for_testing $testfile.exp $testfile $srcfile debug]} {
return -1
}
if {![runto_main]} {
return -1
}
# Continue inferior execution, expecting the watchpoint EXPR to be triggered
# having old value OLD and new value NEW.
proc expect_watchpoint { expr old new } {
set expr_re [string_to_regexp $expr]
gdb_test "print $expr" "\\$\\d+ = $old\\s"
gdb_test "cont" "$expr_re\\s.*Old value = $old\\s+New value = $new\\s.*"
gdb_test "print $expr" "\\$\\d+ = $new\\s"
}
# Check that -location watchpoints against bitfields trigger properly.
gdb_test "watch -l q.a"
gdb_test "watch -l q.e"
expect_watchpoint "q.a" 0 1
expect_watchpoint "q.e" 0 5
expect_watchpoint "q.a" 1 0
expect_watchpoint "q.e" 5 4
gdb_test "cont" ".*exited normally.*"
# Check that regular watchpoints against expressions involving bitfields
# trigger properly.
runto_main
gdb_test "watch q.d + q.f + q.g"
expect_watchpoint "q.d + q.f + q.g" 0 4
expect_watchpoint "q.d + q.f + q.g" 4 10
expect_watchpoint "q.d + q.f + q.g" 10 3
expect_watchpoint "q.d + q.f + q.g" 3 2
expect_watchpoint "q.d + q.f + q.g" 2 1
expect_watchpoint "q.d + q.f + q.g" 1 0
gdb_test "cont" ".*exited normally.*"