Re: [PATCH 2/2] target/arm: Look up ARMCPRegInfo at runtime

[Richard Henderson]

On 1/23/23 02:53, Peter Maydell wrote:
> On Fri, 6 Jan 2023 at 19:45, Richard Henderson
> <richard.henderson@linaro.org> wrote:
> > Do not encode the pointer as a constant in the opcode stream.
> > This pointer is specific to the cpu that first generated the
> > translation, which runs into problems with both hot-pluggable
> > cpus and user-only threads, as cpus are removed.
> >
> > Perform the lookup in either helper_access_check_cp_reg,
> > or a new helper_lookup_cp_reg.
>
> As well as the use-after-free, this is also a correctness
> bug, isn't it? If we hardwire in the cpregs pointer for
> CPU 0 into the TB, and then CPU 1 with a slightly different
> config executes the TB, it will get the cpregs of CPU 0,
> not its own, so it might see a register it should not or
> vice-versa.

Existing assumption was that each cpu configuration would have its own cluster_index, 
which gets encoded into cpu->tcg_cflags, which is part of the comparison used when hashing 
TBs.

But including this patch allows relaxation of what constitutes a "cpu 
configuration".


r~