old-cross-binutils/gdb/testsuite/gdb.threads/schedlock.exp
Pedro Alves 354204061c PR 17408 - assertion failure in switch_back_to_stepped_thread
This PR shows that GDB can easily trigger an assertion here, in
infrun.c:

 5392              /* Did we find the stepping thread?  */
 5393              if (tp->control.step_range_end)
 5394                {
 5395                  /* Yep.  There should only one though.  */
 5396                  gdb_assert (stepping_thread == NULL);
 5397
 5398                  /* The event thread is handled at the top, before we
 5399                     enter this loop.  */
 5400                  gdb_assert (tp != ecs->event_thread);
 5401
 5402                  /* If some thread other than the event thread is
 5403                     stepping, then scheduler locking can't be in effect,
 5404                     otherwise we wouldn't have resumed the current event
 5405                     thread in the first place.  */
 5406                  gdb_assert (!schedlock_applies (currently_stepping (tp)));
 5407
 5408                  stepping_thread = tp;
 5409                }

Like:

 gdb/infrun.c:5406: internal-error: switch_back_to_stepped_thread: Assertion `!schedlock_applies (1)' failed.

The way the assertion is written is assuming that with schedlock=step
we'll always leave threads other than the one with the stepping range
locked, while that's not true with the "next" command.  With schedlock
"step", other threads still run unlocked when "next" detects a
function call and steps over it.  Whether that makes sense or not,
still, it's documented that way in the manual.  If another thread hits
an event that doesn't cause a stop while the nexting thread steps over
a function call, we'll get here and fail the assertion.

The fix is just to adjust the assertion.  Even though we found the
stepping thread, we'll still step-over the breakpoint that just
triggered correctly.

Surprisingly, gdb.threads/schedlock.exp doesn't have any test that
steps over a function call.  This commits fixes that.  This ensures
that "next" doesn't switch focus to another thread, and checks whether
other threads run locked or not, depending on scheduler locking mode
and command.  There's a lot of duplication in that file that this ends
cleaning up.  There's more that could be cleaned up, but that would
end up an unrelated change, best done separately.

This new coverage in schedlock.exp happens to trigger the internal
error in question, like so:

 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: next to increment (1) (GDB internal error)
 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: next to increment (3) (GDB internal error)
 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: next to increment (5) (GDB internal error)
 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: next to increment (7) (GDB internal error)
 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: next to increment (9) (GDB internal error)
 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: next does not change thread (switched to thread 0)
 FAIL: gdb.threads/schedlock.exp: schedlock=step: cmd=next: call_function=1: current thread advanced - unlocked (wrong amount)

That's because we have more than one thread running the same loop, and
while one thread is stepping over a function call, the other thread
hits the step-resume breakpoint of the first, which needs to be
stepped over, and we end up in switch_back_to_stepped_thread exactly
in the problem case.

I think a simpler and more directed test is also useful, to not rely
on internal breakpoint magics.  So this commit also adds a test that
has a thread trip on a conditional breakpoint that doesn't cause a
user-visible stop while another thread is stepping over a call.  That
currently fails like this:

 FAIL: gdb.threads/next-bp-other-thread.exp: schedlock=step: next over function call (GDB internal error)

Tested on x86_64 Fedora 20.

gdb/
2014-10-29  Pedro Alves  <palves@redhat.com>

	PR gdb/17408
	* infrun.c (switch_back_to_stepped_thread): Use currently_stepping
	instead of assuming a thread with a stepping range is always
	stepping.

