On Fri, 26 Jun 2020 at 14:57, Paolo Bonzini <pbonz...@redhat.com> wrote:
>
> From: Eric Blake <ebl...@redhat.com>
>
> I'm not aware of any immediate bugs in qemu where a second runtime
> evaluation of the arguments to MIN() or MAX() causes a problem, but
> proactively preventing such abuse is easier than falling prey to an
> unintended case down the road. At any rate, here's the conversation
> that sparked the current patch:
> https://lists.gnu.org/archive/html/qemu-devel/2018-12/msg05718.html
Hi; the changes in this patch seem to confuse Coverity.
> +#undef MIN
> +#define MIN(a, b) \
> + ({ \
> + typeof(1 ? (a) : (b)) _a = (a), _b = (b); \
> + _a < _b ? _a : _b; \
> + })
> +#define MIN_CONST(a, b) \
> + __builtin_choose_expr( \
> + __builtin_constant_p(a) && __builtin_constant_p(b), \
> + (a) < (b) ? (a) : (b), \
> + ((void)0))
> +#undef MAX
> +#define MAX(a, b) \
> + ({ \
> + typeof(1 ? (a) : (b)) _a = (a), _b = (b); \
> + _a > _b ? _a : _b; \
> + })
> +#define MAX_CONST(a, b) \
> + __builtin_choose_expr( \
> + __builtin_constant_p(a) && __builtin_constant_p(b), \
> + (a) > (b) ? (a) : (b), \
> + ((void)0))
In particular, where MIN_CONST or MAX_CONST are used to
define values that must be const, eg in qemu-file.c:
50 DECLARE_BITMAP(may_free, MAX_IOV_SIZE);
or in hcd-xhci.h:
217 USBPort uports[MAX_CONST(MAXPORTS_2, MAXPORTS_3)];
Coverity reports:
CID 1429992 (#1 of 1): Unrecoverable parse warning (PARSE_ERROR)1.
expr_not_constant: expression must have a constant value
Can we do something (eg providing fallback less-intelligent
versions of the macro ifdef __COVERITY__) to help it?
(This is the cause of CID 1429992, 1429995, 1429997,
1429999. Parse errors are unfortunate because Coverity
abandons analysis of the affected function entirely,
and analysis of its callers is also limited.)
thanks
-- PMM
