Re: [Qemu-devel] running out of Arm TB flags...

[Alex Bennée]

Richard Henderson <address@hidden> writes:

> On 3/18/19 12:46 PM, Peter Maydell wrote:
>> Hi; for the M-profile floating point work I'm going to need I think
>> three new TB flags (to control whether to generate the code to do
>> the various independent things the pseudocode ExecuteFPCheck() function
>> does before executing any FP insn). Unfortunately we currently have
>> only 2 unused bits in the arm TB flags word.
>>
>> I can see two possible ways to get the 3rd bit:
>> (1) overload the meaning of an existing bit which I know isn't
>> relevant to M-profile (eg the XSCALE_CPAR or VECLEN or VECSTRIDE bits)
>> (2) start defining new bits in the currently-unused cs_base word
>
> Either works.  But I'd probably reuse (or eliminate) XSCALE_CPAR first.
> Afaik, xscale never had vfp, so CPAR could overlap FPEXC_EL?

Agree, we should certainly be efficient with the base flags first (we
already have overlap for AA32/64 states). I have no problem with using
cs_base after that. We could bite the bullet and expand flags to 64 bits
but I guess that will be a bit of a hit for 32 bit hosts.

Given how many guests use the cs_base I wonder if it's time we came up
with a better name for it: extra_tb_state, extra_state, moar_bits...

>
>
> r~


--
Alex Bennée