gdb/testsuite/
2014-10-29  Pedro Alves  <palves@redhat.com>

	PR gdb/17408
	* gdb.threads/schedlock.c (some_function): New function.
	(call_function): New global.
	(MAYBE_CALL_SOME_FUNCTION): New macro.
	(thread_function): Call it.
	* gdb.threads/schedlock.exp (get_args): Add description parameter,
	and use it instead of a global counter.  Adjust all callers.
	(get_current_thread): Use "find current thread" for test message
	here rather than having all callers pass down the same string.
	(goto_loop): New procedure, factored out from ...
	(my_continue): ... this.
	(step_ten_loops): Change parameter from test message to command to
	use.  Adjust.
	(list_count): Delete global.
	(check_result): New procedure, factored out from duplicate top
	level code.
	(continue tests): Wrap in with_test_prefix.
	(test_step): New procedure, factored out from duplicate top level
	code.
	(top level): Test "step" in combination with all scheduler-locking
	modes.  Test "next" in combination with all scheduler-locking
	modes, and in combination with stepping over a function call or
	not.
	* gdb.threads/next-bp-other-thread.c: New file.
	* gdb.threads/next-bp-other-thread.exp: New file.
2014-10-29 18:15:39 +00:00

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# Copyright (C) 1996-2014 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 was written by Daniel Jacobowitz <drow@mvista.com>
# (parts based on pthreads.exp by Fred Fish (fnf@cygnus.com).
#
# This test covers the various forms of "set scheduler-locking".
standard_testfile
# The number of threads, including the main thread.
set NUM 2
if {[gdb_compile_pthreads "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable debug] != "" } {
return -1
}
# Now we can proceed with the real testing.
# Get the current contents of the `args` array in the test program.
# Description is appended to the test message.
proc get_args { description } {
global gdb_prompt
global NUM
set pattern "(\[0-9\]+)"
for {set i 1} {[expr $i < $NUM]} {incr i} {
append pattern ", (\[0-9\]+)"
}
set test "listed args ($description)"
gdb_test_multiple "print args" $test {
-re "\\\$\[0-9\]+ = {$pattern}.*$gdb_prompt $" {
pass $test
set result ""
for {set i 1} {[expr $i <= $NUM]} {incr i} {
lappend result $expect_out($i,string)
}
return $result
}
}
}
proc stop_process { description } {
global gdb_prompt
# For this to work we must be sure to consume the "Continuing."
# message first, or GDB's signal handler may not be in place.
after 1000 {send_gdb "\003"}
gdb_expect {
-re "Program received signal SIGINT.*$gdb_prompt $"
{
pass $description
}
timeout
{
fail "$description (timeout)"
}
}
}
proc get_current_thread { description } {
global gdb_prompt
set test "find current thread ($description)"
gdb_test_multiple "bt" $test {
-re "thread_function \\(arg=0x(\[0-9\])\\).*$gdb_prompt $" {
pass $test
return $expect_out(1,string)
}
}
return ""
}
# Make sure we're stopped in the loop, in one of the non-main threads.
proc goto_loop { msg } {
gdb_breakpoint [concat [gdb_get_line_number "schedlock.exp: main loop"] " if arg != 0"]
set test "return to loop"
if {$msg != ""} {
set test "$test ($msg)"
}
gdb_continue_to_breakpoint $test
delete_breakpoints
}
proc my_continue { msg } {
set test "continue ($msg)"
gdb_test_multiple "continue" $test {
-re "Continuing" {
pass $test
}
}
stop_process "stop all threads ($msg)"
goto_loop $msg
}
# Use CMD to step the loop 10 times. CMD may be "step" or "next".
proc step_ten_loops { cmd } {
global gdb_prompt
for {set i 0} {[expr $i < 10]} {set i [expr $i + 1]} {
set other_step 0
set test "$cmd to increment ($i)"
gdb_test_multiple $cmd $test {
-re ".*myp\\) \\+\\+;\[\r\n\]+$gdb_prompt $" {
pass $test
}
-re "$gdb_prompt $" {
if {$other_step == 0} {
set other_step 1
send_gdb "$cmd\n"
exp_continue
} else {
fail $test
# FIXME cascade?
}
}
}
}
}
# Start with a fresh gdb.
gdb_exit
gdb_start
gdb_reinitialize_dir $srcdir/$subdir
# We'll need this when we send_gdb a ^C to GDB. Need to do it before we
# run the program and gdb starts saving and restoring tty states.
gdb_test "shell stty intr '^C'" ".*"
gdb_load ${binfile}
