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From: Blue Swirl <blauwirbel@gmail.com>
Date: Mon, 7 Dec 2009 20:12:57 +0200
Message-ID: <f43fc5580912071012l53b6d34y4f64c1a2268fe64e@mail.gmail.com>
Subject: Re: [Qemu-devel] [PATCH] Permit zero-sized qemu_malloc() & friends
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To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org, Avi Kivity <avi@redhat.com>, Markus Armbruster <armbru@redhat.com>, Paul Brook <paul@codesourcery.com>

On Mon, Dec 7, 2009 at 5:50 PM, Anthony Liguori <anthony@codemonkey.ws> wro=
te:
> Markus Armbruster wrote:
>>
>> Commit a7d27b53 made zero-sized allocations a fatal error, deviating
>> from ISO C's malloc() & friends. =C2=A0Revert that, but take care never =
to
>> return a null pointer, like malloc() & friends may do (it's
>> implementation defined), because that's another source of bugs.
>>
>
> While it's always fun to argue about standards interpretation, I wanted t=
o
> capture some action items from the discussion that I think there is
> agreement about. =C2=A0Since I want to make changes for 0.12, I think it =
would be
> best to try and settle these now so we can do this before -rc2.
>
> For 0.12.0-rc2:
>
> I will send out a patch tonight or tomorrow changing qemu_malloc() to ret=
urn
> malloc(1) when size=3D0 only for production builds (via
> --enable-zero-mallocs). =C2=A0Development trees will maintain their curre=
nt
> behavior.
>
> For 0.13:
>
> Someone (Marcus?) will introduce four new allocation functions.
>
> type *qemu_new(type, n_types);
> type *qemu_new0(type, n_types);
>
> type *qemu_renew(type, mem, n_types);
> type *qemu_renew0(type, mem, n_types);
>
> NB: The names are borrowed from glib. =C2=A0I'm not tied to them.
>
> Will do our best to convert old code to use these functions where ever
> possible. =C2=A0New code will be required to use these functions unless n=
ot
> possible. =C2=A0n_types=3D=3D0 is valid. =C2=A0sizeof(type)=3D=3D0 is val=
id. =C2=A0Both
> circumstances return a unique non-NULL pointer. =C2=A0If memory allocatio=
n fails,
> execution will abort.
>
> The existing qemu_malloc() will maintain it's current behavior (with the
> exception of the relaxed size=3D=3D0 assertion for production releases).
>
> Does anyone object to this moving forward?

Excellent plan.