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From: Markus Armbruster <armbru@redhat.com>
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Date: Mon, 10 Mar 2014 19:21:51 +0100
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	(Peter Maydell's message of "Mon, 10 Mar 2014 13:41:31 +0000")
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Subject: Re: [Qemu-devel] test-qapi-visit causes clang -fsanitize=undefined
	warning
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Luiz Capitulino <lcapitulino@redhat.com>

Peter Maydell <peter.maydell@linaro.org> writes:

> On 10 March 2014 13:36, Markus Armbruster <armbru@redhat.com> wrote:
>> Peter Maydell <peter.maydell@linaro.org> writes:
>> Turns out my clang installation doesn't support -fsanitize=undefined: it
>> lacks libclang_rt.san-x86_64.a.
>>
>> Test works fine without -fsanitize=undefined.  I set a breakpoint on
>> visit_type_UserDefA_fields, and there's no null pointer to be found.
>
> Yes, there is. This is gdb on a gcc-compiled version of
> the test:
>
> /visitor/input-strict/fail/union-flat:
> Breakpoint 1, visit_type_UserDefA_fields (m=0x5555557a8ed0,
> obj=0x5555557a8d88, errp=0x7fffffffdfb0)
>     at tests/test-qapi-visit.c:460
> 460     {
> (gdb) print *obj
> $3 = (UserDefA *) 0x0
> (gdb) bt
> #0  visit_type_UserDefA_fields (m=0x5555557a8ed0, obj=0x5555557a8d88,
> errp=0x7fffffffdfb0)
>     at tests/test-qapi-visit.c:460
> #1  0x000055555555b2a2 in visit_type_UserDefFlatUnion
> (m=0x5555557a8ed0, obj=0x7fffffffdfd8, name=0x0, errp=0x0)
>     at tests/test-qapi-visit.c:654
> #2  0x0000555555558c0b in qapi_free_UserDefFlatUnion
> (obj=0x5555557a8d80) at tests/test-qapi-types.c:368
> #3  0x000055555555cc47 in test_validate_fail_union_flat
> (data=0x5555557a8de0, unused=0x7fffffffe3f0)
>     at
> /home/petmay01/linaro/qemu-from-laptop/qemu/tests/test-qmp-input-strict.c:241
>
> *obj is NULL, which is what clang is complaining about.

I think what happens here is the visitor fails half-way through
constructing the type, and returns a UserDefFlatUnion with kind
USER_DEF_UNION_KIND_A and data.a null, violating the data type's
invariant.

We either have to relax the invariant, or fix the error paths.  I'm
looking into the latter.