Re: Switch FPU emulator trap to BREAK instruction

[David Daney <ddaney@caviumnetworks.com>]

Muthu Kumaran wrote:
> I am using 2.6.18 linux version on MIPS32 core. One of the application
> is using intensive floating point operations. This hardware doesn't
> have FPU and also the application is not compiled for software
> floating point support.
> Hence, it is using the floating point emulation.
>
> While running that application, On a timer interrupt there is a normal
> integer div instruction which gives wrong result in the HI register.
>
> However, when I applied the following patch, this problem disappeared.
>
> http://kerneltrap.org/mailarchive/git-commits-head/2008/10/30/3873324
>
> When I looked into the patch, handling of invalid instruction
> exception is moved from trap to break.
Incorrect analysis.  It was changed from an Adress Error (ADE) exception 
to a BREAK.

> There is no other behavioural change in this patch. I really don't
> understand the need for this patch, May I ask someone to explain the
> background information behind this patch? Is this for any known issue?
The change log states the reason.  FPU emulator delay slot emulation was 
failing on some systems.

David Daney