Re: [PATCH v3] Enable tracing of pseudo-registers on ARM

Pedro Alves
2016-02-24T18:33:58Z

On 02/24/2016 06:20 PM, Marcin KoÅ›cielnicki wrote:
> On 24/02/16 19:11, Pedro Alves wrote:
>> On 02/22/2016 04:51 PM, Antoine Tremblay wrote:
>>>

>>> While looking at fixing this for all the archs involved it would be
>>> much simpler to test if gdbserver would make use of it.
>>>
>>> As it is now, I'm concerned that calling gdbarch_remote_register_number
>>> in ax_reg, ax_mask_reg could break things if the arch already considers
>>> the gdb raw -> target raw mapping like s390 and x86 do already (I'm not
>>> 100% sure the mapping is already ok)?
>>
>> WDTM? Where do they do this already?
>
> FWIW, I failed to look at the numbering used when I wrote the x86 and
> s390 ax functions, so they're most likely wrong (I just copied the
> regnum computation logic from pseudo_read/write, which uses gdb
> numbers). s390 hasn't landed yet, so it's only x86 that you'd have to
> fix now (and mips, I think, but that doesn't support tracepoints yet...).

I don't think there's anything that needs fixing in the i386 implementation.

The x86 implementation maps gdb pseudo register numbers to whatever
raw gdb registers back the former up, like:

ax_reg_mask (ax, I387_FSTAT_REGNUM (tdep));

That OK.

The trouble is that in the end we send gdb numbers to the target in the
ax, instead of tdesc/remote numbers.

We never noticed because gdbserver always collects all raw registers
anyway.

Seems to me that the fix is to make ax_reg / ax_reg_mask take gdb raw
numbers as input (as it does today), and then make it map those to
tdesc/remote number just before it puts the reg number in the agent
expression bytecode / reg mask. And that covers all archs.

>
> Testing this is possible if you write some conditions that involve
> reading pseudo-registers (since ax_pseudo_register_push_stack will be
> called), the problem is that I only implemented
> ax_pseudo_register_collect for x86...
>
> Are you going to make some higher-level patch that will magically fix it
> for my s390 patch, or do I have to fix that on my own?

I haven't memorized your s390 patch :-) but there's probably nothing to
do on the s390-specific bits.

Thanks,
Pedro Alves