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Date: Mon, 29 Nov 2010 12:52:33 +0530
From: "K.Prasad" <prasad@linux.vnet.ibm.com>
To: Andreas Schwab <schwab@linux-m68k.org>
Subject: Re: ppc_set_hwdebug vs ptrace_set_debugreg
Message-ID: <20101129072233.GA15560@in.ibm.com>
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Cc: linuxppc-dev@ozlabs.org, Dave Kleikamp <shaggy@linux.vnet.ibm.com>
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On Sat, Nov 27, 2010 at 08:36:30PM +0100, Andreas Schwab wrote:
> Why does ptrace_set_debugreg call register_user_hw_breakpoint, but
> ppc_set_hwdebug doesn't?  Shouldn't ppc_set_hwdebug set the
> DABR_DATA_(READ|WRITE|TRANSLATION) bits in the dabr?
> 
> Andreas.

The hw-breakpoint interfaces were initially planned for the old ptrace
option PTRACE_SET_DEBUGREG,while, the newer ptrace options are mostly
to exploit the advanced debug features of Book3E processors.

Although ppc_set_hwdebug() can set DABR through set_dabr() in
arch/powerpc/kernel/process.c, it is good to have it converted to use
register_user_hw_breakpoint(). This was planned to be done alongside the
conversion of all ptrace options enabled by CONFIG_PPC_ADV_DEBUG_REGS,
which is yet to be done.

Are you looking to use debug registers through perf, or somesuch, that
you need register_user_hw_breakpoint() to be used for these new ptrace
flags?

Thanks,
K.Prasad