[PATCH] powerpc: Instrument Hypervisor Calls
kravetz at us.ibm.com
Sat Aug 26 04:52:40 EST 2006
On Thu, Aug 24, 2006 at 04:55:10PM +1000, Paul Mackerras wrote:
> > + /* calculate address of stat structure */ \
> > + ld r4,STK_PARM(r3)(r1); /* use opcode as */ \
> > + rldicl r4,r4,62,2; /* index into array */ \
> > + mulli r4,r4,HCALL_STAT_SIZE; \
> It's a pity our multiplies are slow (6 cycles). The rldicl would I
> think be more clearly expressed as srdi r4,r4,2. We could use a shift
> and add instead of the multiply if we put a big fat comment in the
> header that defines the structure warning people to adjust the
> assembly if they change the structure. Might not be worth it though.
I would rather keep the multiply and minimal safety it provides when
people change the structure.
> BTW are we going to die horribly if someone uses an hcall greater than
> MAX_HCALL_OPCODES? The hcall functions are available to modules, so
> it would be quite possible for a module to come along and try to use
> some new hcalls that weren't known about when the kernel was built.
Yes, bad things would happen. This is/was a bad assumption on my part
that all callers would pass in valid opcodes. I'll put in a simple check
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