Daniele,
Thanks for spotting these. GCC error message may be cryptic, but using an
atomic variable as the return value is an error regardless.
Acked-by: Jarno Rajahalme <jrajaha...@nicira.com>
Pushed to master,
Jarno
On Aug 6, 2014, at 10:35 AM, Daniele Di Proietto <ddiproie...@vmware.com> wrote:
> There's no reason for the local variable 'old_count' to be atomic. In fact, if
> it is atomic it triggers a GCC4.9 warning (Wunused-value)
> The global variables 'a' and 'paux' could be static, according to sparse.
>
> Signed-off-by: Daniele Di Proietto <ddiproie...@vmware.com>
> ---
> There's something interesting about the warning: GCC does not complain about
> 'old_count' being atomic, but about "right-hand operand of comma expression
> having no effect" (the comma comes from OVS macro atomic_add_explicit()).
>
> I've isolated a test case to trigger the warning:
>
> /* main.c */
> #include <stdatomic.h>
> #include <stdint.h>
>
> int main()
> {
> _Atomic(uint32_t) a = 0;
> #ifdef TEST_ATOMIC_DST
> _Atomic(uint32_t) b = 0;
> #else
> uint32_t b = 0;
> #endif
> b = atomic_fetch_add_explicit ((&a), (1), (memory_order_seq_cst)),
> (void) 0;
>
> return b;
> }
>
> When compiled with
>
> gcc main.c -Wall
>
> there's no warning. When compiled with
>
> gcc main.c -Wall -DTEST_ATOMIC_DST
>
> GCC complains with
>
> main.c: In function ‘main’:
> main.c:13:70: warning: right-hand operand of comma expression has no effect
> [-Wunused-value]
> b = atomic_fetch_add_explicit ((&a), (1), (memory_order_seq_cst)),
> ^
> I'm using gcc (Debian 4.9.1-1) 4.9.1
> ---
> tests/test-atomic.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/tests/test-atomic.c b/tests/test-atomic.c
> index ca293ba..31c06fa 100644
> --- a/tests/test-atomic.c
> +++ b/tests/test-atomic.c
> @@ -167,7 +167,7 @@ test_atomic_flag(void)
> ovs_assert(atomic_flag_test_and_set(&flag) == false);
> }
>
> -uint32_t a;
> +static uint32_t a;
>
> struct atomic_aux {
> atomic_uint32_t count;
> @@ -175,7 +175,7 @@ struct atomic_aux {
> ATOMIC(uint32_t *) data;
> };
>
> -ATOMIC(struct atomic_aux *) paux = ATOMIC_VAR_INIT(NULL);
> +static ATOMIC(struct atomic_aux *) paux = ATOMIC_VAR_INIT(NULL);
> static struct atomic_aux *auxes = NULL;
>
> #define ATOMIC_ITEM_COUNT 1000000
> @@ -273,7 +273,7 @@ static void *
> atomic_writer(void *aux_)
> {
> struct atomic_aux *aux = aux_;
> - atomic_uint32_t old_count;
> + uint32_t old_count;
> uint32_t *data;
> size_t i;
>
> --
> 2.0.1
>
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