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>Some Basic Rules</H1
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>No memory protection</DT
><DD
><P
> If you corrupt memory, whether in user context or
interrupt context, the whole machine will crash. Are you
sure you can't do what you want in userspace?
</P
></DD
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>No floating point or <SPAN
CLASS="ACRONYM"
>MMX</SPAN
></DT
><DD
><P
> The <SPAN
CLASS="ACRONYM"
>FPU</SPAN
> context is not saved; even in user
context the <SPAN
CLASS="ACRONYM"
>FPU</SPAN
> state probably won't
correspond with the current process: you would mess with some
user process' <SPAN
CLASS="ACRONYM"
>FPU</SPAN
> state. If you really want
to do this, you would have to explicitly save/restore the full
<SPAN
CLASS="ACRONYM"
>FPU</SPAN
> state (and avoid context switches). It
is generally a bad idea; use fixed point arithmetic first.
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>A rigid stack limit</DT
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><P
> The kernel stack is about 6K in 2.2 (for most
architectures: it's about 14K on the Alpha), and shared
with interrupts so you can't use it all. Avoid deep
recursion and huge local arrays on the stack (allocate
them dynamically instead).
</P
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>The Linux kernel is portable</DT
><DD
><P
> Let's keep it that way. Your code should be 64-bit clean,
and endian-independent. You should also minimize CPU
specific stuff, e.g. inline assembly should be cleanly
encapsulated and minimized to ease porting. Generally it
should be restricted to the architecture-dependent part of
the kernel tree.
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