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

[Torbjorn SVENSSON <torbjorn.svensson@foss.st.com>]

On 2022-11-08 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".
> 
> 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!

This was fixed in 5.9.0 and the latest released version i 7.0.0.

IIRC, SEGGER JLink exposes both CONTROL registers too, but I can't 
confirm that right now.

Kind regards,
Torbjörn