Re: [Qemu-devel] [PATCH 2/2] milkymist-pfpu: fix GCC 5.0.0 aggressive-loop-optimizations warning

[Paolo Bonzini]

On 20/02/2015 15:52, Michael Walle wrote:
>>>
>>> -            i = 0;
>>> -            while (pfpu_decode_insn(s)) {
>>> -                /* decode at most MICROCODE_WORDS instructions */
>>> -                if (i++ >= MICROCODE_WORDS) {
>>
>> Isn't the fix just to say "++i" instead of "i++"?
> 
> In the first run, s->regs[R_PC] may have any value, therefore the "insn
> = s->microcode[pc]" from above may access out of bounds.

Then should pfpu_decode_insn access s->microcode[pc & (MICROCODE_WORDS -
1)]?  That's likely what happens in hardware, and the purpose of the
error is just to avoid an infinite loop in device code.

Paolo