Re: [RFC PATCH 1/5] gdb/arm: Introduce control_s and control_ns registers

[Luis Machado <luis.machado@arm.com>]

Hi,

On 11/8/22 15:58, Tomas Vanek wrote:
> On 08/11/2022 16:52, Tomas Vanek wrote:
>> Hi Luis,
>>
>> On 08/11/2022 12:23, Luis Machado wrote:
>>> Hi Tomas,
>>>
>>> On 11/5/22 09:44, Tomas Vanek wrote:
>>>> The M-profile security extension registers will be used for stack
>>>> selection in FNC_RETURN and return from secure to non-secure state.
>>>>
>>>> The presence of the registers is optional.
>>>> If one or both are missing the security extension profile is accepted.
>>>> The code using the registers must check m_profile_control_[n]?s_regnum
>>>> for -1.
>>>>
>>>> Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
>>>> ---
>>>>   gdb/arm-tdep.c | 20 ++++++++++++++++++++
>>>>   gdb/arm-tdep.h |  2 ++
>>>>   2 files changed, 22 insertions(+)
>>>>
>>>> diff --git a/gdb/arm-tdep.c b/gdb/arm-tdep.c
>>>> index 3105543..564ee43 100644
>>>> --- a/gdb/arm-tdep.c
>>>> +++ b/gdb/arm-tdep.c
>>>> @@ -9996,6 +9996,8 @@ enum arm_vfp_cprc_base_type
>>>>     int m_profile_psp_ns_regnum = -1;
>>>>     int m_profile_msp_s_regnum = -1;
>>>>     int m_profile_psp_s_regnum = -1;
>>>> +  int m_profile_control_s_regnum = -1;
>>>> +  int m_profile_control_ns_regnum = -1;
>>>>     int tls_regnum = 0;
>>>>       /* If we have an object to base this architecture on, try to determine
>>>> @@ -10473,6 +10475,22 @@ enum arm_vfp_cprc_base_type
>>>>           }
>>>>             m_profile_psp_s_regnum = register_count++;
>>>>   +          /* Regard the control_s and control_ns registers optional,
>>>> +           * accept the security extension feature even without them */
>>>> +          valid_p = tdesc_numbered_register (feature, tdesc_data.get (),
>>>> +                         register_count, "control_s");
>>>
>>> What tools are advertising control_s and control_ns? We need to document those properly if we're planning on using them
>>> as part of decision-making in GDB.
>>
>> Good question.
>>
>> OpenOCD exposes them, like other M-profile security extension registers they have the feature name "v8-m.sp".
>> There is a pending patch to change the feature name to "org.gnu.gdb.arm.secext"
>> 7265: target/armv7m: fix feature name of ARMv8M security extension regs | https://review.openocd.org/c/openocd/+/7265
>>
>> PyOCD exposes them, like other M-profile security extension registers they have the feature name "v8-m.sp".
> 
> Oops, PyOCD exposes just control, no control_s and control_ns variants.
> 

Should we coordinate this a bit better between PyOCD and ST-LINK to expose the same set of registers. That would make it easier for
gdb to deal with it.

>>
>> ST-LINK GDB server. Version 5.6.0 (I assume not the latest version) exposes them (and other M-profile security extension registers too)
>> in the feature "org.gnu.gdb.arm.vfp"?? Obviously a bug!
>>
>> I have no access to Keil tools.
>>
>> Please be aware that control_s and control_ns are optional, the most of security extension support is functional
>> even in the case they are not accessible in the connected gdbserver.
>>
>>>
>>>
>>>> +          if (!valid_p)
>>>> +        warning (_("M-profile secext feature is missing required register control_s."));
>>>> +          else
>>>> +        m_profile_control_s_regnum = register_count++;
>>>> +
>>>> +          valid_p = tdesc_numbered_register (feature, tdesc_data.get (),
>>>> +                         register_count, "control_ns");
>>>> +          if (!valid_p)
>>>> +        warning (_("M-profile secext feature is missing required register control_ns."));
>>>> +          else
>>>> +        m_profile_control_ns_regnum = register_count++;
>>>> +
>>>>             have_sec_ext = true;
>>>>           }
>>>>   @@ -10553,6 +10571,8 @@ enum arm_vfp_cprc_base_type
>>>>         tdep->m_profile_psp_ns_regnum = m_profile_psp_ns_regnum;
>>>>         tdep->m_profile_msp_s_regnum = m_profile_msp_s_regnum;
>>>>         tdep->m_profile_psp_s_regnum = m_profile_psp_s_regnum;
>>>> +      tdep->m_profile_control_s_regnum = m_profile_control_s_regnum;
>>>> +      tdep->m_profile_control_ns_regnum = m_profile_control_ns_regnum;
>>>>       }
>>>>       arm_register_g_packet_guesses (gdbarch);
>>>> diff --git a/gdb/arm-tdep.h b/gdb/arm-tdep.h
>>>> index bcd7e08..11670e9 100644
>>>> --- a/gdb/arm-tdep.h
>>>> +++ b/gdb/arm-tdep.h
>>>> @@ -133,6 +133,8 @@ struct arm_gdbarch_tdep : gdbarch_tdep_base
>>>>     int m_profile_psp_ns_regnum = ARM_SP_REGNUM;    /* M-profile PSP_NS register number.  */
>>>>     int m_profile_msp_s_regnum = ARM_SP_REGNUM;    /* M-profile MSP_S register number.  */
>>>>     int m_profile_psp_s_regnum = ARM_SP_REGNUM;    /* M-profile PSP_S register number.  */
>>>> +  int m_profile_control_s_regnum = -1;        /* M-profile CONTROL_S register number.  */
>>>> +  int m_profile_control_ns_regnum = -1;        /* M-profile CONTROL_NS register number.  */
>>>>       int tls_regnum = 0;        /* Number of the tpidruro register.  */
>>>
>>
>