Re: [RFC PATCH] target/s390x: don't double ld_code() when reading instructions

[Alex Bennée]

Richard Henderson <richard.henderson@linaro.org> writes:

> On 10/12/21 2:31 AM, Alex Bennée wrote:
>> For the 4 byte instruction case we started doing an ld_code2 and then
>> reloaded the data with ld_code4 once it was identified as a 4 byte op.
>> This is confusing for the plugin hooks which are expecting to see
>> simple sequential loading so end up reporting a malformed 6 byte
>> instruction buffer.
>
> I think the plugin stuff could be more clever, knowing where the read
> occurs within the sequence.  Otherwise, we should simplify the
> interface so that it is not possible to make this mistake.

It's plugin_insn_append which is doing the tracking here so we could
extend the interface to include the current pc of the load and make the
appropriate adjustments. That said it's a bunch hoops to jump every
instruction when we could just as easily add an assert and fix up any
cases where we do. I guess it comes down to how prevalent double dipping
in the instruction stream is when constructing a translation?

What happens if the protection of the code area changes half way through
a translation? Could a mapping change in flight?

>
>
> r~


-- 
Alex Bennée