[PATCH 3/8] Deliver signal in hardware single step

[Yao Qi <qiyaoltc@gmail.com>]

GDBserver doesn't deliver signal when stepping over a breakpoint even
hardware single step is used.  When GDBserver started to step over
(thread creation) breakpoint for mutlit-threaded debugging in 2002 [1],
GDBserver behaves this way.

This behaviour gets trouble on conditional breakpoints on branch to
self instruction like this,

   0x00000000004005b6 <+29>:	jmp    0x4005b6 <main+29>

and I set breakpoint

$(gdb) break branch-to-self.c:43 if counter > 3

and the variable counter will be set to 5 in SIGALRM signal handler.
Since GDBserver keeps stepping over breakpoint, the SIGALRM can never
be dequeued and delivered to the inferior, so the program can't stop.
The test can be found in gdb.base/branch-to-self.exp.

I can understand why does GDBserver queue signal for software single
step, but I can't figure out a reason we should queue signal for
hardware single step.  With this patch applied, GDBserver forward the
signal to inferior and the program can stop correctly.

[1] PATCH: Multithreaded debugging for gdbserver
    https://sourceware.org/ml/gdb-patches/2002-06/msg00157.html

gdb/gdbserver:

2016-03-04  Yao Qi  <yao.qi@linaro.org>

	* linux-low.c (LWP_SIGNAL_CAN_BE_DELIVERED): Don't deliver
	signal when stepping over breakpoint with software single
	step.
---
 gdb/gdbserver/linux-low.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index dcf58db..2330e67 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -4119,11 +4119,12 @@ single_step (struct lwp_info* lwp)
 }
 
 /* The signal can not be delivered to the inferior if we are trying to
-   reinsert a breakpoint or we're trying to finish a fast tracepoint
-   collect.  */
+   reinsert a breakpoint for software single step or we're trying to
+   finish a fast tracepoint collect.  */
 
-#define LWP_SIGNAL_CAN_BE_DELIVERED(LWP) \
-  !((LWP)->bp_reinsert != 0 || (LWP)->collecting_fast_tracepoint)
+#define LWP_SIGNAL_CAN_BE_DELIVERED(LWP)			\
+  !(((LWP)->bp_reinsert != 0 && can_software_single_step ())	\
+    || (LWP)->collecting_fast_tracepoint)
 
 /* Resume execution of LWP.  If STEP is nonzero, single-step it.  If
    SIGNAL is nonzero, give it that signal.  */
-- 
1.9.1