Re: [PATCH v3 3/9] powerpc/kprobes/optprobes: Move over to patch_instruction

On 2017/06/07 03:46PM, Balbir Singh wrote:

On Wed, 2017-06-07 at 00:42 +0530, Naveen N. Rao wrote:

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On 2017/06/06 02:29PM, Balbir Singh wrote:

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With text moving to read-only migrate optprobes to using
the patch_instruction infrastructure. Without this optprobes
will fail and complain.

<snip>

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+	/* We can optimize this via patch_instruction_window later */

This probably needs a TODO just so it's clear. I do think this would be 
good to add since we copy many instructions while setting up the 
optprobe, so this is quite slow as it exists today.

I made it read like a TODO, with a TOOD:

Yes, just a nit that it would be good to have an explicit 'TODO:' there, 
without which it looks like any other comment...

But, thinking about this more, we could probably simplify this by having 
optprobes set things up in a local buffer before copying it into the 
instruction slot. That will also make it easier for the subsequent 
support to patch many instructions at once.

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+	size = (TMPL_END_IDX * sizeof(kprobe_opcode_t)) / sizeof(int);

That's just TMPL_END_IDX.

The entire kprobe_opcode_t and int types thing is a bit messy. The size

Right - it's an artifact of kprobes generic infrastructure. For powerpc, 
it's always an integer.

calculation assumes nothing for now in terms of sizes, but I guess the
patch_instruction does. Another TODO?

Not sure I follow...


- Naveen