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From: =?utf-8?Q?Llu=C3=ADs_Vilanova?= <vilanova@ac.upc.edu>
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Date: Wed, 10 Feb 2016 14:15:24 +0100
In-Reply-To: <56BAAD86.3010007@twiddle.net> (Richard Henderson's message of
	"Wed, 10 Feb 2016 14:24:54 +1100")
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Subject: Re: [Qemu-devel] [PATCH v6 3/4] tcg: Add type for vCPU pointers
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To: Richard Henderson <rth@twiddle.net>
Cc: Peter Maydell <peter.maydell@linaro.org>, Eduardo Habkost <ehabkost@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Anthony Green <green@moxielogic.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>, Blue Swirl <blauwirbel@gmail.com>, Max Filippov <jcmvbkbc@gmail.com>, Michael Walle <michael@walle.cc>, "open list:ARM" <qemu-arm@nongnu.org>, "open
	list:PowerPC" <qemu-ppc@nongnu.org>, Leon Alrae <leon.alrae@imgtec.com>, Bastian Koppelmann <kbastian@mail.uni-paderborn.de>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Guan Xuetao <gxt@mprc.pku.edu.cn>, Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>, Aurelien Jarno <aurelien@aurel32.net>, Jia Liu <proljc@gmail.com>

Richard Henderson writes:

> On 02/10/2016 08:14 AM, Llu=C3=ADs Vilanova wrote:
>> Adds the 'TCGv_env' type for pointers to 'CPUArchState' objects. The
>> tracing infrastructure later needs to differentiate between regular
>> pointers and pointers to vCPUs.
>>=20
>> Also changes all targets to use the new 'TCGv_cpu' type instead of the
>> generic 'TCGv_ptr'. As of now, the change is merely cosmetic ('TCGv_env'
>> translates into 'TCGv_ptr'), but that could change in the future to
>> enforce the difference.

> I suppose.

> We won't be able distinguish TCGv_env from TCGv_ptr until env can be
> auto-converted to ptr.  Which I can't imagine happening without switching=
 to
> C++.

It's difficult to differenciate between TCGv_ptr and TCGv_env in "tcg/tcg-o=
p.h"
unless an explicit operation is added to perform casts or to get a TCGv_ptr=
 from
a TCGv_env+offset (e.g., add a tcg_gen_env_ld8u_i32 built on top of
tcg_gen_ld8u_i32). That is, unless QEMU switches to C++.

But types could be easily enforced in helper declarations, which can intern=
ally
cast to the pointer type.

As a side note, I've just spotted a typo in the commit message (TCGv_cpu ->
TCGv_env).


> I see your motivation in 4/4, so I guess this is fine.

> Acked-by: Richard Henderson <rth@twiddle.net>

Thanks,
  Lluis