From: Yao Qi <qiyaoltc@gmail.com>
To: Pedro Alves <palves@redhat.com>
Cc: Yao Qi <qiyaoltc@gmail.com>, gdb-patches@sourceware.org
Subject: Re: [PATCH 3/7] Force to insert software single step breakpoint
Date: Wed, 20 Apr 2016 07:50:00 -0000 [thread overview]
Message-ID: <861t60k9dl.fsf@gmail.com> (raw)
In-Reply-To: <570BB52F.7@redhat.com> (Pedro Alves's message of "Mon, 11 Apr 2016 15:31:11 +0100")
Pedro Alves <palves@redhat.com> writes:
> Sounds like we may need to look at the single-step breakpoint's thread
> id, and only insert it if it is for the thread that is going to be
> doing the step-over? We may need to record that in step_over_info and
> pass more info to stepping_past_instruction_at.
The patch below does this, however, I don't pass more info to
stepping_past_instruction_at, instead I add a new function
thread_is_being_stepped_over_p.
>
>> --- a/gdb/gdbarch.sh
>> +++ b/gdb/gdbarch.sh
>> @@ -609,7 +609,10 @@ 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.
>
> I'd add:
>
> (...) condition is true, so that we ensure forward progress when
> stepping past a conditional branch to self.
>
> This will help porters evaluate whether that's really necessary
> for their ports.
Done.
--
Yao (齐尧)
Subject: [PATCH] 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:
2016-04-20 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 brekapoint's
owner isn't the thread we are stepping over.
* 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_being_stepped_over_p): New function.
* infrun.h (thread_is_being_stepped_over_p): Declaration.
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index f99a7ab..64e97c6 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -2219,11 +2219,22 @@ should_be_inserted (struct bp_location *bl)
return 0;
/* Don't insert a breakpoint if we're trying to step past its
- location. */
+ location except that the breakpoint is single-step breakpoint
+ and the single-step breakpoint's owner is the thread we're
+ stepping over. */
if ((bl->loc_type == bp_loc_software_breakpoint
|| bl->loc_type == bp_loc_hardware_breakpoint)
&& stepping_past_instruction_at (bl->pspace->aspace,
- bl->address))
+ bl->address)
+ /* The single-step breakpoint may be inserted at the location
+ we're trying to step if the instruction branches to itself.
+ However, the instruction won't be executed at all and it may
+ break the semantics of the instruction, for example, the
+ instruction is a conditional branch or updates some flags.
+ We can't fix it unless GDB is able to emulate the instruction
+ or switch to displaced stepping. */
+ && !(bl->owner->type == bp_single_step
+ && thread_is_being_stepped_over_p (bl->owner->thread)))
{
if (debug_infrun)
{
diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 252fc4b..859ba85 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -650,7 +650,12 @@ extern void set_gdbarch_addr_bits_remove (struct gdbarch *gdbarch, gdbarch_addr_
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. */
extern int gdbarch_software_single_step_p (struct gdbarch *gdbarch);
diff --git a/gdb/gdbarch.sh b/gdb/gdbarch.sh
index 37f59b7..c8787c2 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
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 696105d..1ccd648 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1296,6 +1296,9 @@ struct step_over_info
/* The instruction being stepped over triggers a nonsteppable
watchpoint. If true, we'll skip inserting watchpoints. */
int nonsteppable_watchpoint_p;
+
+ /* The thread's global number. */
+ int thread;
};
/* The step-over info of the location that is being stepped over.
