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# Copyright 2018-2021 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
# 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 <>.
# This test script tries to expose a bug in some of the uses of
# waitpid in the Linux native support within GDB. The problem was
# spotted on systems which were heavily loaded when attaching to
# threaded test programs. What happened was that during the initial
# attach, the loop of waitpid calls that normally received the stop
# events from each of the threads in the inferior was not receiving a
# stop event for some threads (the kernel just hadn't sent the stop
# event yet).
# GDB would then trigger a call to stop_all_threads which would
# continue to wait for all of the outstanding threads to stop, when
# the outstanding stop events finally arrived GDB would then
# (incorrectly) discard the stop event, resume the thread, and
# continue to wait for the thread to stop.... which it now never
# would.
# In order to try and expose this issue reliably, this test preloads a
# library that intercepts waitpid calls. All waitpid calls targeting
# pid -1 with the WNOHANG flag are rate limited so that only 1 per
# second can complete. Additional calls are forced to return 0
# indicating no event waiting. This is enough to trigger the bug
# during the attach phase.
# This test only works on Linux
if { ![isnative] || [is_remote host] || [use_gdb_stub]
|| ![istarget *-linux*] } {
set libfile slow-waitpid
set libsrc "${srcdir}/${subdir}/${libfile}.c"
set libobj [standard_output_file ${libfile}.so]
with_test_prefix "compile preload library" {
# Compile the preload library. We only get away with this as we
# limit this test to running when ISNATIVE is true.
if { [gdb_compile_shlib_pthreads \
$libsrc $libobj {debug}] != "" } then {
return -1
with_test_prefix "compile test executable" {
# Compile the test program
if { [gdb_compile_pthreads \
"${srcdir}/${subdir}/${srcfile}" "${binfile}" \
executable {debug}] != "" } {
return -1
# Spawn GDB with LIB preloaded with LD_PRELOAD.
proc gdb_spawn_with_ld_preload {lib} {
global env
save_vars { env(LD_PRELOAD) } {
if { ![info exists env(LD_PRELOAD) ]
|| $env(LD_PRELOAD) == "" } {
set env(LD_PRELOAD) "$lib"
} else {
append env(LD_PRELOAD) ":$lib"
# Run test program in the background.
set test_spawn_id [spawn_wait_for_attach $binfile]
set testpid [spawn_id_get_pid $test_spawn_id]
# Start GDB with preload library in place.
if { [gdb_spawn_with_ld_preload $libobj] == -1 } {
# Make sure we get UNTESTED rather than UNRESOLVED.
set errcnt 0
untested "Couldn't start GDB with preloaded lib"
return -1
# Load binary, and attach to running program.
gdb_load ${binfile}
gdb_test "attach $testpid" "Attaching to program.*" "attach to target"
# Kill of test program.
kill_wait_spawned_process $test_spawn_id