Re: [PATCH v3 1/5] [PATCH 1/5] gdb/aarch64: Add POR_EL0 register support for FEAT_S1POE

[Luis <luis.machado.foss@gmail.com>]

Hi folks,

Apologies for the delayed reply.

On 07/08/2026 20:51, Srinath Parvathaneni wrote:
> Hi,
> 
>  >On 25/07/2026 07:13, Thiago Jung Bauermann wrote:
>  >> Srinath Parvathaneni <Srinath.Parvathaneni@arm.com> writes:
>  >>
>  >>>>> *  p/x $por_el0
>  >>>>> *  set $por_el0 = <value>
>  >>>>>
>  >>>>> Example:
>  >>>>> (gdb) info register por_el0
>  >>>>> por_el0 0x7 [ P15=--- P14=--- P13=--- P12=--- P11=--- P10=--- 
> P9=--- P8=--- P7=---
>  >>> P6=--- P5=--- P4=--- P3=--- P2=--- P1=--- P0=rwx ]
>  >>>>> (gdb) set $por_el0=0xffffffff77777777
>  >>>>> (gdb) info register 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) p $por_el0
>  >>>>> $1 = [ 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) p/x $por_el0
>  >>>>> $2 = 0xffffffff77777777
>  >>>>> (gdb) set $por_el0=0x57
>  >>>>> (gdb) info register por_el0
>  >>>>> por_el0 0x57 [ P15=--- P14=--- P13=--- P12=--- P11=--- P10=--- 
> P9=--- P8=--- P7=---
>  >>> P6=--- P5=--- P4=--- P3=--- P2=--- P1=rw- P0=rwx ]
>  >>>>> (gdb) set $por_el0=0xf7f7f7f7f7f7f7f7
>  >>>>> (gdb) info register por_el0
>  >>>>> por_el0 0xf7f7f7f7f7f7f7f7 [ P15=??? P14=rwx P13=??? P12=rwx 
> P11=??? P10=rwx P9=???
>  >>> P8=rwx P7=??? P6=rwx P5=??? P4=rwx P3=??? P2=rwx P1=??? P0=rwx ]
>  >>>>> (gdb)
>  >>>>
>  >>>> Looking at the output above I think it is a bit hard to read.
>  >>
>  >> I think part of the reason for it being hard to read is that the output
>  >> is very wide.
>  >
>  >Indeed. I mean, as an overview it's fine. But it really depends on the
>  >most common use case for this register.
>  >
>  >What I want to steer clear from is something like we have for SVE
>  >registers. It is a barrage of text that isn´t very easy to use.
>  >
>  >>
>  >> One way to address this is Srinath's suggestion below to not print
>  >> zeroed keys. Another would be to improve the output of the flag type to
>  >> add line breaks when the terminal's width is reached, as is done when
>  >> printing array values.
>  >>
>  >> Another option would be to use a struct rather than a flags type. Then
>  >> there would be one type per field, and it would be possible to display
>  >> (and set) only one key.
>  >>
>  >> Not sure which of them I prefer. The struct idea has the advantage of
>  >> letting the user easily set protection keys individually. OTOH it's
>  >> not printed isn a very compact way.
>  >>
>  >> If easily displaying/setting individual keys isn't that important, I
>  >> think I slightly prefer not printing zeroed keys as Srinath suggests,
>  >> possibly coupled with adding line breaks when the line is too long, to
>  >> address the case of having many keys set in the register.
>  >>
>  >
>  >Good suggestions. I'd say if users want...
>  >
>  >- An overview with permissions, then print what we have above
>  >- To use it as a mask, we should have the raw value
>  >- To read/write individual P<x> entries within the register, then we
>  >should have pseudo-registers that map back to por_el0.
>  >
>  >The pseudo registers would leave the interpretation of the raw values
>  >out of the XML, therefore remote stubs wouldn´t need to pass that sort
>  >of information.
>  >
>  >Stretching it a little bit, remote stubs could even send a modified
>  >version of these fields in the XML and gdb would start printing
>  >something else.
>  >
> 
> Hi Luis/Thiago,
> 
> After looking at the suggestions in the thread, I made a few changes to the
> POR_EL0 interface. The custom display for por_el0 has been updated, and I've
> also added support for pseudo registers for the individual permission 
> fields.
> 
> Could you please have a look at the output below? If this looks ok, I'll 
> re-spin
> the series, address the remaining review comments and send it out for 
> another
> review.
> 
> Also added a new group (por) for por_el0 register along with poe pseduo 
> registers.
> 
> Set 1:
> (gdb) info register por_el0
> por_el0        0x0000000000000077 [ P1=rwx P0=rwx ]
> (gdb) info register por
> por_el0        0x0000000000000077 [ P1=rwx P0=rwx ]
> por_el0_p0     0x7                rwx
> por_el0_p1     0x7                rwx
> por_el0_p2     0x0                ---
> por_el0_p3     0x0                ---
> por_el0_p4     0x0                ---
> por_el0_p5     0x0                ---
> por_el0_p6     0x0                ---
> por_el0_p7     0x0                ---
> por_el0_p8     0x0                ---
> por_el0_p9     0x0                ---
> por_el0_p10    0x0                ---
> por_el0_p11    0x0                ---
> por_el0_p12    0x0                ---
> por_el0_p13    0x0                ---
> por_el0_p14    0x0                ---
> por_el0_p15    0x0                ---
> 
> Set 2:
> (gdb) set $por_el0=0xf7f7f7f7f7f7f7f7
> (gdb) info register por_el0
> por_el0        0xf7f7f7f7f7f7f7f7 [ P15=??? P14=rwx P13=??? P12=rwx
>                                                             P11=??? 
> P10=rwx P9=??? P8=rwx
>                                                                   P7=??? 
> P6=rwx P5=??? P4=rwx
