Re: [PATCH 0/2] perf probe fixes for ppc64le

From: Michael Ellerman <mpe@ellerman.id.au>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
	Balbir Singh <bsingharora@gmail.com>
Cc: linux-kernel@vger.kernel.org, Mark Wielaard <mjw@redhat.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 0/2] perf probe fixes for ppc64le
Date: Mon, 11 Apr 2016 14:41:46 +1000	[thread overview]
Message-ID: <1460349706.3444.2.camel@ellerman.id.au> (raw)
In-Reply-To: <20160409134239.GL15993@naverao1-tp.in.ibm.com>

On Sat, 2016-04-09 at 19:12 +0530, Naveen N. Rao wrote:
> 
> I suppose this boils down to the quirkiness of ABIv2. Though, in 
> reality, I don't think most users will notice. As I stated above, users 
> will most likely start with the disassembly or debuginfo and this patch 
> ensures there are actually no surprises there.

Yeah it's unfortunate that we have to handle these two cases differently.

But I think you've chosen the right trade off.

When we are just given the name we *must not* use the global entry point,
otherwise the probes will often not hit - because most calls go to the local
entry point and skip the global entry point entirely.

When we're given a name and offset, it's less confusing if we use the global
entry point as the base for the offset calculation.

So for the concept:

Acked-by: Michael Ellerman <mpe@ellerman.id.au>

I don't really know this part of the perf code enough to give you an ack for the
actual changes, I'll leave that to the perf maintainers.

cheers