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qapi: Document shortcoming with union 'data' branch 

Add a FIXME to remind us to fully audit whether removing the
'void *data' branch of each qapi union type can be done safely.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1438297637-26789-1-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
master
Eric Blake 2015-07-30 17:07:17 -06:00 committed by Markus Armbruster
parent 2f52e20597
commit ca56a822dd
1 changed files with 8 additions and 0 deletions
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8
scripts/qapi-types.py
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@ -219,6 +219,14 @@ struct %(name)s
''',
discriminator_type_name=c_name(discriminator_type_name))
# FIXME: What purpose does data serve, besides preventing a union that
# has a branch named 'data'? We use it in qapi-visit.py to decide
# whether to bypass the switch statement if visiting the discriminator
# failed; but since we 0-initialize structs, and cannot tell what
# branch of the union is in use if the discriminator is invalid, there
# should not be any data leaks even without a data pointer. Or, if
# 'data' is merely added to guarantee we don't have an empty union,
# shouldn't we enforce that at .json parse time?
ret += mcgen('''
union { /* union tag is @%(c_name)s */
void *data;