[Qemu-devel] [PATCH] target-arm: Fix arm_debug_excp_handler() for singlestep enabled

[Qemu-devel] [PATCH] target-arm: Fix arm_debug_excp_handler() for singlestep enabled

[Sergey Fedorov]

CPU singlestep is done by generating a debug internal exception. Do not
raise a real CPU exception in case of singlestepping.

Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
---
 target-arm/op_helper.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 7929c71..67d9ffb 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -909,7 +909,7 @@ void arm_debug_excp_handler(CPUState *cs)
         uint64_t pc = is_a64(env) ? env->pc : env->regs[15];
         bool same_el = (arm_debug_target_el(env) == arm_current_el(env));
 
-        if (cpu_breakpoint_test(cs, pc, BP_GDB)) {
+        if (cs->singlestep_enabled || cpu_breakpoint_test(cs, pc, BP_GDB)) {
             return;
         }
 
-- 
1.9.1

Re: [Qemu-devel] [PATCH] target-arm: Fix arm_debug_excp_handler() for singlestep enabled

[Peter Maydell]

On 2 November 2015 at 17:51, Sergey Fedorov <serge.fdrv@gmail.com> wrote:
> CPU singlestep is done by generating a debug internal exception. Do not
> raise a real CPU exception in case of singlestepping.
>
> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
> ---
>  target-arm/op_helper.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
> index 7929c71..67d9ffb 100644
> --- a/target-arm/op_helper.c
> +++ b/target-arm/op_helper.c
> @@ -909,7 +909,7 @@ void arm_debug_excp_handler(CPUState *cs)
>          uint64_t pc = is_a64(env) ? env->pc : env->regs[15];
>          bool same_el = (arm_debug_target_el(env) == arm_current_el(env));
>
> -        if (cpu_breakpoint_test(cs, pc, BP_GDB)) {
> +        if (cs->singlestep_enabled || cpu_breakpoint_test(cs, pc, BP_GDB)) {
>              return;
>          }

So I think this will mean that if we're gdbstub-single-stepping then
an architectural breakpoint on the insn we're stepping won't fire.

Does using a test

if (!cpu_breakpoint_test(cs, pc, BP_CPU)) {
    return;
}

fix the singlestep bug too? If so I think it would probably be
preferable.

thanks
-- PMM

Re: [Qemu-devel] [PATCH] target-arm: Fix arm_debug_excp_handler() for singlestep enabled

[Sergey Fedorov]

On 02.11.2015 21:28, Peter Maydell wrote:
> On 2 November 2015 at 17:51, Sergey Fedorov <serge.fdrv@gmail.com> wrote:
>> CPU singlestep is done by generating a debug internal exception. Do not
>> raise a real CPU exception in case of singlestepping.
>>
>> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
>> ---
>>  target-arm/op_helper.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
>> index 7929c71..67d9ffb 100644
>> --- a/target-arm/op_helper.c
>> +++ b/target-arm/op_helper.c
>> @@ -909,7 +909,7 @@ void arm_debug_excp_handler(CPUState *cs)
>>          uint64_t pc = is_a64(env) ? env->pc : env->regs[15];
>>          bool same_el = (arm_debug_target_el(env) == arm_current_el(env));
>>
>> -        if (cpu_breakpoint_test(cs, pc, BP_GDB)) {
>> +        if (cs->singlestep_enabled || cpu_breakpoint_test(cs, pc, BP_GDB)) {
>>              return;
>>          }
> So I think this will mean that if we're gdbstub-single-stepping then
> an architectural breakpoint on the insn we're stepping won't fire.
>
> Does using a test
>
> if (!cpu_breakpoint_test(cs, pc, BP_CPU)) {
>     return;
> }
>
> fix the singlestep bug too? If so I think it would probably be
> preferable.

Actually, it is supposed that gdbstub breakpoints should be handled
before CPU breakpoints. So I think we should rather do this way:

if (cpu_breakpoint_test(cs, pc, BP_GDB) || !cpu_breakpoint_test(cs, pc, BP_CPU)) {
    return;
}


Thanks,
Sergey

Re: [Qemu-devel] [PATCH] target-arm: Fix arm_debug_excp_handler() for singlestep enabled

[Peter Maydell]

On 3 November 2015 at 09:02, Sergey Fedorov <serge.fdrv@gmail.com> wrote:
> On 02.11.2015 21:28, Peter Maydell wrote:
>> On 2 November 2015 at 17:51, Sergey Fedorov <serge.fdrv@gmail.com> wrote:
>>> CPU singlestep is done by generating a debug internal exception. Do not
>>> raise a real CPU exception in case of singlestepping.
>>>
>>> Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com>
>>> ---
>>>  target-arm/op_helper.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
>>> index 7929c71..67d9ffb 100644
>>> --- a/target-arm/op_helper.c
>>> +++ b/target-arm/op_helper.c
>>> @@ -909,7 +909,7 @@ void arm_debug_excp_handler(CPUState *cs)
>>>          uint64_t pc = is_a64(env) ? env->pc : env->regs[15];
>>>          bool same_el = (arm_debug_target_el(env) == arm_current_el(env));
>>>
>>> -        if (cpu_breakpoint_test(cs, pc, BP_GDB)) {
>>> +        if (cs->singlestep_enabled || cpu_breakpoint_test(cs, pc, BP_GDB)) {
>>>              return;
>>>          }
>> So I think this will mean that if we're gdbstub-single-stepping then
>> an architectural breakpoint on the insn we're stepping won't fire.
>>
>> Does using a test
>>
>> if (!cpu_breakpoint_test(cs, pc, BP_CPU)) {
>>     return;
>> }
>>
>> fix the singlestep bug too? If so I think it would probably be
>> preferable.
>
> Actually, it is supposed that gdbstub breakpoints should be handled
> before CPU breakpoints. So I think we should rather do this way:
>
> if (cpu_breakpoint_test(cs, pc, BP_GDB) || !cpu_breakpoint_test(cs, pc, BP_CPU)) {
>     return;
> }

Yes, that sounds like the right logic. I think a comment will be
helpful to explain what's going on for future readers :-)

thanks
-- PMM