gdb/testsuite/gdb.threads/attach-slow-waitpid.exp

# 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
# 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 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*] } {
    continue
}

standard_testfile

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"
	}

	gdb_start
    }
}

# 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"

gdb_exit

# Kill of test program.
kill_wait_spawned_process $test_spawn_id