From 0f8288ae82bf5bdb33d46d7447cd3132393a1bd2 Mon Sep 17 00:00:00 2001 From: Yao Qi Date: Thu, 3 Mar 2016 09:17:44 +0000 Subject: [PATCH] [GDBserver] Leave child suspended when step over parent I see the following GDBserver internal error in two cases, gdb/gdbserver/linux-low.c:1922: A problem internal to GDBserver has been detected. unsuspend LWP 17200, suspended=-1 1. step over a breakpoint on fork/vfork syscall instruction, 2. step over a breakpoint on clone syscall instruction and child threads hits a breakpoint, the stack backtrace is #0 internal_error (file=file@entry=0x44c4c0 "gdb/gdbserver/linux-low.c", line=line@entry=1922, fmt=fmt@entry=0x44c7d0 "unsuspend LWP %ld, suspended=%d\n") at gdb/gdbserver/../common/errors.c:51 #1 0x0000000000424014 in lwp_suspended_decr (lwp=, lwp=) at gdb/gdbserver/linux-low.c:1922 #2 0x000000000042403a in unsuspend_one_lwp (entry=, except=0x66e8c0) at gdb/gdbserver/linux-low.c:2885 #3 0x0000000000405f45 in find_inferior (list=, func=func@entry=0x424020 , arg=arg@entry=0x66e8c0) at gdb/gdbserver/inferiors.c:243 #4 0x00000000004297de in unsuspend_all_lwps (except=0x66e8c0) at gdb/gdbserver/linux-low.c:2895 #5 linux_wait_1 (ptid=..., ourstatus=ourstatus@entry=0x665ec0 , target_options=target_options@entry=0) at gdb/gdbserver/linux-low.c:3632 #6 0x000000000042a764 in linux_wait (ptid=..., ourstatus=0x665ec0 , target_options=0) at gdb/gdbserver/linux-low.c:3770 #7 0x0000000000411163 in mywait (ptid=..., ourstatus=ourstatus@entry=0x665ec0 , options=options@entry=0, connected_wait=connected_wait@entry=1) at gdb/gdbserver/target.c:214 #8 0x000000000040b1f2 in resume (actions=0x66f800, num_actions=1) at gdb/gdbserver/server.c:2757 #9 0x000000000040f660 in handle_v_cont (own_buf=0x66a630 "vCont;c:p45e9.-1") at gdb/gdbserver/server.c:2719 when GDBserver steps over a thread, other threads have been suspended, the "stepping" thread may create new thread, but GDBserver doesn't set it suspend count to 1. When GDBserver unsuspend threads, the child's suspend count goes to -1, and the assert is triggered. In fact, GDBserver has already taken care of suspend count of new thread when GDBserver is suspending all threads except the one GDBserver wants to step over by https://sourceware.org/ml/gdb-patches/2015-07/msg00946.html + /* If we're suspending all threads, leave this one suspended + too. */ + if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS) + { + if (debug_threads) + debug_printf ("HEW: leaving child suspended\n"); + child_lwp->suspended = 1; + } but that is not enough, because new thread is still can be spawned in the thread which is being stepped over. This patch extends the condition that GDBserver set child's suspend count to one if it is suspending threads or stepping over the thread. gdb/gdbserver: 2016-03-03 Yao Qi PR server/19736 * linux-low.c (handle_extended_wait): Set child suspended if event_lwp->bp_reinsert isn't zero. --- gdb/gdbserver/ChangeLog | 6 ++++++ gdb/gdbserver/linux-low.c | 16 +++++++++++----- 2 files changed, 17 insertions(+), 5 deletions(-) diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 089ca32..6c23574 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,9 @@ +2016-03-03 Yao Qi + + PR server/19736 + * linux-low.c (handle_extended_wait): Set child suspended + if event_lwp->bp_reinsert isn't zero. + 2016-03-02 Yao Qi * linux-low.c (linux_resume_one_lwp_throw): Replace code with diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c index 22bf915..6b07c90 100644 --- a/gdb/gdbserver/linux-low.c +++ b/gdb/gdbserver/linux-low.c @@ -529,8 +529,11 @@ handle_extended_wait (struct lwp_info **orig_event_lwp, int wstat) child_thr->last_status.kind = TARGET_WAITKIND_STOPPED; /* If we're suspending all threads, leave this one suspended - too. */ - if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS) + too. If the fork/clone parent is stepping over a breakpoint, + all other threads have been suspended already. Leave the + child suspended too. */ + if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS + || event_lwp->bp_reinsert != 0) { if (debug_threads) debug_printf ("HEW: leaving child suspended\n"); @@ -583,9 +586,12 @@ handle_extended_wait (struct lwp_info **orig_event_lwp, int wstat) before calling linux_resume_one_lwp. */ new_lwp->stopped = 1; - /* If we're suspending all threads, leave this one suspended - too. */ - if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS) + /* If we're suspending all threads, leave this one suspended + too. If the fork/clone parent is stepping over a breakpoint, + all other threads have been suspended already. Leave the + child suspended too. */ + if (stopping_threads == STOPPING_AND_SUSPENDING_THREADS + || event_lwp->bp_reinsert != 0) new_lwp->suspended = 1; /* Normally we will get the pending SIGSTOP. But in some cases -- 2.7.4