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Re: [Qemu-devel] [PATCH] Permit zero-sized qemu_malloc() & friends


From: Blue Swirl
Subject: Re: [Qemu-devel] [PATCH] Permit zero-sized qemu_malloc() & friends
Date: Mon, 7 Dec 2009 20:12:57 +0200

On Mon, Dec 7, 2009 at 5:50 PM, Anthony Liguori <address@hidden> wrote:
> Markus Armbruster wrote:
>>
>> Commit a7d27b53 made zero-sized allocations a fatal error, deviating
>> from ISO C's malloc() & friends.  Revert 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 to
> capture some action items from the discussion that I think there is
> agreement about.  Since 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 return
> malloc(1) when size=0 only for production builds (via
> --enable-zero-mallocs).  Development trees will maintain their current
> 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.  I'm not tied to them.
>
> Will do our best to convert old code to use these functions where ever
> possible.  New code will be required to use these functions unless not
> possible.  n_types==0 is valid.  sizeof(type)==0 is valid.  Both
> circumstances return a unique non-NULL pointer.  If memory allocation fails,
> execution will abort.
>
> The existing qemu_malloc() will maintain it's current behavior (with the
> exception of the relaxed size==0 assertion for production releases).
>
> Does anyone object to this moving forward?

Excellent plan.




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