Re: [PATCH for-7.1 v6 39/51] target/nios2: Implement Misaligned destination exception

[Richard Henderson]

On 3/17/22 09:37, Peter Maydell wrote:
> The spec isn't clear about whether an unaligned-destination on
> an eret is handled as "do the eret (ie restore status), then take
> the exception when trying to set the new PC" or "take the exception
> immediately" (ie whether it's always a nested exception, effectively).
> I guess this is as good a guess as any.

The way I read the spec the first time is that the pc as reported to the exception points 
to the eret, and it's only badaddr that contains the misaligned address.  I simply assumed 
that would mean that the status change hadn't happened either.

I also see that I've failed to update gen_bxx for this.  Also unspecified is if the trap 
for e.g. beq happens *whenever* the low two bits of imm16 are set, or only if the equality 
holds.  I'm tempted to do the former -- other architectures would treat that case as an 
illegal instruction.


r~