[PATCH v4] Fixups of Loongson2F

[Sam Kuper]

Anyone? (Optimistically CC'ing gnewsense-users, too!)

N.B. Wu Zhangjin's original email, to which my questions below are a
reply, can be seen in the binutils mailing list archive here:
http://sourceware.org/ml/binutils/2009-11/msg00387.html

Regards,

Sam

On 02/01/2014, Sam Kuper <sam.kuper@uclmail.net> wrote:
> 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