gdb_test_no_output "set print sevenbit-strings"
gdb_test_no_output "set width 0"
runto_main
# See if scheduler locking is available on this target.
global gdb_prompt
gdb_test_multiple "set scheduler-locking off" "scheduler locking set to none" {
-re "Target .* cannot support this command" {
unsupported "target does not support scheduler locking"
return
}
-re "$gdb_prompt $" {
pass "scheduler locking set to none"
}
timeout {
unsupported "target does not support scheduler locking (timeout)"
return
}
}
gdb_breakpoint [gdb_get_line_number "schedlock.exp: last thread start"]
gdb_continue_to_breakpoint "all threads started"
set start_args [get_args "before initial"]
# First make sure that all threads are alive.
my_continue "initial"
set cont_args [get_args "after initial"]
set bad 0
for {set i 0} {[expr $i < $NUM]} {set i [expr $i + 1]} {
if {[lindex $start_args $i] == [lindex $cont_args $i]} {
incr bad
}
}
if { $bad == 0 } {
pass "all threads alive"
} else {
fail "all threads alive ($bad/$NUM did not run)"
}
# Compare the previous thread and args with the current thread and
# args. Check that we didn't switch threads, and that the threads
# incremented their args counter the amounts expected. CMD is the
# command being tested. BEFORE_THREAD is the thread that was selected
# before the command was run. BEFORE_ARGS is the value of the
# thread's args before the command was run. LOCKED indicates whether
# we expect threads other than the selected thread remained locked.
proc check_result { cmd before_thread before_args locked } {
global NUM
# Make sure we're still in the same thread.
set newthread [get_current_thread "after"]
set test "$cmd does not change thread"
if {$before_thread == $newthread} {
pass "$test"
} else {
fail "$test (switched to thread $newthread)"
}
set after_args [get_args "after"]
set test "current thread advanced"
if { $locked } {
set test "$test - locked"
} else {
set test "$test - unlocked"
}
set num_other_threads 0
for {set i 0} {$i < $NUM} {incr i} {
if {[lindex $before_args $i] == [lindex $after_args $i]} {
if {$i == $before_thread} {
fail "$test (didn't run)"
}
} else {
if {$i == $before_thread} {
if {$cmd == "continue"
|| [lindex $before_args $i] == [expr [lindex $after_args $i] - 10]} {
pass "$test"
} else {
fail "$test (wrong amount)"
}
} else {
incr num_other_threads
}
}
}
if { $locked } {
gdb_assert {$num_other_threads == 0} "other threads didn't run - locked"
} else {
gdb_assert {$num_other_threads > 0} "other threads ran - unlocked"
}
}
with_test_prefix "schedlock=on: cmd=continue" {
# Use whichever we stopped in.
set curthread [get_current_thread "before"]
# Test continue with scheduler locking.
gdb_test "set scheduler-locking on" ""
my_continue "with lock"
check_result "continue" $curthread $cont_args 1
}
# Test stepping/nexting with different modes of scheduler locking.
proc test_step { schedlock cmd call_function } {
global NUM
gdb_test_no_output "set scheduler-locking off"
goto_loop ""
set curthread [get_current_thread "before"]
# No need to set to off again. This avoids a duplicate message.
if {$schedlock != "off"} {
gdb_test_no_output "set scheduler-locking $schedlock"
}
gdb_test "print call_function = $call_function" \
" = $call_function"
set before_args [get_args "before"]
step_ten_loops $cmd
# "next" lets other threads run while stepping over functions.
if { $schedlock == "on" || ($schedlock == "step" && !$call_function) } {
set locked 1
} else {
set locked 0
}
check_result $cmd $curthread $before_args $locked
}
# Test stepping/nexting with different modes of scheduler locking.
foreach schedlock {"off" "step" "on"} {
with_test_prefix "schedlock=$schedlock" {
with_test_prefix "cmd=step" {
test_step $schedlock "step" 0
}
with_test_prefix "cmd=next" {
# With "next", and schedlock "step", threads run unlocked
# when stepping over a function call. This exercises both
# with and without a function call. Without a function
# call "next" should behave just like "step".
foreach call_function {0 1} {
with_test_prefix "call_function=$call_function" {
test_step $schedlock "next" $call_function
}
}
}
}
}