https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116016
Alejandro Colomar <alx at kernel dot org> changed:
What |Removed |Added
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CC| |alx at kernel dot org
--- Comment #49 from Alejandro Colomar <alx at kernel dot org> ---
For reading the counted_by value, that is, for reading the number of elements
in the FAM, I'm implementing a __lengthof__ operator, which returns the value
that the typical ARRAY_SIZE() macro returns, but also works with FAMs declared
with this attribute (and I also want to make it work on function parameters
declared as arrays).
Consider that for your design of a builtin for setting the counted_by value,
since you don't need to have a built-in for reading the value. ;)
<https://inbox.sourceware.org/gcc-patches/p33myw2zqvtysc3ayfygcvarw4ka3wwltycqjyehdgy64wsgug@ewi3uvid6rrb/T/>
That is, __lengthof__ should be useful in all of the following cases:
#define memberof(T, m) (((T *) NULL)->m)
struct s {
size_t n;
int fam[] __attribute__((counted_by(n)));
};
__attribute__((access(read_only, 3, 4)))
void
f(size_t n1, int p[n1], int q[], size_t n2)
{
int a[3];
size_t m;
struct s *s;
m = offsetof(struct s, fam) + sizeof(memberof(struct s, fam)[0]) * 7;
s = malloc(m);
assert(__lengthof__(a) == 3);
assert(__lengthof__(p) == n1);
assert(__lengthof__(q) == n2);
assert(__lengthof__(memberof(struct s, fam)) == m);
}
