Re: [RISU v2 14/17] Add magic and size to the trace header

[Richard Henderson]

On 5/18/20 7:53 PM, Richard Henderson wrote:
> +    if (master_header.magic != RISU_MAGIC ||
> +        master_header.risu_op != op ||
> +        master_header.size != extra_size) {
> +        res = RES_MISMATCH_HEAD;
> +        goto fail_header;
>      }

Hmm.  This isn't ideal.

Consider e.g. an insn being tested that should pass, so master steps past the
insn to the UDF and sends OP_COMPARE.  But there's a bug in the emulator being
tested so the apprentice gets SIGILL on the insn and so op == OP_SIGILL.

So risu_op != op, but we only report the header difference.

Perhaps that's good enough to understand the this particular problem, without
the clutter of printing the rest of the reginfo frame -- at least if
report_mismatch_header is improved to print risu_op names instead of numbers.

Consider if master and apprentice are run with different --test-sve=<vq>
values.  That will produce a mismatch in size.

Which could be a serious problem, if master_header.size > sizeof(master_ri) --
we can't even receive the data.  In that case, what I'm doing here printing the
size mismatch is all that's possible.

But suppose master_header.size <= sizeof(master_ri), so we can receive the
data.  So long as master_header.size == reginfo_size(&master_ri), then at least
the data is self-consistent, and we *can* print out the difference in
report_mismatch_reg().  Which in this case is going to be the difference in the
two ri->sve_vl values.  That difference is likely to be easiest to understand
for the end user.

I should probably split out this receive logic from
recv_and_compare_register_info so that it can be reused by dump.


r~