Re: [Qemu-devel] [PATCH v11 22/28] qapi: Simplify visiting of alternate types

[Eric Blake <eblake@redhat.com>]

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On 11/10/2015 11:51 PM, Eric Blake wrote:
> Previously, working with alternates required two lookup arrays
> and some indirection: for type Foo, we created Foo_qtypes[]
> which maps each qtype to a value of the generated FooKind enum,
> then look up that value in FooKind_lookup[] like we do for other
> union types.
> 
> This has a couple of subtle bugs.  First, the generator was
> creating a call with a parameter '(int *) &(*obj)->type' where
> type is an enum type; this is unsafe if the compiler chooses
> to store the enum type in a different size than int, where
> assigning through the wrong size pointer can corrupt data or
> cause a SIGBUS.

Yuck - we still have this bug for enums:

> void visit_type_OnOffAuto(Visitor *v, OnOffAuto *obj, const char *name, Error **errp)
> {
> visit_type_enum(v, (int *)obj, OnOffAuto_lookup, "OnOffAuto", name, errp);
> }

I guess I just added more work to my plate.

But at the same time, no one has complained of the (int*)Enum causing
SIGBUS on any of our platforms for either enums or alternates, so while
we are doing gross things, I don't think we have to rush a fix into 2.5
for this particular bug.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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