Re: [PATCH 1/1] disas/riscv: Guard dec->cfg dereference for host disassemble

[Richard Henderson <richard.henderson@linaro.org>]

On 12/5/24 22:39, LIU Zhiwei wrote:
> 
> Both zcmt and zcmp are not compatible with Zcd, as they reuse some encodings from c.fsdsp.

Ok, fair.  A comment about conflicts at that point may help.

> 
> Zimop or Zcmop also overlap with other isa extensions, as they are maybe-ops. Other extensions
> such as zicfiss will reuse their encodings.
> 
> I think we had better disassemble them to zicifss if it has been implemented on the target cpu. Otherwise
> we disassemble them to maybe-ops.

My point is that they are only belong to zimop until they are assigned, like zicifss.
At that point they *have* a defined meaning in the standard isa.

So, yes, disassemble as zicifss, but always, not "if it has been implemented in the target 
cpu".

>>> +        if (((i == 0) || cfg) && guard_func(cfg)) {
>>
>> This should be i == 0 || (cfg && guard_func(cfg)).
> 
> OK. Although I think they are both right.

  i = 0
  cfg = NULL

    (0 == 0 || NULL) && guard_func(NULL)
-> (true || false) && guard_func(NULL)
-> true && guard_func(NULL)
-> guard_func(NULL)
-> boom.

Or are you saying it won't go boom because we happen to know the 0th guard_func only 
returns true?  There's still no reason to call it...


r~