gdb/testsuite/gdb.base/watchpoint-stops-at-right-insn.exp

# This testcase is part of GDB, the GNU debugger.

# Copyright 2014-2021 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.

# Test that GDB presents a hardware watchpoint stop at the first
# instruction right after the instruction that changes memory.
#
# Some targets trigger a hardware watchpoint after the instruction
# that wrote memory executes, thus with the memory already changed and
# the PC pointing to the instruction after the instruction that wrote
# to memory.  These targets are said to have "continuable"
# watchpoints, referring to the fact that to make progress after the
# watchpoint triggers, GDB just needs to continue the target.
#
# Other targets trigger a hardware watchpoint at the instruction which
# has attempted to write to the piece of memory under control of the
# watchpoint, with the instruction actually not executed yet.  To be
# able to check whether the watched value changed, GDB needs to
# complete the memory write, single-stepping the target once.  These
# targets are said to have "non-continuable" watchpoints.
#
# This test makes sure that GDB knows which kind of watchpoint the
# target has, using this sequence of steps:
#
# 1 - run to main
#
# 2 - set a software watchpoint
#
# 3 - continue until watchpoint triggers
#
# 4 - the PC now points to the instruction right after the instruction
#     that actually caused the memory write.  So this is the address a
#     hardware watchpoint should present the stop to the user too.
#     Store the PC address.
#
# 5 - replace the software watchpoint by a hardware watchpoint
#
# 6 - continue until hardware watchpoint triggers
#
# 7 - the PC must point to the same address the software watchpoint
#     triggered at.
#
# If the target has continuable watchpoints, but GDB thinks it has
# non-continuable watchpoints, GDB will stop the inferior two
# instructions after the watched value change, rather than at the next
# instruction.
#
# If the target has non-continuable watchpoints, while GDB thinks it
# has continuable watchpoints, GDB will see a watchpoint trigger,
# notice no value changed, and immediatly continue the target.  Now,
# either the target manages to step-over the watchpoint transparently,
# and GDB thus fails to present to value change to the user, or, the
# watchpoint will keep re-triggering, with the program never making
# any progress.

standard_testfile

# No use testing this if we can't use hardware watchpoints.
if {[target_info exists gdb,no_hardware_watchpoints]} {
    return -1
}

if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
    return -1
}

if { ![runto_main] } then {
    return
}

# Get the current PC.  TEST is used as test prefix.

proc get_pc {test} {
    global hex gdb_prompt

    set addr ""
    gdb_test_multiple "p /x \$pc" "$test" {
	-re " = ($hex).*$gdb_prompt $" {
	    set addr $expect_out(1,string)
	    pass "$test"
	}
    }

    return $addr
}

# So we get an immediate warning/error if the target doesn't support a
# given watchpoint type.
gdb_test_no_output "set breakpoint always-inserted on"

set hw_watchpoints_supported 0

set test "set probe hw watchpoint"
gdb_test_multiple "watch global" $test {
    -re "You may have requested too many.*$gdb_prompt $" {
	pass $test
    }
    -re "Target does not support.*$gdb_prompt $" {
	pass $test
    }
    -re "$gdb_prompt $" {
	pass $test
	set hw_watchpoints_supported 1
    }
}

if {!$hw_watchpoints_supported} {
    unsupported "no hw watchpoints support"
    return
}

delete_breakpoints

proc test {always_inserted} {
    global srcfile binfile

    with_test_prefix "always-inserted $always_inserted" {

	clean_restart $binfile

	if { ![runto_main] } then {
	    return
	}

	# Force use of software watchpoints.
	gdb_test_no_output "set can-use-hw-watchpoints 0"

	gdb_test "watch global" \
	    "Watchpoint .*: global" \
	    "set software watchpoint on global variable"

	gdb_test "continue" \
	    "Watchpoint .*: global.*Old value = 0.*New value = 1.*set_global \\(val=1\\).*$srcfile.*" \
	    "software watchpoint triggers"

	set sw_watch_pc [get_pc "get sw watchpoint PC"]

	delete_breakpoints

	# Allow hardware watchpoints again.
	gdb_test_no_output "set can-use-hw-watchpoints 1"

	gdb_test "watch global" \
	    "Hardware watchpoint .*: global" \
	    "set hardware watchpoint on global variable"

	gdb_test "continue" \
	    "Hardware watchpoint .*: global.*Old value = 1.*New value = 2.*set_global \\(val=2\\).*$srcfile.*" \
	    "hardware watchpoint triggers"

	set hw_watch_pc [get_pc "get hw watchpoint PC"]

	gdb_assert {$sw_watch_pc == $hw_watch_pc} "hw watchpoint stops at right instruction"
    }
}

foreach always_inserted {"off" "on" } {
    test $always_inserted
}