arch/nios2: rearrange for standard use of extern "C"

Consistently place C++ use of extern "C" after all include directives,
within the negative branch of _ASMLANGUAGE if used.

Remove extern "C" support from files that don't declare objects or
functions.

Background from issue #17997:

Declarations that use C linkage should be placed within extern "C"
so the language linkage is correct when the header is included by
a C++ compiler.

Similarly #include directives should be outside the extern "C" to
ensure the language-specific default linkage is applied to any
declarations provided by the included header.

See: https://en.cppreference.com/w/cpp/language/language_linkage
Signed-off-by: Peter Bigot <[email protected]>

Author: pabigot

arch/nios2/include/kernel_arch_data.h

@@ -21,23 +21,11 @@
 #ifndef ZEPHYR_ARCH_NIOS2_INCLUDE_KERNEL_ARCH_DATA_H_
 #define ZEPHYR_ARCH_NIOS2_INCLUDE_KERNEL_ARCH_DATA_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <toolchain.h>
 #include <linker/sections.h>
 #include <arch/cpu.h>
 #include <kernel_arch_thread.h>
 
-#ifndef _ASMLANGUAGE
-#include <kernel.h>
-#include <kernel_internal.h>
-#include <zephyr/types.h>
-#include <sys/util.h>
-#include <sys/dlist.h>
-#endif
-
 /* stacks */
 
 #define STACK_ALIGN_SIZE 4
@@ -47,12 +35,22 @@ extern "C" {
 
 #ifndef _ASMLANGUAGE
 
-extern K_THREAD_STACK_DEFINE(_interrupt_stack, CONFIG_ISR_STACK_SIZE);
+#include <kernel.h>
+#include <kernel_internal.h>
+#include <zephyr/types.h>
+#include <sys/util.h>
+#include <sys/dlist.h>
 
-#endif /* _ASMLANGUAGE */
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern K_THREAD_STACK_DEFINE(_interrupt_stack, CONFIG_ISR_STACK_SIZE);
 
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_ARCH_NIOS2_INCLUDE_KERNEL_ARCH_DATA_H_ */

include/arch/nios2/arch.h

@@ -22,17 +22,16 @@
 #include <arch/common/sys_io.h>
 #include <arch/common/ffs.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #define STACK_ALIGN  4
 
 #ifndef _ASMLANGUAGE
 #include <zephyr/types.h>
 #include <irq.h>
 #include <sw_isr_table.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
 
 /**
  * Configure a static interrupt.
@@ -210,10 +209,10 @@ static ALWAYS_INLINE void arch_nop(void)
 	__asm__ volatile("nop");
 }
 
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
-#endif
+#endif /* _ASMLANGUAGE */
+
+#endif /* ZEPHYR_INCLUDE_ARCH_NIOS2_ARCH_H_ */

include/arch/nios2/asm_inline_gcc.h

@@ -7,10 +7,6 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_NIOS2_ASM_INLINE_GCC_H_
 #define ZEPHYR_INCLUDE_ARCH_NIOS2_ASM_INLINE_GCC_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 /*
  * The file must not be included directly
  * Include arch/cpu.h instead
@@ -21,8 +17,4 @@ extern "C" {
 #include <toolchain.h>
 #endif /* _ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* _ASM_INLINE_GCC_PUBLIC_GCC_H */