From 75b2eb97a49bf3b539d7e016b2d9a2339170a680 Mon Sep 17 00:00:00 2001 From: Andrew Burgess Date: Tue, 10 Oct 2023 10:17:35 +0100 Subject: [PATCH] gdb: call update_thread_list for $_inferior_thread_count function I noticed that sometimes the value returned by $_inferior_thread_count can become out of sync with the actual thread count of the inferior, and will disagree with the number of threads reported by 'info threads'. This commit fixes this issue. The cause of the problem is that 'info threads' includes a call to update_thread_list, this can be seen in print_thread_info_1 in thread.c, while $_inferior_thread_count doesn't include a similar call, see the function inferior_thread_count_make_value also in thread.c. Of course, this is only a problem when GDB is running on a target that relies on update_thread_list calls to learn about new threads, e.g. remote or extended-remote targets. Native targets generally learn about new threads as soon as they appear and will not have this problem. I ran into this issue when writing a test for the next commit which uses inferior function calls to add an remove threads from an inferior. But for testing I've made use of non-stop mode and asynchronous inferior execution; by reading the inferior state I can know when a new thread has been created, at which point I can print $_inferior_thread_count while the inferior is still running. This is important, if I stop the inferior then GDB will pass through an update_thread_list call in the normal stop code, which will synchronise the thread list, after which $_inferior_thread_count will report the correct value. With this change in place $_inferior_thread_count is now correct. --- gdb/testsuite/gdb.threads/inf-thr-count.c | 80 +++++++++ gdb/testsuite/gdb.threads/inf-thr-count.exp | 175 ++++++++++++++++++++ gdb/thread.c | 2 + 3 files changed, 257 insertions(+) create mode 100644 gdb/testsuite/gdb.threads/inf-thr-count.c create mode 100644 gdb/testsuite/gdb.threads/inf-thr-count.exp diff --git a/gdb/testsuite/gdb.threads/inf-thr-count.c b/gdb/testsuite/gdb.threads/inf-thr-count.c new file mode 100644 index 00000000000..48855041319 --- /dev/null +++ b/gdb/testsuite/gdb.threads/inf-thr-count.c @@ -0,0 +1,80 @@ +/* This testcase is part of GDB, the GNU debugger. + + Copyright 2023 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 . */ + +#include +#include +#include + +/* Set to 0 by GDB to cause the inferior to drop out of a spin loop. */ +volatile int spin = 1; + +/* Set by the inferior to communicate to GDB what stage of the test we are + in. Initially 0, but set to 1 once a new thread has been created. Then + set to 2 once the extra thread has exited. */ +volatile int stage = 0; + +/* New thread worker function. Just spins until GDB tells it to exit. */ +void * +thread_func (void *arg) +{ + assert (arg == NULL); + + stage = 1; + + while (spin) + sleep (1); + + return NULL; +} + +/* Somewhere to place a breakpoint. */ +void +breakpt () +{ + /* Nothing. */ +} + +/* Create a new test that spins until GDB tells it to exit. Then, once the + new thread has exited, this thread spins until GDB tells us to exit. */ +int +main () +{ + alarm (600); + + breakpt (); + + pthread_t thr; + int res; + + res = pthread_create (&thr, NULL, thread_func, NULL); + assert (res == 0); + + void *retval; + res = pthread_join (thr, &retval); + assert (res == 0); + + spin = 1; + stage = 2; + + while (spin) + sleep (1); + + breakpt (); + + return 0; +} + diff --git a/gdb/testsuite/gdb.threads/inf-thr-count.exp b/gdb/testsuite/gdb.threads/inf-thr-count.exp new file mode 100644 index 00000000000..8cfbf66d902 --- /dev/null +++ b/gdb/testsuite/gdb.threads/inf-thr-count.exp @@ -0,0 +1,175 @@ +# Copyright 2023 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 . + +# Check that the $_inferior_thread_count convenience variable will +# correctly update its value without passing through a normal stop +# event. +# +# When GDB is using a remote (or extended-remote) target, GDB only +# learns about changes to the thread list be explicitly querying the +# target. This is done as part of a normal stop, but there are some +# situations where the thread list can change, but GDB doesn't pass +# through a normal stop. +# +# For example, when the target is running asynchronously in non-stop +# mode; in this case GDB can query the thread list without the target +# ever stopping. +# +# Or after an inferior function call. +# +# The solution is to ensure that $_inferior_thread_count explicitly +# queries the target to update the thread list. This test checks that +# this is done. + +standard_testfile + +if {[build_executable "failed to prepare" $testfile $srcfile \ + {debug pthreads}] == -1} { + return -1 +} + +# Start GDB. Ensure we are in non-stop mode as we need to read from +# the inferior while it is running. +save_vars {GDBFLAGS} { + append GDBFLAGS " -ex \"set non-stop on\"" + clean_restart $binfile +} + +if ![runto_main] { + return -1 +} + +gdb_breakpoint breakpt +gdb_continue_to_breakpoint "first breakpt call" + +# Check we can see a single thread to begin with. +gdb_test "p \$_inferior_thread_count" \ + "^\\\$$::decimal = 1" \ + "only one thread in \$_inferior_thread_count" + +# We don't want thread events, it makes it harder to match GDB's +# output. +gdb_test_no_output "set print thread-events off" + +# Continue the program in the background. +set test "continue&" +gdb_test_multiple "continue&" $test { + -re "Continuing\\.\r\n$gdb_prompt " { + pass $test + } +} + +# Read the 'stage' flag from the inferior. This is initially 0, but +# will be set to 1 once the extra thread has been created, and then 2 +# once the extra thread has exited. +# +# We catch the case where we can't read from the inferior while the +# inferior is running, this happens if the target hasn't entered +# non-stop mode like we asked. In this case we interrupt the inferior +# and bail. +# +# Otherwise, if we can read from the inferior we try at most 10 times +# to read the flag (with a 1 second delay after each read). If the +# flag isn't set after this then we bail. The inferior is either very +# slow, or the thread hasn't started for some reason. +proc wait_for_stage { num } { + set failure_count 0 + set cmd "print /d stage" + set stage_flag 0 + gdb_test_multiple "$cmd" "wait for 'stage' flag to be $num" { + -re -wrap "^Cannot execute this command while the target is running\\.\r\nUse the \"interrupt\" command to stop the target\r\nand then try again\\." { + fail "$gdb_test_name (can't read asynchronously)" + gdb_test_no_output "interrupt" + + gdb_test_multiple "" "wait for thread to stop" { + -re "Thread .* received signal .*" { + pass $gdb_test_name + gdb_test "p 1 + 2" " = 3" + } + } + } + + -re -wrap "^\\$\[0-9\]* = (\[-\]*\[0-9\]*).*" { + set stage_flag $expect_out(1,string) + if {$stage_flag != $num} { + set stage_flag 0 + incr failure_count + if { $failure_count < 10 } { + sleep 1 + send_gdb "$cmd\n" + exp_continue + } + fail $gdb_test_name + } else { + pass $gdb_test_name + } + } + } + + return $stage_flag +} + +# Wait until we can see that the extra thread has been created. +if {![wait_for_stage 1]} { + unresolved "failed to see thread start" + return -1 +} + + +if {[target_info exists gdb_protocol] + && ([target_info gdb_protocol] == "remote" + || [target_info gdb_protocol] == "extended-remote")} { + set new_thread_re "\\\[New Thread \[^\r\n\]+\\\]\r\n" + set exit_thread_re "\\\[Thread \[^\r\n\]+ exited\\\]\r\n" +} else { + set new_thread_re "" + set exit_thread_re "" +} + +# This is the test we actually care about. Check that the +# $_inferior_thread_count convenience variable shows the correct +# thread count; the new thread should be visible. +gdb_test "with print thread-events on -- p \$_inferior_thread_count" \ + "^${new_thread_re}\\\$$::decimal = 2" \ + "second thread visible in \$_inferior_thread_count" + +# Set a variable in the inferior, this will cause the second thread to +# exit. +gdb_test_no_output "set variable spin = 0" \ + "set 'spin' flag to allow worker thread to exit" + +# Wait until the extra thread has exited. +if {![wait_for_stage 2]} { + unresolved "failed to see thread start" + return -1 +} + +# Check that the second thread has gone away. +gdb_test "with print thread-events on -- p \$_inferior_thread_count" \ + "^${exit_thread_re}\\\$$::decimal = 1" \ + "back to one thread visible in \$_inferior_thread_count" + +# Set a variable in the inferior, this will cause the second thread to +# exit. +gdb_test_no_output "set variable spin = 0" \ + "set 'spin' flag to allow main thread to exit" + +# When the second thread exits, the main thread joins with it, and +# then proceeds to hit the breakpt function again. +gdb_test_multiple "" "wait for main thread to stop" { + -re "Thread 1 \[^\r\n\]+ hit Breakpoint $decimal, breakpt \\(\\)\[^\r\n\]+\r\n\[^\r\n\]+\r\n" { + pass $gdb_test_name + } +} diff --git a/gdb/thread.c b/gdb/thread.c index c8145da59bc..0660589abbf 100644 --- a/gdb/thread.c +++ b/gdb/thread.c @@ -2183,6 +2183,8 @@ inferior_thread_count_make_value (struct gdbarch *gdbarch, { int int_val = 0; + update_thread_list (); + if (inferior_ptid != null_ptid) int_val = current_inferior ()->non_exited_threads ().size (); -- 2.30.2