linux-kernel - Re: [PATCH v4 2/2] powerpc: Uprobes port to powerpc

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Date:	Thu, 23 Aug 2012 20:06:18 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Michael Ellerman <michael@...erman.id.au>, ananth@...ibm.com,
	ppcdev <linuxppc-dev@...ts.ozlabs.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Anton Blanchard <anton@...ba.org>, peterz@...radead.org,
	oleg@...hat.com, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH v4 2/2] powerpc: Uprobes port to powerpc

On Thu, 2012-08-23 at 11:02 +0530, Srikar Dronamraju wrote:
> > 
> 
> insn is updated/accessed in the arch independent code. Size of
> uprobe_opcode_t could be different for different archs.
> uprobe_opcode_t
> represents the size of the smallest breakpoint instruction for an
> arch.
> 
> Hence u8 works out the best. I know we could still use uprobe_opcode_t
> and achieve the same. In which case, we would have to interpret
> MAX_UINSN_BYTES differently. Do you see any advantages of using
> uprobe_opcode_t instead of u8 across archs?

But don't you actively rely on the fact that on powerpc, unlike x86, you
-can- atomically replace an instruction with a single 32-bit store ?

If you don't you should consider it, and that makes defining this as a
u8 array non-sensical (as is using memcpy)

Ben.


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