Re: [Qemu-devel] [PATCH v4] target/xtensa: use libisa for instruction decoding

[Peter Maydell]

On 9 January 2018 at 18:03, Max Filippov <address@hidden> wrote:
> Replace manual opcode analysis with libisa-based code. This makes it
> possible to support variable-encoding instructions of the core ISA, like
> const16, and will allow to support advanced Xtensa features, like FLIX
> and TIE.
>
> Signed-off-by: Max Filippov <address@hidden>

Hi. Coverity (CID 1385146) complains about this bit of code:

> +        opnds = xtensa_opcode_num_operands(isa, opc);
> +
> +        for (opnd = vopnd = 0; opnd < opnds; ++opnd) {
> +            if (xtensa_operand_is_visible(isa, opc, opnd)) {
> +                uint32_t v;

because xtensa_opcode_num_operands() can return -1
(if the CHECK_OPCODE() fails), and then we will try to use
-1 as an upper bound for this loop and it will loop for a very
long time.

CID 1385148 is similar but for the outer loop where
we do "slots = xtensa_format_num_slots()" and then use
slots as a loop bound without checking whether we got back -1.

thanks
-- PMM