Force to insert software single step breakpoint

GDB doesn't insert software single step breakpoint if the instruction
branches to itself, so that the program can't stop after command "si".

(gdb) b 32
Breakpoint 2 at 0x8680: file git/gdb/testsuite/gdb.base/branch-to-self.c, line 32.
(gdb) c
Continuing.

Breakpoint 2, main () at gdb/git/gdb/testsuite/gdb.base/branch-to-self.c:32
32	  asm (".Lhere: " BRANCH_INSN " .Lhere"); /* loop-line */
(gdb) si
infrun: clear_proceed_status_thread (Thread 3991.3991)
infrun: proceed (addr=0xffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: step-over queue now empty
infrun: resuming [Thread 3991.3991] for step-over
infrun: skipping breakpoint: stepping past insn at: 0x8680
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sending packet: $Z0,8678,4#f3...Packet received: OK
infrun: skipping breakpoint: stepping past insn at: 0x8680
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sending packet: $Z0,b6fe86c8,4#82...Packet received: OK
infrun: resume (step=1, signal=GDB_SIGNAL_0), trap_expected=1, current thread [Thread 3991.3991] at 0x868

breakpoint.c:should_be_inserted thinks the breakpoint shouldn't be
inserted, which is wrong.  This patch restrict the condition that
only skip the non-single-step breakpoints if they are inserted at
the place we are stepping over, however we don't want to skip
single-step breakpoint if its thread is the thread we are stepping
over, so in this patch, I add a thread num in 'struct step_over_info'
to record the thread we're stepping over.

gdb:

2016-04-25  Yao Qi  <yao.qi@linaro.org>

	* breakpoint.c (should_be_inserted): Return 0 if the location's
	owner is not single step breakpoint or single step breakpoint's
	thread isn't the thread which is stepping past a breakpoint.
	* gdbarch.sh (software_single_step): Update comments.
	* gdbarch.h: Regenerated.
	* infrun.c (struct step_over_info) <thread>: New field.
	(set_step_over_info): New argument 'thread'.  Callers updated.
	(clear_step_over_info): Set field thread to -1.
	(thread_is_stepping_over_breakpoint): New function.
	* infrun.h (thread_is_stepping_over_breakpoint): Declaration.

1 files changed, 6 insertions, 1 deletions

diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index 37f59b7b93..c8787c2556 100755
--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -609,7 +609,12 @@ m:CORE_ADDR:addr_bits_remove:CORE_ADDR addr:addr::core_addr_identity::0
 # target can single step.  If not, then implement single step using breakpoints.
 #
 # A return value of 1 means that the software_single_step breakpoints
-# were inserted; 0 means they were not.
+# were inserted; 0 means they were not.  Multiple breakpoints may be
+# inserted for some instructions such as conditional branch.  However,
+# each implementation must always evaluate the condition and only put
+# the breakpoint at the branch destination if the condition is true, so
+# that we ensure forward progress when stepping past a conditional
+# branch to self.
 F:int:software_single_step:struct frame_info *frame:frame
 
 # Return non-zero if the processor is executing a delay slot and a