@@ -1329,11 +1332,13 @@ static struct step_over_info step_over_info;
static void
set_step_over_info (struct address_space *aspace, CORE_ADDR address,
- int nonsteppable_watchpoint_p)
+ int nonsteppable_watchpoint_p,
+ int thread)
{
step_over_info.aspace = aspace;
step_over_info.address = address;
step_over_info.nonsteppable_watchpoint_p = nonsteppable_watchpoint_p;
+ step_over_info.thread = thread;
}
/* Called when we're not longer stepping over a breakpoint / an
@@ -1348,6 +1353,7 @@ clear_step_over_info (void)
step_over_info.aspace = NULL;
step_over_info.address = 0;
step_over_info.nonsteppable_watchpoint_p = 0;
+ step_over_info.thread = -1;
}
/* See infrun.h. */
@@ -1365,6 +1371,15 @@ stepping_past_instruction_at (struct address_space *aspace,
/* See infrun.h. */
int
+thread_is_being_stepped_over_p (int thread)
+{
+ return (step_over_info.aspace != NULL
+ && thread == step_over_info.thread);
+}
+
+/* See infrun.h. */
+
+int
stepping_past_nonsteppable_watchpoint (void)
{
return step_over_info.nonsteppable_watchpoint_p;
@@ -2579,7 +2594,7 @@ resume (enum gdb_signal sig)
stop_all_threads ();
set_step_over_info (get_regcache_aspace (regcache),
- regcache_read_pc (regcache), 0);
+ regcache_read_pc (regcache), 0, tp->global_num);
step = maybe_software_singlestep (gdbarch, pc);
@@ -7750,10 +7765,11 @@ keep_going_pass_signal (struct execution_control_state *ecs)
&& (remove_wps || !use_displaced_stepping (ecs->event_thread)))
{
set_step_over_info (get_regcache_aspace (regcache),
- regcache_read_pc (regcache), remove_wps);
+ regcache_read_pc (regcache), remove_wps,
+ ecs->event_thread->global_num);
}
else if (remove_wps)
- set_step_over_info (NULL, 0, remove_wps);
+ set_step_over_info (NULL, 0, remove_wps, -1);
/* If we now need to do an in-line step-over, we need to stop
all other threads. Note this must be done before
diff --git a/gdb/infrun.h b/gdb/infrun.h
index 61d3b20..5f98414 100644
--- a/gdb/infrun.h
+++ b/gdb/infrun.h
@@ -133,6 +133,10 @@ extern void insert_step_resume_breakpoint_at_sal (struct gdbarch *,
extern int stepping_past_instruction_at (struct address_space *aspace,
CORE_ADDR address);
+/* Returns true if thread whose thread number is THREAD is being
+ stepped over. */
+extern int thread_is_being_stepped_over_p (int thread);
+
/* Returns true if we're trying to step past an instruction that
triggers a non-steppable watchpoint. */
extern int stepping_past_nonsteppable_watchpoint (void);
next prev parent reply other threads:[~2016-04-20 7:50 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-23 16:10 [PATCH 0/7 V2] Step over instruction branches to itself Yao Qi
2016-03-23 16:10 ` [PATCH 5/7] [GDBserver] Don't error in reinsert_raw_breakpoint if bp->inserted Yao Qi
2016-04-11 14:54 ` Pedro Alves
2016-03-23 16:10 ` [PATCH 1/7] New test case gdb.trace/signal.exp Yao Qi
2016-04-08 16:52 ` Pedro Alves
2016-04-11 8:41 ` Yao Qi
2016-04-11 14:04 ` Pedro Alves
2016-04-22 10:53 ` Yao Qi
2016-04-26 12:57 ` Pedro Alves
2016-04-11 14:08 ` Pedro Alves
2016-03-23 16:10 ` [PATCH 3/7] Force to insert software single step breakpoint Yao Qi
2016-04-11 14:31 ` Pedro Alves
2016-04-13 16:21 ` Yao Qi
2016-04-19 14:54 ` Yao Qi
2016-04-19 15:17 ` Pedro Alves
2016-04-20 7:50 ` Yao Qi [this message]
2016-04-22 16:36 ` Pedro Alves
2016-04-25 8:40 ` Yao Qi
2016-03-23 16:10 ` [PATCH 6/7] Resume the inferior with signal rather than stepping over Yao Qi
2016-04-11 15:29 ` Pedro Alves
2016-03-23 16:10 ` [PATCH 4/7] Insert breakpoint even when the raw breakpoint is found Yao Qi
2016-04-11 14:41 ` Pedro Alves
2016-04-12 9:04 ` Yao Qi
2016-04-12 9:41 ` Pedro Alves
2016-04-25 8:45 ` Yao Qi
2016-03-23 16:10 ` [PATCH 2/7] Deliver signal in hardware single step Yao Qi
2016-04-11 14:10 ` Pedro Alves
2016-04-22 10:54 ` Yao Qi
2016-03-23 16:26 ` [PATCH 7/7] New test case gdb.base/branch-to-self.exp Yao Qi
2016-04-11 15:34 ` Pedro Alves
2016-04-25 8:58 ` Yao Qi
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