From c4d9ceb6473237e614c66be97351109b9f260505 Mon Sep 17 00:00:00 2001 From: Yao Qi Date: Fri, 12 Sep 2014 13:35:11 +0800 Subject: [PATCH] Honour SIGILL and SIGSEGV in cancel breakpoint and event lwp selection I see the following fail on arm-none-linux-gnueabi testing, (gdb) continue^M Continuing.^M ^M Program received signal SIGILL, Illegal instruction.^M [Switching to Thread 1003]^M handler (signo=10) at /scratch/yqi/arm-none-linux-gnueabi/src/gdb-trunk/gdb/testsuite/gdb.threads/sigstep-threads.c:33^M 33 tgkill (getpid (), gettid (), SIGUSR1); /* step-2 */^M (gdb) FAIL: gdb.threads/sigstep-threads.exp: continue the cause is that GDBserver doesn't cancel the breakpoint if the stop signal is SIGILL. The kernel used here is a little old, 2.6.x, and doesn't translate SIGILL to SIGTRAP when program hits breakpoint instruction (which is an illegal instruction actually). GDB and GDBserver can translate SIGILL to SIGTRAP under certain circumstance, so it is not a problem here. See gdbserver/linux-low.c:linux_wait_1 /* If this event was not handled before, and is not a SIGTRAP, we report it. SIGILL and SIGSEGV are also treated as traps in case a breakpoint is inserted at the current PC. If this target does not support internal breakpoints at all, we also report the SIGTRAP without further processing; it's of no concern to us. */ maybe_internal_trap = (supports_breakpoints () && (WSTOPSIG (w) == SIGTRAP || ((WSTOPSIG (w) == SIGILL || WSTOPSIG (w) == SIGSEGV) && (*the_low_target.breakpoint_at) (event_child->stop_pc)))); However, SIGILL and SIGSEGV is not considered when cancelling breakpoint, which causes the fail above. That is, when GDB is doing software single step on address ADDR, both thread A and thread B hits the software single step breakpoint, and get SIGILL. GDB selects the event from thread A, removes the software single step breakpoint, and resume the program. The event (SIGILL) from thread B is reported to GDB, but GDB doesn't regard this SIGILL as SIGTRAP, because the breakpoint on address ADDR was removed, so GDB reports "Program received signal SIGILL". The patch is to allow calling cancel_breakpoint if the signal is SIGILL and SIGSEGV. This patch fixes the fail above. Likewise, event lwp selection should honour SIGILL and SIGSEGV too. gdb/gdbserver: 2014-09-23 Yao Qi * linux-low.c (lp_status_maybe_breakpoint): New function. (linux_low_filter_event): Call lp_status_maybe_breakpoint. (count_events_callback): Likewise. (select_event_lwp_callback): Likewise. (cancel_breakpoints_callback): Likewise. --- gdb/gdbserver/ChangeLog | 8 ++++++++ gdb/gdbserver/linux-low.c | 28 ++++++++++++++++++---------- 2 files changed, 26 insertions(+), 10 deletions(-) diff --git a/gdb/gdbserver/ChangeLog b/gdb/gdbserver/ChangeLog index 240554ef882..a7efe8ef897 100644 --- a/gdb/gdbserver/ChangeLog +++ b/gdb/gdbserver/ChangeLog @@ -1,3 +1,11 @@ +2014-09-23 Yao Qi + + * linux-low.c (lp_status_maybe_breakpoint): New function. + (linux_low_filter_event): Call lp_status_maybe_breakpoint. + (count_events_callback): Likewise. + (select_event_lwp_callback): Likewise. + (cancel_breakpoints_callback): Likewise. + 2014-09-19 Don Breazeal * linux-low.c (handle_extended_wait): Call diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c index 8f0985a1394..8776670b496 100644 --- a/gdb/gdbserver/linux-low.c +++ b/gdb/gdbserver/linux-low.c @@ -1739,6 +1739,20 @@ cancel_breakpoint (struct lwp_info *lwp) return 0; } +/* Return true if the event in LP may be caused by breakpoint. */ + +static int +lp_status_maybe_breakpoint (struct lwp_info *lp) +{ + return (lp->status_pending_p + && WIFSTOPPED (lp->status_pending) + && (WSTOPSIG (lp->status_pending) == SIGTRAP + /* SIGILL and SIGSEGV are also treated as traps in case a + breakpoint is inserted at the current PC. */ + || WSTOPSIG (lp->status_pending) == SIGILL + || WSTOPSIG (lp->status_pending) == SIGSEGV)); +} + /* Do low-level handling of the event, and check if we should go on and pass it to caller code. Return the affected lwp if we are, or NULL otherwise. */ @@ -1936,7 +1950,7 @@ linux_low_filter_event (ptid_t filter_ptid, int lwpid, int wstat) the core before this one is handled. All-stop always cancels breakpoint hits in all threads. */ if (non_stop - && WSTOPSIG (wstat) == SIGTRAP + && lp_status_maybe_breakpoint (child) && cancel_breakpoint (child)) { /* Throw away the SIGTRAP. */ @@ -2197,9 +2211,7 @@ count_events_callback (struct inferior_list_entry *entry, void *data) should be reported to GDB. */ if (thread->last_status.kind == TARGET_WAITKIND_IGNORE && thread->last_resume_kind != resume_stop - && lp->status_pending_p - && WIFSTOPPED (lp->status_pending) - && WSTOPSIG (lp->status_pending) == SIGTRAP + && lp_status_maybe_breakpoint (lp) && !breakpoint_inserted_here (lp->stop_pc)) (*count)++; @@ -2237,9 +2249,7 @@ select_event_lwp_callback (struct inferior_list_entry *entry, void *data) /* Select only resumed LWPs that have a SIGTRAP event pending. */ if (thread->last_resume_kind != resume_stop && thread->last_status.kind == TARGET_WAITKIND_IGNORE - && lp->status_pending_p - && WIFSTOPPED (lp->status_pending) - && WSTOPSIG (lp->status_pending) == SIGTRAP + && lp_status_maybe_breakpoint (lp) && !breakpoint_inserted_here (lp->stop_pc)) if ((*selector)-- == 0) return 1; @@ -2271,9 +2281,7 @@ cancel_breakpoints_callback (struct inferior_list_entry *entry, void *data) if (thread->last_resume_kind != resume_stop && thread->last_status.kind == TARGET_WAITKIND_IGNORE - && lp->status_pending_p - && WIFSTOPPED (lp->status_pending) - && WSTOPSIG (lp->status_pending) == SIGTRAP + && lp_status_maybe_breakpoint (lp) && !lp->stepping && !lp->stopped_by_watchpoint && cancel_breakpoint (lp)) -- 2.30.2