arc: 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.

In arch/arc/arch.h the extern "C" in the including context is left
active during an include to avoid more complex restructuring.

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 <peter.bigot@nordicsemi.no>

arch/arc/include/kernel_arch_data.h

@@ -20,10 +20,6 @@
 #ifndef ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_DATA_H_
 #define ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_DATA_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <toolchain.h>
 #include <linker/sections.h>
 #include <arch/cpu.h>
@@ -36,9 +32,11 @@ extern "C" {
 #include <zephyr/types.h>
 #include <sys/util.h>
 #include <sys/dlist.h>
+
+#ifdef __cplusplus
+extern "C" {
 #endif
 
-#ifndef _ASMLANGUAGE
 #ifdef CONFIG_ARC_HAS_SECURE
 struct _irq_stack_frame {
 	u32_t lp_end;
@@ -170,6 +168,10 @@ struct _callee_saved_stack {
 
 typedef struct _callee_saved_stack _callee_saved_stack_t;
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _ASMLANGUAGE */
 
 /* stacks */
@@ -179,8 +181,5 @@ typedef struct _callee_saved_stack _callee_saved_stack_t;
 #define STACK_ROUND_UP(x) ROUND_UP(x, STACK_ALIGN_SIZE)
 #define STACK_ROUND_DOWN(x) ROUND_DOWN(x, STACK_ALIGN_SIZE)
 
-#ifdef __cplusplus
-}
-#endif
 
 #endif /* ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_DATA_H_ */

arch/arc/include/kernel_arch_func.h

@@ -20,10 +20,6 @@
 #ifndef ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_FUNC_H_
 #define ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_FUNC_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #if !defined(_ASMLANGUAGE)
 
 #ifdef CONFIG_CPU_ARCV2
@@ -31,6 +27,10 @@ extern "C" {
 #include <v2/irq.h>
 #endif
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 static ALWAYS_INLINE _cpu_t *z_arch_curr_cpu(void)
 {
 #ifdef CONFIG_SMP
@@ -80,10 +80,10 @@ extern void z_arc_fatal_error(unsigned int reason, const z_arch_esf_t *esf);
 
 extern void z_arch_sched_ipi(void);
 
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_FUNC_H_ */

arch/arc/include/kernel_arch_thread.h

@@ -31,6 +31,10 @@
 #ifndef _ASMLANGUAGE
 #include <zephyr/types.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 struct _callee_saved {
 	u32_t sp; /* r28 */
 };
@@ -60,6 +64,11 @@ struct _thread_arch {
 
 typedef struct _thread_arch _thread_arch_t;
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* _ASMLANGUAGE */
 
+
 #endif /* ZEPHYR_ARCH_ARC_INCLUDE_KERNEL_ARCH_THREAD_H_ */

arch/arc/include/swap_macros.h

@@ -14,10 +14,6 @@
 #include <toolchain.h>
 #include <arch/cpu.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifdef _ASMLANGUAGE
 
 /* entering this macro, current is in r2 */
@@ -338,8 +334,4 @@ extern "C" {
 
 #endif /* _ASMLANGUAGE */
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /*  ZEPHYR_ARCH_ARC_INCLUDE_SWAP_MACROS_H_ */

arch/arc/include/v2/cache.h

@@ -17,12 +17,12 @@
 
 #include <arch/cpu.h>
 
+#ifndef _ASMLANGUAGE
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#ifndef _ASMLANGUAGE
-
 /* i-cache defines for IC_CTRL register */
 #define IC_CACHE_ENABLE   0x00
 #define IC_CACHE_DISABLE  0x01
@@ -50,10 +50,10 @@ static ALWAYS_INLINE void z_icache_setup(void)
 	}
 }
 
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_ARCH_ARC_INCLUDE_V2_CACHE_H_ */

arch/arc/include/vector_table.h

@@ -21,10 +21,6 @@
 #ifndef ZEPHYR_ARCH_ARC_INCLUDE_VECTOR_TABLE_H_
 #define ZEPHYR_ARCH_ARC_INCLUDE_VECTOR_TABLE_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #define EXC_EV_TRAP	0x9
 
 #ifdef _ASMLANGUAGE
@@ -55,6 +51,10 @@ GTEXT(_isr_wrapper)
 
 #else
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern void __reset(void);
 extern void __memory_error(void);
 extern void __instruction_error(void);
@@ -70,10 +70,10 @@ extern void __ev_div_zero(void);
 extern void __ev_dc_error(void);
 extern void __ev_maligned(void);
 
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_ARCH_ARC_INCLUDE_VECTOR_TABLE_H_ */

include/arch/arc/arch.h

@@ -160,6 +160,8 @@ extern "C" {
 
 #ifdef CONFIG_ARC_MPU
 #ifndef _ASMLANGUAGE
+
+/* Legacy case: retain containing extern "C" with C++ */
 #include <arch/arc/v2/mpu/arc_mpu.h>
 
