[nrf fromtree] lib: os: cbprintf: Reduce stack usage when no optimization

Use single fixed size on stack array instead of compile time fitting.
When compiler is optimizing it can pick smallest array but with no
optimization there is an increased stack usage.

Signed-off-by: Krzysztof Chruscinski <[email protected]>
(cherry picked from commit 1fb8364)
Signed-off-by: Andrzej Głąbek <[email protected]>

Author: nordic-krch

include/zephyr/sys/cbprintf_internal.h

@@ -357,7 +357,15 @@ union z_cbprintf_hdr {
 /* Allocation to avoid using VLA and alloca. Alloc frees space when leaving
  * a function which can lead to increased stack usage if logging is used
  * multiple times. VLA is not always available.
+ *
+ * Use large array when optimization is off to avoid increased stack usage.
  */
+#ifdef CONFIG_NO_OPTIMIZATIONS
+#define Z_CBPRINTF_ON_STACK_ALLOC(_name, _len) \
+	__ASSERT(_len <= 32, "Too many string arguments."); \
+	uint8_t _name##_buf32[32]; \
+	_name = _name##_buf32
+#else
 #define Z_CBPRINTF_ON_STACK_ALLOC(_name, _len) \
 	__ASSERT(_len <= 32, "Too many string arguments."); \
 	uint8_t _name##_buf4[4]; \
@@ -370,6 +378,7 @@ union z_cbprintf_hdr {
 		((_len) <= 12 ? _name##_buf12 : \
 		((_len) <= 16 ? _name##_buf16 : \
 		 _name##_buf32)))
+#endif
 
 /** @brief Statically package a formatted string with arguments.
  *