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From: Roland McGrath <roland@redhat.com>
To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
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Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
        Steven Rostedt <rostedt@goodmis.org>,
        Arnaldo Carvalho de Melo <acme@infradead.org>,
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Subject: Re: [RFC] [PATCH 2.6.37-rc5-tip 13/20] 13: x86: x86 specific probe
 handling
In-Reply-To: Srikar Dronamraju's message of  Friday, 28 January 2011 10:27:21 +0530 <20110128045721.GV19725@linux.vnet.ibm.com>
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Date: Thu, 27 Jan 2011 22:23:16 -0800 (PST)
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> Uprobes doesn't request/handle block-step for now. So can we postpone
> your suggested changes till uprobes needs to handle block-step?

That's not the issue.  The way the hardware works is that if the bit is set
in the MSR, then the TF eflags bit means block-step instead of single-step.
So if PTRACE_SINGLEBLOCK has been used (i.e. user_enable_block_step), then
this can interfere with your use of single-step.  You need to do the work
in the else branch of step.c:enable_step to ensure that the hardware is not
left in the state where it will do block-step instead of single-step when
uprobes wants a single-step done.


Thanks,
Roland