 #define K_MEM_PARTITION_P_NA_U_NA	AUX_MPU_ATTR_N

include/arch/arc/v2/arc_connect.h

@@ -14,14 +14,13 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_ARC_V2_ARC_CONNECT_H_
 #define ZEPHYR_INCLUDE_ARCH_ARC_V2_ARC_CONNECT_H_
 
+#ifndef _ASMLANGUAGE
+#include <zephyr/types.h>
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#ifndef _ASMLANGUAGE
-#include <zephyr/types.h>
-
 #define _ARC_V2_CONNECT_BCR 0x0d0
 #define _ARC_V2_CONNECT_IDU_BCR 0x0d5
 #define _ARC_V2_CONNECT_GFRC_BCR 0x0d6
@@ -227,9 +226,10 @@ extern void z_arc_connect_idu_set_mask(u32_t irq_num, u32_t mask);
 extern u32_t z_arc_connect_idu_read_mask(u32_t irq_num);
 extern u32_t z_arc_connect_idu_check_first(u32_t irq_num);
 
-#endif
-
 #ifdef __cplusplus
 }
 #endif
+
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_INCLUDE_ARCH_ARC_V2_ARC_CONNECT_H_ */

include/arch/arc/v2/asm_inline_gcc.h

@@ -9,26 +9,25 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_ARC_V2_ASM_INLINE_GCC_H_
 #define ZEPHYR_INCLUDE_ARCH_ARC_V2_ASM_INLINE_GCC_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <zephyr/types.h>
 #include <stddef.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
 /**
  *  @brief read timestamp register (CPU frequency)
  */
 extern u64_t z_tsc_read(void);
 
-
-
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_INCLUDE_ARCH_ARC_V2_ASM_INLINE_GCC_H_ */

include/arch/arc/v2/aux_regs.h

@@ -15,10 +15,6 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_ARC_V2_AUX_REGS_H_
 #define ZEPHYR_INCLUDE_ARCH_ARC_V2_AUX_REGS_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #define _ARC_V2_LP_START 0x002
 #define _ARC_V2_LP_END 0x003
 #define _ARC_V2_IDENTITY 0x004
@@ -201,8 +197,4 @@ extern "C" {
 		__ret;                                   \
 	})
 
-#ifdef __cplusplus
-}
-#endif
-
 #endif /* ZEPHYR_INCLUDE_ARCH_ARC_V2_AUX_REGS_H_ */

include/arch/arc/v2/ffs.h

@@ -14,14 +14,14 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_ARC_V2_FFS_H_
 #define ZEPHYR_INCLUDE_ARCH_ARC_V2_FFS_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <zephyr/types.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /**
  *
  * @brief find most significant bit set in a 32-bit word
@@ -81,10 +81,10 @@ static ALWAYS_INLINE unsigned int find_lsb_set(u32_t op)
 }
 #endif
 
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_INCLUDE_ARCH_ARC_V2_FFS_H_ */

include/arch/arc/v2/sys_io.h

@@ -7,10 +7,6 @@
 #ifndef ZEPHYR_INCLUDE_ARCH_ARC_V2_SYS_IO_H_
 #define ZEPHYR_INCLUDE_ARCH_ARC_V2_SYS_IO_H_
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #ifndef _ASMLANGUAGE
 
 #include <sys/sys_io.h>
@@ -18,6 +14,11 @@ extern "C" {
 
 #include <zephyr/types.h>
 #include <stddef.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* Implementation of sys_io.h's documented functions */
 
 static ALWAYS_INLINE
@@ -300,10 +301,10 @@ static ALWAYS_INLINE
 	return ret;
 }
 
-#endif /* _ASMLANGUAGE */
-
 #ifdef __cplusplus
 }
 #endif
 
+#endif /* _ASMLANGUAGE */
+
 #endif /* ZEPHYR_INCLUDE_ARCH_ARC_V2_SYS_IO_H_ */

soc/arc/snps_arc_iot/sysconf.h

@@ -8,12 +8,12 @@
 #ifndef _ARC_IOT_SYSCONF_H_
 #define _ARC_IOT_SYSCONF_H_
 
+#include <stdint.h>
+
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-#include <stdint.h>
-
 typedef struct sysconf_reg {
 	volatile uint32_t reserved1;	/* 0x0 */
 	volatile uint32_t AHBCLKDIV;	/* AHB clock divisor */
@@ -164,4 +164,4 @@ extern void arc_iot_eflash_clk_div(uint8_t div);
 }
 #endif
 
-#endif /* _ARC_IOT_SYSCONF_H_ */
+#endif /* _ARC_IOT_SYSCONF_H_ */