>                                                                   P3=??? 
> P2=rwx P1=??? P0=rwx ]
> (gdb) info register por
> por_el0        0xf7f7f7f7f7f7f7f7 [ P15=??? P14=rwx P13=??? P12=rwx
>                                                                  
>   P11=??? P10=rwx P9=??? P8=rwx
>                                                                   P7=??? 
> P6=rwx P5=??? P4=rwx
>                                                                   P3=??? 
> P2=rwx P1=??? P0=rwx ]
> por_el0_p0     0x7                       rwx
> por_el0_p1     0xf                        ???
> por_el0_p2     0x7                       rwx
> por_el0_p3     0xf                        ???
> por_el0_p4     0x7                       rwx
> por_el0_p5     0xf                      ???
> por_el0_p6     0x7                      rwx
> por_el0_p7     0xf                      ???
> por_el0_p8     0x7                            rwx
> por_el0_p9     0xf                             ???
> por_el0_p10    0x7                           rwx
> por_el0_p11    0xf                            ???
> por_el0_p12    0x7                           rwx
> por_el0_p13    0xf                            ???
> por_el0_p14    0x7                           rwx
> por_el0_p15    0xf                            ???
> 
> Set 3:
> (gdb) set $por_el0=0x0123456789abcdef
> (gdb) info register por_el0
> por_el0        0x0123456789abcdef [ P14=r-- P13=--x P12=r-x P11=-w-
>                                                   P10=rw- P9=-wx P8=rwx 
> P7=???
>                                                     P6=??? P5=??? P4=??? 
> P3=???
>                                                     P2=??? P1=??? P0=??? ]
> (gdb) info register por
> por_el0        0x0123456789abcdef [ P14=r-- P13=--x P12=r-x P11=-w-
>                                                   P10=rw- P9=-wx P8=rwx 
> P7=???
>                                                   P6=??? P5=??? P4=??? 
> P3=???
>                                                   P2=??? P1=??? P0=??? ]
> por_el0_p0     0xf                     ???
> por_el0_p1     0xe                    ???
> por_el0_p2     0xd                    ???
> por_el0_p3     0xc                    ???
> por_el0_p4     0xb                         ???
> por_el0_p5     0xa                         ???
> por_el0_p6     0x9                         ???
> por_el0_p7     0x8                         ???
> por_el0_p8     0x7                         rwx
> por_el0_p9     0x6                         -wx
> por_el0_p10    0x5                         rw-
> por_el0_p11    0x4                        -w-
> por_el0_p12    0x3                        r-x
> por_el0_p13    0x2                        --x
> por_el0_p14    0x1                        r--
> por_el0_p15    0x0                        ---
> (gdb)
> 
> Set 4:
> (gdb) set $por_el0=0x7
> (gdb) info register por
> por_el0        0x0000000000000007 [ P0=rwx ]
> por_el0_p0     0x7                        rwx
> por_el0_p1     0x0                        ---
> por_el0_p2     0x0                       ---
> por_el0_p3     0x0                        ---
> por_el0_p4     0x0                        ---
> por_el0_p5     0x0                        ---
> por_el0_p6     0x0                        ---
> por_el0_p7     0x0                        ---
> por_el0_p8     0x0                        ---
> por_el0_p9     0x0                        ---
> por_el0_p10    0x0                        ---
> por_el0_p11    0x0                        ---
> por_el0_p12    0x0                        ---
> por_el0_p13    0x0                        ---
> por_el0_p14    0x0                        ---
> por_el0_p15    0x0                        ---
> (gdb) set $por_el0_p1=0x7
> (gdb) set $por_el0_p3=0x5
> (gdb) set $por_el0_p4=0x3
> (gdb) set $por_el0_p5=0x1
> (gdb) set $por_el0_p6=0xf
> (gdb) info register por
> por_el0        0x000000000f135077 [ P6=??? P5=r-- P4=r-x P3=rw-
>                                                   P1=rwx P0=rwx ]
> por_el0_p0     0x7                     rwx
> por_el0_p1     0x7                   rwx
> por_el0_p2     0x0                         ---
> por_el0_p3     0x5                        rw-
> por_el0_p4     0x3                        r-x
> por_el0_p5     0x1                        r--
> por_el0_p6     0xf                        ???
> por_el0_p7     0x0                        ---
> por_el0_p8     0x0                        ---
> por_el0_p9     0x0                        ---
> por_el0_p10    0x0                        ---
> por_el0_p11    0x0                        ---
> por_el0_p12    0x0                        ---
> por_el0_p13    0x0                        ---
> por_el0_p14    0x0                        ---
> por_el0_p15    0x0                        ---
> (gdb)
> 
> Please let me know your comments, thanks.

Thanks. I think this improves the usability quite a bit. Two comments on 
it, both not strong opinions:

- The pseudo-register names could be shortened a bit. Or maybe 
autocompletion would work fine here.

- Do we still have value in printing por_el0's subfields given we now 
have the pseudo-registers?

As you've presented it, I think it's OK. But we might want to think 
about the above and make changes if those make sense.