Re: Anyone working on ftrace function graph support on ARM?

Tim Bird
2009-03-24T21:40:44Z

Frederic Weisbecker wrote:
> Yes, ie:
>
> _Before jumping to the function entry hook, you must save
> the arguments for the traced function on the stack.
> On x86, its eax, edx and ecx.
> On arm, it will be r0-r3.
> Then you have to transmit the address of the traced function
> (it's on r14) and it's parent (must rely on fp for that).
> Then you call the entry hook and restore the old scratch/arg
> registers.
>
>
> _ On return hook it's pretty the same, (saving the scratch
> registers, especially the return value which should be on r0
> and r1 if I'm not wrong).
> But you'll have to get the original return address from the
> return handler and then put it on pc.
>
> Well it's a very naive listing, there are sometimes some problems.
> For example on x86-64, I had to save even some non-scratch registers
> before calling the return hook, I still don't know why.

Thanks - this is very helpful. I'll send patches around when
I get something going. Hopefully in the next week or two.
-- Tim

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Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
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