Re: [PATCH] target/ppc: Set ctx->opcode for decode_insn32()

[Richard Henderson]

On 7/31/24 20:07, Ilya Leoshkevich wrote:
> divdu (without a dot) sometimes updates cr0, even though it shouldn't.
> The reason is that gen_op_arith_divd() checks Rc(ctx->opcode), which is
> not initialized. This field is initialized only for instructions that
> go through decode_legacy(), and not decodetree.
>
> There already was a similar issue fixed in commit 86e6202a57b1
> ("target/ppc: Make divw[u] handler method decodetree compatible.").
>
> It's not immediately clear what else may access the uninitialized
> ctx->opcode, so instead of playing whack-a-mole and changing the check
> to compute_rc0, simply initialize ctx->opcode.
>
> Cc: qemu-stable@nongnu.org
> Fixes: 99082815f17f ("target/ppc: Add infrastructure for prefixed insns")
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>

Accessing opcode from decodetree should not happen -- divd needs fixing.

But I agree this is a good short-term workaround for the release, so:
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~