Re: [PATCH v4 1/5] gdb/aarch64: Add POR_EL0 register support for FEAT_S1POE

[Thiago Jung Bauermann <thiago.bauermann@linaro.org>]

Thiago Jung Bauermann <thiago.bauermann@linaro.org> writes:

> <srinath.parvathaneni@arm.com> writes:
>
>> Add support for the FEAT_S1POE POR_EL0 register on AArch64.
>>
>> This patch adds POR_EL0 to the AArch64 register set and reads/writes it
>> using the NT_ARM_POE ptrace regset.
>>
>> It also adds POE pseudo-registers por_p0 through por_p15, with each
>> pseudo-register mapping to a 4-bit field in POR_EL0, starting from the
>> least-significant nibble.
>>
>> POR_EL0 and the POE pseudo-registers are added to the "por" register
>> group, allowing them to be displayed together using the
>> "info registers por" command.
>>
>> With this change, POR_EL0 is accessible through:
>>
>> * info registers
>> * info registers por_el0
>> * info registers por
>> * p $por_el0
>> * p/x $por_el0
>> * set $por_el0 = <value>
>>
>> The individual POE fields can also be accessed and modified through
>> $por_p0 to $por_p15.
>>
>> Example:
>> (gdb) info register por_el0
>> por_el0        0x7                 [ P0=rwx ]
>> (gdb) set $por_el0=0xffffffff77777777
>> (gdb) info registers por_el0
>> por_el0        0xffffffff77777777 [ P15=??? P14=??? P13=??? P12=???
>>                                     P11=??? P10=??? P9=??? P8=???
>>                                     P7=rwx P6=rwx P5=rwx P4=rwx
>>                                     P3=rwx P2=rwx P1=rwx P0=rwx ]
>> (gdb) info registers por
>> por_el0        0xffffffff77777777 [ P15=??? P14=??? P13=??? P12=???
>>                                     P11=??? P10=??? P9=??? P8=???
>>                                     P7=rwx P6=rwx P5=rwx P4=rwx
>>                                     P3=rwx P2=rwx P1=rwx P0=rwx ]
>> por_p0         0x7                rwx
>> por_p1         0x7                rwx
>> por_p2         0x7                rwx
>> por_p3         0x7                rwx
>> por_p4         0x7                rwx
>> por_p5         0x7                rwx
>> por_p6         0x7                rwx
>> por_p7         0x7                rwx
>> por_p8         0xf                ???
>> por_p9         0xf                ???
>> por_p10        0xf                ???
>> por_p11        0xf                ???
>> por_p12        0xf                ???
>> por_p13        0xf                ???
>> por_p14        0xf                ???
>> por_p15        0xf                ???
>>
>> Individual POE pseudo-registers can be written independently, with the
>> corresponding 4-bit field in POR_EL0 updated accordingly.  For example:
>>
>> (gdb) set $por_el0=0x7
>> (gdb) info registers por_el0
>> por_el0        0x0000000000000007 [ P0=rwx ]
>> (gdb) set $por_p1=0x7
>> (gdb) info registers por_el0
>> por_el0        0x0000000000000077 [ P1=rwx P0=rwx ]
>
> I like this output and the pseudo registers. Thanks!

One more thing that I remembered today:

Considering that the print command doesn't show the "pretty" output:

(gdb) p $por_el0
$1 = 21474836487
(gdb) p/x $por_el0
$2 = 0x500000007
(gdb) p $por_p8
$3 = 5

It would be useful to add a new "Permission Overlay Extension" section
in the GDB manual (under Configurations → Architectures → AArch64)
mentioning the use of the "info registers" command to get the fancier
output, the poe register group and setting/getting individual fields
with the pseudo-registers.

-- 
Thiago
(he/him)