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Date: Fri, 25 Aug 2017 20:34:54 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20170826003454.GA23546@flamenco>
References: <150142369849.12995.11229612194223213120.stgit@frigg.lan>
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Subject: Re: [Qemu-devel] [PATCH v8 0/5] hypertrace: Lightweight
 guest-to-QEMU trace channel
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To: =?iso-8859-1?Q?Llu=EDs?= Vilanova <vilanova@ac.upc.edu>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, Luiz Capitulino <lcapitulino@redhat.com>

On Sun, Jul 30, 2017 at 17:08:18 +0300, Lluís Vilanova wrote:
> The hypertrace channel allows guest code to emit events in QEMU (the host) using
> its tracing infrastructure (see "docs/trace.txt"). This works in both 'system'
> and 'user' modes, is architecture-agnostic and introduces minimal noise on the
> guest.
> 
> See first commit for a full description, use-cases and an example.
> 
> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>

This would be indeed very useful once TCG instrumentation is in place.

However, I'm not very excited about this being PCI-only and Linux-only for
system mode
I wonder how we could make this work on all hosts -- did you consider using
"magic" instructions? We'd need a different magic instruction for each
guest ISA, but the library would hide that anyway (and the library code
would be the same for user and system modes).

Thanks,

		Emilio