From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 1551) id 0124D3858C52; Mon, 27 Feb 2023 19:14:42 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 0124D3858C52 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1677525282; bh=XURsR/BvqMnOjGEV8wWUGzcAGHLYelgCxyGylUiofms=; h=From:To:Subject:Date:From; b=a8zfI4FwCMaKwCNuALGMJDdHUMVlrcpF2WanPbIG55JwH/r1lQ7DwkKHT3C5rbFGN atyd13Zaan2eBOUfAhuqesBdOqcVKj4hYWQwbBoQaLqjNE8gEH860K77qRbvxVh2SW sS3xSmL07c5DuGNyCcDa9ddWh3fAMx+g1/5ZsBmI= Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable From: Pedro Alves To: gdb-cvs@sourceware.org Subject: [binutils-gdb] Make follow_fork not rely on get_last_target_status X-Act-Checkin: binutils-gdb X-Git-Author: Pedro Alves X-Git-Refname: refs/heads/master X-Git-Oldrev: 6bf09ec03d86fdea8476eb137025c701a85e6dec X-Git-Newrev: 3505d4c4f7e2156837c7bfcbecf0a03b202e7ffb Message-Id: <20230227191442.0124D3858C52@sourceware.org> Date: Mon, 27 Feb 2023 19:14:42 +0000 (GMT) List-Id: https://sourceware.org/git/gitweb.cgi?p=3Dbinutils-gdb.git;h=3D3505d4c4f7e2= 156837c7bfcbecf0a03b202e7ffb commit 3505d4c4f7e2156837c7bfcbecf0a03b202e7ffb Author: Pedro Alves Date: Thu Nov 17 18:25:36 2022 +0000 Make follow_fork not rely on get_last_target_status =20 Currently, if =20 - you're in all-stop mode, - the inferior last stopped because of a fork catchpoint, =20 when you next resume the program, gdb checks whether it had last stopped for a fork/vfork, and if so, =20 a) if the current thread is the one that forked, gdb follows the parent/child, depending on "set follow-fork" mode. =20 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. =20 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: =20 (gdb) catch fork (gdb) c * thread 1 stops for fork (gdb) thread 2 (gdb) set scheduler-locking on (gdb) c =20 gdb switches back to thread 1, and follows the fork. =20 Or with: =20 (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 =20 gdb switches back to thread 1.1, and follows the fork. =20 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: =20 (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 =20 ... 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. =20 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. =20 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. =20 Change-Id: Ifcca77e7b2456277387f40660ef06cec2b93b97e Diff: --- 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 05c824d2141..04d76895f5e 100644 --- a/gdb/infrun.c +++ b/gdb/infrun.c @@ -706,6 +706,15 @@ holding the child stopped. Try \"set detach-on-fork\"= or \ return false; } =20 +/* 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. */ @@ -730,32 +739,33 @@ follow_fork () =20 if (!non_stop) { - process_stratum_target *wait_target; - ptid_t wait_ptid; - struct target_waitstatus wait_status; + thread_info *cur_thr =3D inferior_thread (); =20 - /* 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 () !=3D TARGET_WAITKIND_FORKED - && wait_status.kind () !=3D TARGET_WAITKIND_VFORKED) - return 1; + ptid_t resume_ptid + =3D user_visible_resume_ptid (cur_thr->control.stepping_command); + process_stratum_target *resume_target + =3D user_visible_resume_target (resume_ptid); =20 - /* Check if we switched over from WAIT_PTID, since the event was - reported. */ - if (wait_ptid !=3D minus_one_ptid - && (current_inferior ()->process_target () !=3D wait_target - || inferior_ptid !=3D 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 =3D find_thread_ptid (wait_target, wait_ptid); - switch_to_thread (wait_thread); - should_resume =3D false; + if (tp =3D=3D cur_thr) + continue; + + if (tp->pending_follow.kind () !=3D TARGET_WAITKIND_SPURIOUS) + { + infrun_debug_printf ("need to follow-fork [%s] first", + tp->ptid.to_string ().c_str ()); + + switch_to_thread (tp); + should_resume =3D false; + break; + } } } =20 @@ -819,21 +829,16 @@ 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 =3D find_thread_ptid (parent_targ, child); - switch_to_thread (child_thr); + tp =3D find_thread_ptid (parent_targ, child); + switch_to_thread (tp); =20 /* ... and preserve the stepping state, in case the user was stepping over the fork call. */ if (should_resume) { - tp =3D inferior_thread (); tp->control.step_resume_breakpoint =3D step_resume_breakpoint; tp->control.step_range_start =3D step_range_start; @@ -872,6 +877,8 @@ follow_fork () break; } =20 + if (!should_resume) + set_last_target_status_stopped (tp); return should_resume; } =20 diff --git a/gdb/testsuite/gdb.base/foll-fork.exp b/gdb/testsuite/gdb.base/= foll-fork.exp index 51dfcce7ff5..df5dab056c2 100644 --- a/gdb/testsuite/gdb.base/foll-fork.exp +++ b/gdb/testsuite/gdb.base/foll-fork.exp @@ -209,15 +209,22 @@ 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. =20 -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 =20 + if { $second_inferior && [use_gdb_stub] } { + return + } + if { ![setup] } { return } =20 + # Get rid of the breakpoint at "main". + delete_breakpoints + set bp_after_fork [gdb_get_line_number "set breakpoint here"] =20 gdb_test "catch fork" \ @@ -246,6 +253,29 @@ proc_with_prefix catch_fork_child_follow {} { "Temporary breakpoint.*, line $bp_after_fork.*" \ "set follow-fork child, tbreak" =20 + if {$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 fo= rk from" append expected_re ".* at .*$bp_after_fork.*" gdb_test "continue" $expected_re "set follow-fork child, hit tbreak" @@ -428,6 +458,8 @@ foreach_with_prefix follow-fork-mode {"parent" "child"}= { =20 # Catchpoint tests. =20 -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