kernel: Fixed init_delay initialization on older GCC versions

Within the K_THREAD_DEFINE macro, a nested set of macros is expanded to
populate the values of a global _static_thread_data structure.

The K_THREAD_DEFINE macro expands to statements including the
Z_THREAD_COMMON_DEFINE macro, which expands to statements including the
Z_THREAD_INITIALIZER macro, which expands to an initialization expression
of a _static_thread_data struct. The init_delay member of that struct is
then initialized with the Z_THREAD_INIT_DELAY_INITIALIZER macro, which
expands to an expression including the SYS_TIMEOUT_MS macro which
converts a number of milliseconds to a number of ticks.

For example, take the following macro:

    K_THREAD_DEFINE(
        thread_X,
        STACKSIZE,
        thread_X_entry_point, NULL, NULL, NULL,
        PRIORITY,
        0,
        0);

In abbreviated form, it expands as follows:

    typedef struct {
        int ticks;
    } k_timeout_t;

    struct _static_thread_data {
        /* ... */
        k_timeout_t init_delay;
    };

    struct _static_thread_data _k_thread_data_thread_X = {
        /* ... */
        .init_delay = (k_timeout_t){ .ticks = 0 }
    };

However, in GCC versions before 5.1, the code fails to compile with the
error "initializer element is not constant", when compiled with the
following options:

    gcc -std=gnu99 -c test.c

In the above code, the error can be corrected by replacing...

    .init_delay = (k_timeout_t){ .ticks = 0 }

...with...

    .init_delay = { .ticks = 0 }

...i.e. removing initialization with a compound literal.

In order to achieve this, this patch reworks the system of macros.

The Z_TIMEOUT_TICKS(t) macro is refactored into Z_TIMEOUT_TICKS_INIT(t)
which defines the initializer part: { .ticks = t }, and Z_TIMEOUT_TICKS(t)
which is defined as ((k_timeout_t) Z_TIMEOUT_TICKS_INIT(t)) .

For symmetry, Z_TIMEOUT_NO_WAIT_INIT is split out of Z_TIMEOUT_NO_WAIT.

Similarly, SYS_TIMEOUT_MS_INIT(ms) is split out of SYS_TIMEOUT_MS(ms) so
that the Z_THREAD_INIT_DELAY_INITIALIZER(ms) macro can use
SYS_TIMEOUT_MS_INIT(ms) which expands Z_TIMEOUT_TICKS_INIT(t) to initialize
init_delay without using a compound literal.

Signed-off-by: Joel Holdsworth <jholdsworth@nvidia.com>

include/zephyr/kernel.h

@@ -756,7 +756,7 @@ struct _static_thread_data {
 #define Z_THREAD_INIT_DELAY_INITIALIZER(ms) .init_delay_ms = (ms)
 #define Z_THREAD_INIT_DELAY(thread) SYS_TIMEOUT_MS((thread)->init_delay_ms)
 #else
-#define Z_THREAD_INIT_DELAY_INITIALIZER(ms) .init_delay = SYS_TIMEOUT_MS(ms)
+#define Z_THREAD_INIT_DELAY_INITIALIZER(ms) .init_delay = SYS_TIMEOUT_MS_INIT(ms)
 #define Z_THREAD_INIT_DELAY(thread) (thread)->init_delay
 #endif
 

include/zephyr/sys/time_units.h

@@ -38,10 +38,16 @@ extern "C" {
  */
 #define SYS_FOREVER_US (-1)
 
+/** @brief System-wide macro to initialize #k_timeout_t with a number of ticks
+ * converted from milliseconds.
+ */
+#define SYS_TIMEOUT_MS_INIT(ms) \
+	Z_TIMEOUT_TICKS_INIT((ms) == SYS_FOREVER_MS ? \
+	K_TICKS_FOREVER : Z_TIMEOUT_MS_TICKS(ms))
+
 /** @brief System-wide macro to convert milliseconds to kernel timeouts
  */
-#define SYS_TIMEOUT_MS(ms) Z_TIMEOUT_TICKS((ms) == SYS_FOREVER_MS ? \
-					   K_TICKS_FOREVER : Z_TIMEOUT_MS_TICKS(ms))
+#define SYS_TIMEOUT_MS(ms) ((k_timeout_t) SYS_TIMEOUT_MS_INIT(ms))
 
 /* Exhaustively enumerated, highly optimized time unit conversion API */
 

include/zephyr/sys_clock.h

@@ -115,12 +115,14 @@ typedef struct {
 /** @} */
 
 /** @cond INTERNAL_HIDDEN */
-#define Z_TIMEOUT_NO_WAIT ((k_timeout_t) {0})
+#define Z_TIMEOUT_NO_WAIT_INIT {0}
+#define Z_TIMEOUT_NO_WAIT ((k_timeout_t) Z_TIMEOUT_NO_WAIT_INIT)
 #if defined(__cplusplus) && ((__cplusplus - 0) < 202002L)
-#define Z_TIMEOUT_TICKS(t) ((k_timeout_t) { (t) })
+#define Z_TIMEOUT_TICKS_INIT(t) { (t) }
 #else
-#define Z_TIMEOUT_TICKS(t) ((k_timeout_t) { .ticks = (t) })
+#define Z_TIMEOUT_TICKS_INIT(t) { .ticks = (t) }
 #endif
+#define Z_TIMEOUT_TICKS(t) ((k_timeout_t) Z_TIMEOUT_TICKS_INIT(t))
 #define Z_FOREVER Z_TIMEOUT_TICKS(K_TICKS_FOREVER)
 
 #ifdef CONFIG_TIMEOUT_64BIT