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coverity: provide Coverity-friendly MIN_CONST and MAX_CONST

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Coverity has problems seeing through __builtin_choose_expr, which
result in it abandoning analysis of later functions that utilize a
definition that used MIN_CONST or MAX_CONST, such as in qemu-file.c:

 50    DECLARE_BITMAP(may_free, MAX_IOV_SIZE);

CID 1429992 (#1 of 1): Unrecoverable parse warning (PARSE_ERROR)1.
expr_not_constant: expression must have a constant value

As has been done in the past (see 07d66672), it's okay to dumb things
down when compiling for static analyzers.  (Of course, now the
syntax-checker has a false positive on our reference to
__COVERITY__...)

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Fixes: CID 1429992, CID 1429995, CID 1429997, CID 1429999
Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <20200629162804.1096180-1-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Eric Blake 2020-06-29 11:28:04 -05:00 committed by Paolo Bonzini
parent b16c0e20c7
commit 6553aa1d11
1 changed files with 14 additions and 7 deletions
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21
include/qemu/osdep.h
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@ -250,7 +250,8 @@ extern int daemon(int, int);
* Note that neither form is usable as an #if condition; if you truly
* need to write conditional code that depends on a minimum or maximum
* determined by the pre-processor instead of the compiler, you'll
* have to open-code it.
* have to open-code it. Sadly, Coverity is severely confused by the
* constant variants, so we have to dumb things down there.
*/
#undef MIN
#define MIN(a, b) \
@ -258,22 +259,28 @@ extern int daemon(int, int);
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) \
#ifdef __COVERITY__
# define MIN_CONST(a, b) ((a) < (b) ? (a) : (b))
# define MAX_CONST(a, b) ((a) > (b) ? (a) : (b))
#else
# define MIN_CONST(a, b) \
__builtin_choose_expr( \
__builtin_constant_p(a) && __builtin_constant_p(b), \
(a) < (b) ? (a) : (b), \
((void)0))
# define MAX_CONST(a, b) \
__builtin_choose_expr( \
__builtin_constant_p(a) && __builtin_constant_p(b), \
(a) > (b) ? (a) : (b), \
((void)0))
#endif
/*
* Minimum function that returns zero only if both values are zero.