[PATCH v4] Fixups of Loongson2F

[Sam Kuper]

On 19/11/2009, Wu Zhangjin <wuzhangjin@gmail.com> wrote:

I have three questions.

> The NOP issue has been solved in latest loongson2f batches, but this fix has no
> side effect to them since the "or at,at,zero" is also a dummy instruction.

Question 1: On a Yeeloong running GNU/Linux, is there a command the
user can enter in order to discover whether the Loongson2F in that
Yeeloong came from a batch with the NOP issue fix?

> -mfix-loongson2f-jump inserts three instructions before the J,JR,JALR
> instructions to eliminate instruction fetch from outside 256M region to work
> around the JUMP instructions issue(only with some specific external chips, such
> as CS5536.). Without it, under extreme cases, kernel may hang/crash with
> unpredictable memory access. This fix may bring us with some potential
> overhead. This issue has been solved in latest loongson2f batches.

Question 2: On a Yeeloong running GNU/Linux, is there a command the
user can enter in order to discover whether the Loongson2F in that
Yeeloong came from a batch with the JUMP issue fix?

Question 3: If the Loongson2F in a Yeeloong came from an unfixed
batch, could a malicious non-root user who was legitimately logged in
(e.g. via SSH) cause system instability by exploiting either of those
Loongson2F bugs, e.g. by executing a suitably crafted binary?

Thanks in advance for you help,

Sam