Hi Stefano,
On 07/05/2020 21:34, Stefano Stabellini wrote:
On Thu, 7 May 2020, Julien Grall wrote:
Hi,
On 07/05/2020 21:29, Stefano Stabellini wrote:
#define read_atomic(p) ({
\
- typeof(*p) __x; \
- switch ( sizeof(*p) ) { \
- case 1: __x = (typeof(*p))read_u8_atomic((uint8_t *)p); break; \
- case 2: __x = (typeof(*p))read_u16_atomic((uint16_t *)p); break; \
- case 4: __x = (typeof(*p))read_u32_atomic((uint32_t *)p); break; \
- case 8: __x = (typeof(*p))read_u64_atomic((uint64_t *)p); break; \
- default: __x = 0; __bad_atomic_size(); break; \
- } \
- __x; \
+ union { typeof(*p) val; char c[0]; } x_; \
+ read_atomic_size(p, x_.c, sizeof(*p)); \
Wouldn't it be better to pass x_ as follows:
read_atomic_size(p, &x_, sizeof(*p));
I am not sure to understand this. Are you suggesting to pass a pointer to the
union?
Yes. Would it cause a problem that I couldn't spot?
You defeat the purpose of an union by casting it to something else (even
if it is void *).
The goal of the union is to be able to access a value in different way
through a member. So x_.c is more union friendly and makes easier to
understand why it was implemented like this.
Cheers,
--
Julien Grall
