From b6d8d612d30dcdfc8ba8edfb15b4cd1753b0b8a2 Mon Sep 17 00:00:00 2001 From: Kevin Buettner Date: Tue, 1 Aug 2023 13:33:24 -0700 Subject: [PATCH] gdbserver: Reinstall software single-step breakpoints in resume_stopped_resumed_lwps At the moment, while performing a software single-step, gdbserver fails to reinsert software single-step breakpoints for a LWP when interrupted by a signal in another thread. This commit fixes this problem by reinstalling software single-step breakpoints in linux_process_target::resume_stopped_resumed_lwps in gdbserver/linux-low.cc. This bug was discovered due to a failing assert in maybe_hw_step() in gdbserver/linux-low.cc. Looking at the backtrace revealed that the caller was linux_process_target::resume_stopped_resumed_lwps. I was uncertain whether the assert should still be valid when called from that method, so I tried hoisting the assert from maybe_hw_step to all callers except resume_stopped_resumed_lwps. But running the new test case, described below, showed that merely eliminating the assert for this case was NOT a good fix - a study of the log file for the test showed that the single-step operation failed to occur. Instead GDB (via gdbserver) stopped at the next breakpoint that was hit. Zhiyong Yan had proposed a fix which resinserted software single-step breakpoints, albeit at a different location in linux-low.cc. Testing revealed that, while running gdb.threads/pending-fork-event-detach, the executable associated with that test would die due to a SIGTRAP after the test program was detached. Examination of the core file(s) showed that a breakpoint instruction had been left in program memory. Test results were otherwise very good, so Zhiyong was definitely on the right track! This commit causes software single-step breakpoint(s) to be inserted before the call to maybe_hw_step in resume_stopped_resumed_lwps. This will cause 'has_single_step_breakpoints (thread)' to be true, so that the assert in maybe_hw_step... /* GDBserver must insert single-step breakpoint for software single step. */ gdb_assert (has_single_step_breakpoints (thread)); ...will no longer fail. And better still, the single-step breakpoints are reinstalled, so that stepping will actually work, even when interrupted. The C code for the test case was loosely adapted from the reproducer provided in Zhiyong's bug report for this problem. The .exp file was copied from next-fork-other-thread.exp and then tweaked slightly. As noted in a comment in next-fork-exec-other-thread.exp, I had to remove "on" from the loop for non-stop as it was failing on all architectures (including x86-64) that I tested. I have a feeling that it ought to work, but this can be investigated separately and (re)enabled once it works. I also increased the number of iterations for the loop running the "next" commands. I've had some test runs which don't show the bug until the loop counter exceeded 100 iterations. The C file for the new test uses shorter delays than next-fork-other-thread.c though, so it doesn't take overly long (IMO) to run this new test. Running the new test on a Raspberry Pi w/ a 32-bit (Arm) kernel and userland using a gdbserver build without the fix in this commit shows the following results: FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=fork: target-non-stop=auto: non-stop=off: displaced-stepping=auto: i=12: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=fork: target-non-stop=auto: non-stop=off: displaced-stepping=on: i=9: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=fork: target-non-stop=auto: non-stop=off: displaced-stepping=off: i=18: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=fork: target-non-stop=off: non-stop=off: displaced-stepping=auto: i=3: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=fork: target-non-stop=off: non-stop=off: displaced-stepping=on: i=11: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=fork: target-non-stop=off: non-stop=off: displaced-stepping=off: i=1: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=auto: non-stop=off: displaced-stepping=auto: i=1: next to break here FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=auto: non-stop=off: displaced-stepping=on: i=3: next to break here FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=auto: non-stop=off: displaced-stepping=off: i=1: next to break here FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=on: non-stop=off: displaced-stepping=auto: i=47: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=on: non-stop=off: displaced-stepping=on: i=57: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=off: non-stop=off: displaced-stepping=auto: i=1: next to break here FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=off: non-stop=off: displaced-stepping=on: i=10: next to break here FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=off: non-stop=off: displaced-stepping=off: i=1: next to break here === gdb Summary === # of unexpected core files 12 # of expected passes 3011 # of unexpected failures 14 Each of the 12 core files were caused by the failed assertion in maybe_hw_step in linux-low.c. These correspond to 12 of the unexpected failures. When the tests are run using a gdbserver build which includes the fix in this commit, the results are significantly better, but not perfect: FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=on: non-stop=off: displaced-stepping=auto: i=143: next to other line FAIL: gdb.threads/next-fork-exec-other-thread.exp: fork_func=vfork: target-non-stop=on: non-stop=off: displaced-stepping=on: i=25: next to other line === gdb Summary === # of expected passes 10178 # of unexpected failures 2 I think that the two remaining failures are due to some different problem. They are also racy - I've seen runs with no failures or only one failure, but never more than two. Also, those runs were conducted with the loop count in next-fork-exec-other-thread.exp set to 200. During his testing of this fix and the new test case, Luis Machado found that this test was taking a long time and asked about ways to speed it up. I then conducted additional tests in which I gradually reduced the loop count, timing each one, also noting the number of failures. With the loop count set to 30, I found that I could still reliably reproduce the failures that Zhiyong reported (in which, with the proper settings, core files are created). But, with the loop count set to 30, the other failures noted above were much less likely to show up. Anyone wishing to investigate those other failures should set the loop count back up to 200. Running the new test on x86-64 and aarch64, both native and native-gdbserver shows no failures. Also, I see no regressions when running the entire test suite for armv7l-unknown-linux-gnueabihf (i.e. the Raspberry Pi w/ 32-bit kernel+userland) with --target_board=native-gdbserver. Additionally, using --target_board=native-gdbserver, I also see no regressions for the entire test suite for x86-64 and aarch64 running Fedora 38. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30387 Co-Authored-By: Zhiyong Yan Tested-By: Zhiyong Yan Tested-By: Luis Machado --- .../gdb.threads/next-fork-exec-other-thread.c | 82 +++++++++++ .../next-fork-exec-other-thread.exp | 131 ++++++++++++++++++ gdbserver/linux-low.cc | 7 +- 3 files changed, 219 insertions(+), 1 deletion(-) create mode 100644 gdb/testsuite/gdb.threads/next-fork-exec-other-thread.c create mode 100644 gdb/testsuite/gdb.threads/next-fork-exec-other-thread.exp diff --git a/gdb/testsuite/gdb.threads/next-fork-exec-other-thread.c b/gdb/testsuite/gdb.threads/next-fork-exec-other-thread.c new file mode 100644 index 00000000000..884706c6c3c --- /dev/null +++ b/gdb/testsuite/gdb.threads/next-fork-exec-other-thread.c @@ -0,0 +1,82 @@ +/* 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 +#include +#include +#include +#include +#include + +#define MAX_LOOP_ITER 10000 + +static char *argv0; + +static void* +worker_a (void *pArg) +{ + int iter = 0; + char *args[] = {argv0, "self-call", NULL }; + + while (iter++ < MAX_LOOP_ITER) + { + pid_t pid = FORK_FUNC (); + if (pid == 0) + { + /* child */ + if (execvp (args[0], args) == -1) + { + fprintf (stderr, "execvp error: %d\n", errno); + exit (1); + } + } + + waitpid (pid, NULL, 0); + usleep (5); + } +} + +static void* +worker_b (void *pArg) +{ + int iter = 0; + while (iter++ < MAX_LOOP_ITER) /* for loop */ + { + usleep (5); /* break here */ + usleep (5); /* other line */ + } +} + +int +main (int argc, char **argv) +{ + pthread_t wa_pid; + pthread_t wb_pid; + + argv0 = argv[0]; + + if (argc > 1 && strcmp (argv[1], "self-call") == 0) + exit (0); + + pthread_create (&wa_pid, NULL, worker_a, NULL); + pthread_create (&wb_pid, NULL, worker_b, NULL); + pthread_join (wa_pid, NULL); + + exit (0); +} diff --git a/gdb/testsuite/gdb.threads/next-fork-exec-other-thread.exp b/gdb/testsuite/gdb.threads/next-fork-exec-other-thread.exp new file mode 100644 index 00000000000..5e0ac5b78df --- /dev/null +++ b/gdb/testsuite/gdb.threads/next-fork-exec-other-thread.exp @@ -0,0 +1,131 @@ +# Copyright 2022-2023 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 . + +# This test was adapted from next-fork-other-thread.exp. The .c file +# was adapted from the reproducer for this bug: +# +# https://sourceware.org/bugzilla/show_bug.cgi?id=30387# +# +# That bug demonstrates a problem with software-singlestep in gdbserver. +# Prior to being fixed, this test also demonstrated that bug for a +# 32-bit ARM target. (Use RUNTESTFLAGS="--target_board=native-gdbserver".) +# It has been reproduced on a Raspberry Pi running Ubunutu server +# 20.04.5 LTS with 32-bit kernel + 32-bit userland. It was NOT reproducible +# using a circa 2023 Raspberry Pi OS w/ 64-bit kernel and 32-bit userland. + +standard_testfile + +# Line where to stop the main thread. +set break_here_line [gdb_get_line_number "break here"] + +# Build executables, one for each fork flavor. +foreach_with_prefix fork_func {fork vfork} { + set opts [list debug pthreads additional_flags=-DFORK_FUNC=${fork_func}] + if { [build_executable "failed to prepare" \ + ${testfile}-${fork_func} ${srcfile} $opts] } { + return + } +} + +# If testing against GDBserver, consume all it its output. + +proc drain_gdbserver_output { } { + if { [info exists ::server_spawn_id] } { + gdb_test_multiple "" "" { + -i "$::server_spawn_id" + -timeout 0 + -re ".+" { + exp_continue + } + } + } +} + +# Run the test with the given parameters: +# +# - FORK_FUNC: fork flavor, "fork" or "vfork". +# - TARGET-NON-STOP: "maintenance set target-non-stop" value, "auto", "on" or +# "off". +# - NON-STOP: "set non-stop" value, "on" or "off". +# - DISPLACED-STEPPING: "set displaced-stepping" value, "auto", "on" or "off". + +proc do_test { fork_func target-non-stop non-stop displaced-stepping } { + save_vars { ::GDBFLAGS } { + append ::GDBFLAGS " -ex \"maintenance set target-non-stop ${target-non-stop}\"" + append ::GDBFLAGS " -ex \"set non-stop ${non-stop}\"" + clean_restart ${::binfile}-${fork_func} + } + + gdb_test_no_output "set displaced-stepping ${displaced-stepping}" + + if { ![runto_main] } { + return + } + + # The "Detached after (v)fork" messages get in the way in non-stop, disable + # them. + gdb_test_no_output "set print inferior-events off" + + # Advance the next-ing thread to the point where we'll execute the nexts. + # Leave the breakpoint in: it will force GDB to step over it while next-ing, + # which exercises some additional code paths. + gdb_test "break $::break_here_line" "Breakpoint $::decimal at $::hex.*" + gdb_test "continue" "hit Breakpoint $::decimal, worker_b.*" + + # Next an arbitrary number of times over the lines of the loop. + for { set i 0 } { $i < 30 } { incr i } { + # If testing against GDBserver, the forking threads cause a lot of + # "Detaching from process XYZ" messages to appear. If we don't consume + # that output, GDBserver eventually blocks on a full stderr. Drain it + # once every loop. It may not be needed for 20 iterations, but it's + # needed if you increase to 200 iterations. + drain_gdbserver_output + + with_test_prefix "i=$i" { + if { [gdb_test "next" "other line.*" "next to other line"] != 0 } { + return + } + + if { [gdb_test "next" "for loop.*" "next to for loop"] != 0 } { + return + } + + if { [gdb_test "next" "break here.*" "next to break here"] != 0} { + return + } + } + } +} + +foreach_with_prefix fork_func {fork vfork} { + foreach_with_prefix target-non-stop {auto on off} { + # This file was copied from next-fork-other-thread.exp and + # then adapted for the a case which also involves an exec in + # addition to the fork. Ideally, we should test non-stop "on" + # in addition to "off", but, for this test, that results in a + # number of failures occur preceded by the message: + # + # Cannot execute this command while the selected thread is running. + # + # That seems like correct behavior to me, but perhaps the + # non-stop case can be made to work; if so, simply add "on" + # after "off" on the line below... + foreach_with_prefix non-stop {off} { + foreach_with_prefix displaced-stepping {auto on off} { + do_test ${fork_func} ${target-non-stop} ${non-stop} ${displaced-stepping} + } + } + } +} diff --git a/gdbserver/linux-low.cc b/gdbserver/linux-low.cc index 651f219b738..e1806ade82f 100644 --- a/gdbserver/linux-low.cc +++ b/gdbserver/linux-low.cc @@ -2463,7 +2463,12 @@ linux_process_target::resume_stopped_resumed_lwps (thread_info *thread) int step = 0; if (thread->last_resume_kind == resume_step) - step = maybe_hw_step (thread); + { + if (supports_software_single_step ()) + install_software_single_step_breakpoints (lp); + + step = maybe_hw_step (thread); + } threads_debug_printf ("resuming stopped-resumed LWP %s at %s: step=%d", target_pid_to_str (ptid_of (thread)).c_str (), -- 2.30.2