From 43fac2962877de41284e8add5865245cbbe36da3 Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Thu, 17 Nov 2022 18:25:36 +0000 Subject: Make follow_fork not rely on get_last_target_status Currently, if - you're in all-stop mode, - the inferior last stopped because of a fork catchpoint, when you next resume the program, gdb checks whether it had last stopped for a fork/vfork, and if so, a) if the current thread is the one that forked, gdb follows the parent/child, depending on "set follow-fork" mode. b) if the current thread is some other thread (because you switched threads meanwhile), gdb switches back to that thread, gdb follows the parent/child, and stops the resumption command. There's a problem in b), however -- if you have "set schedule-multiple off", which is the default, or "set scheduler-locking on", gdb will still switch back to the forking thread, even if you didn't want to resume it. For example, with: (gdb) catch fork (gdb) c * thread 1 stops for fork (gdb) thread 2 (gdb) set scheduler-locking on (gdb) c gdb switches back to thread 1, and follows the fork. Or with: (gdb) add-inferior -exec prog (gdb) inferior 2 (gdb) start (gdb) inferior 1 (gdb) catch fork (gdb) c * thread 1.1 stops for fork (gdb) inferior 2 (gdb) set schedule-multiple off # this is the default (gdb) c gdb switches back to thread 1.1, and follows the fork. Another issue is that, because follow_fork relies on get_last_target_status to find the thread that has a pending fork, it is possible to confuse it. For example, "run" or "start" call init_wait_for_inferior, which clears the last target status, so this: (gdb) catch fork (gdb) c * thread 1 stops for fork (gdb) add-inferior -exec prog (gdb) inferior 2 (gdb) start (gdb) set follow-fork child (gdb) inferior 1 (gdb) n ... does not follow to the fork child of inferior 1, because the get_last_target_status call in follow_fork doesn't return a TARGET_WAITKIND_FORKED. Thanks to Simon for this example. All of the above are fixed by this patch. It changes follow_fork to not look at get_last_target_status, but to instead iterate over the set of threads that the user is resuming, and find the one that has a pending_follow kind of fork/vfork. gdb.base/foll-fork.exp is augmented to exercise the last "start" scenario described above. The other cases will be exercised in the testcase added by the following patch. Change-Id: Ifcca77e7b2456277387f40660ef06cec2b93b97e --- gdb/infrun.c | 67 ++++++++++++++++++++---------------- gdb/testsuite/gdb.base/foll-fork.exp | 36 +++++++++++++++++-- 2 files changed, 71 insertions(+), 32 deletions(-) diff --git a/gdb/infrun.c b/gdb/infrun.c index 252f6e5..617b630 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -705,6 +705,15 @@ holding the child stopped. Try \"set detach-on-fork\" or \ return false; } +/* Set the last target status as TP having stopped. */ + +static void +set_last_target_status_stopped (thread_info *tp) +{ + set_last_target_status (tp->inf->process_target (), tp->ptid, + target_waitstatus {}.set_stopped (GDB_SIGNAL_0)); +} + /* Tell the target to follow the fork we're stopped at. Returns true if the inferior should be resumed; false, if the target for some reason decided it's best not to resume. */ @@ -729,32 +738,33 @@ follow_fork () if (!non_stop) { - process_stratum_target *wait_target; - ptid_t wait_ptid; - struct target_waitstatus wait_status; + thread_info *cur_thr = inferior_thread (); - /* Get the last target status returned by target_wait(). */ - get_last_target_status (&wait_target, &wait_ptid, &wait_status); - - /* If not stopped at a fork event, then there's nothing else to - do. */ - if (wait_status.kind () != TARGET_WAITKIND_FORKED - && wait_status.kind () != TARGET_WAITKIND_VFORKED) - return 1; + ptid_t resume_ptid + = user_visible_resume_ptid (cur_thr->control.stepping_command); + process_stratum_target *resume_target + = user_visible_resume_target (resume_ptid); - /* Check if we switched over from WAIT_PTID, since the event was - reported. */ - if (wait_ptid != minus_one_ptid - && (current_inferior ()->process_target () != wait_target - || inferior_ptid != wait_ptid)) + /* Check if there's a thread that we're about to resume, other + than the current, with an unfollowed fork/vfork. If so, + switch back to it, to tell the target to follow it (in either + direction). We'll afterwards refuse to resume, and inform + the user what happened. */ + for (thread_info *tp : all_non_exited_threads (resume_target, + resume_ptid)) { - /* We did. Switch back to WAIT_PTID thread, to tell the - target to follow it (in either direction). We'll - afterwards refuse to resume, and inform the user what - happened. */ - thread_info *wait_thread = find_thread_ptid (wait_target, wait_ptid); - switch_to_thread (wait_thread); - should_resume = false; + if (tp == cur_thr) + continue; + + if (tp->pending_follow.kind () != TARGET_WAITKIND_SPURIOUS) + { + infrun_debug_printf ("need to follow-fork [%s] first", + tp->ptid.to_string ().c_str ()); + + switch_to_thread (tp); + should_resume = false; + break; + } } } @@ -818,21 +828,16 @@ follow_fork () } else { - /* This makes sure we don't try to apply the "Switched - over from WAIT_PID" logic above. */ - nullify_last_target_wait_ptid (); - /* If we followed the child, switch to it... */ if (follow_child) { - thread_info *child_thr = find_thread_ptid (parent_targ, child); - switch_to_thread (child_thr); + tp = find_thread_ptid (parent_targ, child); + switch_to_thread (tp); /* ... and preserve the stepping state, in case the user was stepping over the fork call. */ if (should_resume) { - tp = inferior_thread (); tp->control.step_resume_breakpoint = step_resume_breakpoint; tp->control.step_range_start = step_range_start; @@ -871,6 +876,8 @@ follow_fork () break; } + if (!should_resume) + set_last_target_status_stopped (tp); return should_resume; } diff --git a/gdb/testsuite/gdb.base/foll-fork.exp b/gdb/testsuite/gdb.base/foll-fork.exp index 0ab2290..885c791 100644 --- a/gdb/testsuite/gdb.base/foll-fork.exp +++ b/gdb/testsuite/gdb.base/foll-fork.exp @@ -212,15 +212,22 @@ set reading_in_symbols_re {(?:\r\nReading in symbols for [^\r\n]*)?} # Test the ability to catch a fork, specify that the child be # followed, and continue. Make the catchpoint permanent. -proc_with_prefix catch_fork_child_follow {} { +proc_with_prefix catch_fork_child_follow {second_inferior} { global gdb_prompt global srcfile global reading_in_symbols_re + if { $second_inferior && [use_gdb_stub] } { + return + } + if { ![setup] } { return } + # Get rid of the breakpoint at "main". + delete_breakpoints + set bp_after_fork [gdb_get_line_number "set breakpoint here"] gdb_test "catch fork" \ @@ -249,6 +256,29 @@ proc_with_prefix catch_fork_child_follow {} { "Temporary breakpoint.*, line $bp_after_fork.*" \ "set follow-fork child, tbreak" + if {$second_inferior} { + gdb_test "add-inferior" "Added inferior 2.*" "add inferior 2" + + gdb_test "inferior 2" "Switching to inferior 2.*" + + gdb_load $::binfile + + # Start it. This should not affect inferior 1, given "set + # schedule-multiple off" (default). GDB used to have a bug + # where "start" would clear the pending follow fork + # information of inferior 1. + gdb_test "start" "Starting program.*Temporary breakpoint .*" + + gdb_test "inferior 1" "Switching to inferior 1.*" + + # Verify that the catchpoint is still mentioned in an "info + # breakpoints", and further that the catchpoint still shows + # the captured process id. + gdb_test "info breakpoints" \ + ".*catchpoint.*keep y.*fork, process.*" \ + "info breakpoints, after starting second inferior" + } + set expected_re "\\\[Attaching after.* fork to.*\\\[Detaching after fork from" append expected_re ".* at .*$bp_after_fork.*" gdb_test "continue" $expected_re "set follow-fork child, hit tbreak" @@ -431,6 +461,8 @@ foreach_with_prefix follow-fork-mode {"parent" "child"} { # Catchpoint tests. -catch_fork_child_follow +foreach_with_prefix second_inferior {false true} { + catch_fork_child_follow $second_inferior +} catch_fork_unpatch_child tcatch_fork_parent_follow -- cgit v1.1