The following is a sketch of how a macro kcalloc could BUILD_BUG_ON for
overflows of two compile-time operands, or call "kcalloc_variable" for
nonconstant arguments. Tested on gcc 4.7.2 only, since it's what I had to
hand. I didn't do any testing beyond checking that fn2 didn't build, and that
fn1/3 had plausible-looking code on x86_64.
typedef unsigned long size_t;
#define SIZE_MAX (~(size_t)0)
typedef int gfp_t;
extern void *kzalloc(size_t n, gfp_t flags);
extern void *kcalloc_variable(size_t n, size_t size, gfp_t flags);
#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
#define kcalloc(n, size, flags) \
__builtin_choose_expr(__builtin_constant_p((n) | (size)), \
( \
BUILD_BUG_ON((n) > SIZE_MAX / (size)), \
kzalloc((n) * (size), (flags)) \
), kcalloc_variable((n), (size), (flags)))
void fn1() { kcalloc(3, 3, 0); }
//void fn2() { kcalloc(2, ~(size_t)0, 0); }// compile-time BUILD_BUG_ON
void fn3(int i) { kcalloc(2, i, 0); }
Jeff
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