kernel: Option to not use tls to get current thread

Add a Kconfig option to tell whether or not using thread
local storage to store current thread.

The function using it can be called from ISR and using
TLS variables in this context may (should ???) not be
allowed

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>

include/zephyr/kernel.h

@@ -596,7 +596,8 @@ __syscall k_tid_t k_sched_current_thread_query(void);
 __attribute_const__
 static inline k_tid_t k_current_get(void)
 {
-#ifdef CONFIG_THREAD_LOCAL_STORAGE
+#ifdef CONFIG_CURRENT_THREAD_USE_TLS
+
 	/* Thread-local cache of current thread ID, set in z_thread_entry() */
 	extern __thread k_tid_t z_tls_current;
 

kernel/Kconfig

@@ -288,6 +288,20 @@ config ERRNO_IN_TLS
 	  Use thread local storage to store errno instead of storing it in
 	  the kernel thread struct. This avoids a syscall if userspace is enabled.
 
+config CURRENT_THREAD_USE_NO_TLS
+	bool
+	help
+	  Hidden symbol to not use thread local storage to store current
+	  thread.
+
+config CURRENT_THREAD_USE_TLS
+	bool "Store current thread in thread local storage (TLS)"
+	depends on THREAD_LOCAL_STORAGE && !CURRENT_THREAD_USE_NO_TLS
+	default y
+	help
+	  Use thread local storage to store the current thread. This avoids a
+	  syscall if userspace is enabled.
+
 choice SCHED_ALGORITHM
 	prompt "Scheduler priority queue algorithm"
 	default SCHED_DUMB

lib/os/thread_entry.c

@@ -12,7 +12,7 @@
  */
 
 #include <zephyr/kernel.h>
-#ifdef CONFIG_THREAD_LOCAL_STORAGE
+#ifdef CONFIG_CURRENT_THREAD_USE_TLS
 #include <zephyr/random/random.h>
 
 __thread k_tid_t z_tls_current;
@@ -35,7 +35,7 @@ extern __thread volatile uintptr_t __stack_chk_guard;
 FUNC_NORETURN void z_thread_entry(k_thread_entry_t entry,
 				 void *p1, void *p2, void *p3)
 {
-#ifdef CONFIG_THREAD_LOCAL_STORAGE
+#ifdef CONFIG_CURRENT_THREAD_USE_TLS
 	z_tls_current = k_sched_current_thread_query();
 #endif
 #ifdef CONFIG_STACK_CANARIES_TLS