Re: [Qemu-devel] Support for ARM CP15 registers via GDB interface of qemu

[Abhijit Ray Chaudhury]

Hi Peter,

Thanks for your prompt response. I have gone through target
description xml format for gdb
(https://sourceware.org/gdb//onlinedocs/gdb/ARM-Features.html#ARM-Features)
. I could not find a feature description matching cp15 registers.So
even if I implement some subset of it would gdb understand it ? Can I
randomly name SCTLR TTBR0 etc and gdb understand it ?

Thanking You,
-Abhijit

On Fri, Sep 22, 2017 at 4:23 PM, Peter Maydell <address@hidden> wrote:
> On 22 September 2017 at 11:39, Abhijit Ray Chaudhury
> <address@hidden> wrote:
>> I want to view ARM CP15 register sets via gdb when I am emulating arm.
>> However I only see ARM Core Register Sets and NEON registers through
>> gdb interface.
>>
>> Can you please let me know how to add cp15 register set support using
>> gdb interface in qemu.
>
> This isn't currently implemented in QEMU, though it would be a
> nice idea. We have wishlist bug https://bugs.launchpad.net/qemu/+bug/741115
> about this, though that was filed in 2011 which will give you an
> idea of how likely it is to be implemented.
>
> The implementation would be moderately but not insanely complex:
> we would need to generate XML in the gdbstub that describes the
> registers by enumerating them in the cpreg hashtable. Hopefully
> gdb would then be able to handle the registers we describe to
> it that way. Likely pitfalls along the way:
>  * our gdbstub currently breaks if the XML fragment is too large,
>    so that bug would need to be fixed first
>  * The coprocessor register descriptions currently assume things
>    like the register name string are for debug purposes only,
>    so there are probably duplicate names or otherwise unhelpful
>    things in there -- these would need to be located and fixed
>
> I thought I remembered somebody talking about having a go at
> implementing this, but I can't find anything with a search through
> the qemu-devel mail archive, so I guess I'm mistaken.
>
> thanks
> -- PMM