[PATCH v2 07/10] x86: fix duplicate extern declarations
From: Safocl Stollmannovic
Date: Fri Nov 13 2026 - 02:37:48 EST
Compiling a kernel module with a C++ compiler results in a "duplicate
extern specifier" error.
This occurs because the code contains `extern asmlinkage`, and `asmlinkage`
expands to `extern C` when processed by a C++ compiler.
Since the code already contains sections that respond to a C++ compiler,
I believe it is a perfectly valid approach to gradually move toward a state
where kernel modules can be compiled by a C++ compiler without any issues.
The `extern` specifier must be removed.
Link: https://bugzilla.kernel.org/show_bug.cgi?id=222257
Signed-off-by: Safocl Stollmannovic <safocl88@xxxxxxxxx>
---
arch/x86/include/asm/efi.h | 2 +-
arch/x86/include/asm/gsseg.h | 2 +-
arch/x86/include/asm/preempt.h | 8 ++++----
arch/x86/include/asm/processor.h | 2 +-
arch/x86/include/asm/suspend.h | 2 +-
arch/x86/um/sys_call_table_32.c | 4 ++--
arch/x86/um/sys_call_table_64.c | 4 ++--
7 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index be58b7f5c..f5cb179b8 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -94,7 +94,7 @@ static inline void efi_fpu_end(void)
#else /* !CONFIG_X86_32 */
#define EFI_X86_KERNEL_ALLOC_LIMIT EFI_ALLOC_LIMIT
-extern asmlinkage u64 __efi_call(void *fp, ...);
+asmlinkage u64 __efi_call(void *fp, ...);
extern bool efi_disable_ibt_for_runtime;
diff --git a/arch/x86/include/asm/gsseg.h b/arch/x86/include/asm/gsseg.h
index ab6a595ce..81ef16081 100644
--- a/arch/x86/include/asm/gsseg.h
+++ b/arch/x86/include/asm/gsseg.h
@@ -12,7 +12,7 @@
#ifdef CONFIG_X86_64
-extern asmlinkage void asm_load_gs_index(u16 selector);
+asmlinkage void asm_load_gs_index(u16 selector);
/* Replace with "lkgs %di" once binutils support LKGS instruction */
#define LKGS_DI _ASM_BYTES(0xf2,0x0f,0x00,0xf7)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index d16d9c2f7..135695ae3 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -134,11 +134,11 @@ static __always_inline bool should_resched(int preempt_offset)
#ifdef CONFIG_PREEMPTION
-extern asmlinkage void preempt_schedule(void);
-extern asmlinkage void preempt_schedule_thunk(void);
+asmlinkage void preempt_schedule(void);
+asmlinkage void preempt_schedule_thunk(void);
-extern asmlinkage void preempt_schedule_notrace(void);
-extern asmlinkage void preempt_schedule_notrace_thunk(void);
+asmlinkage void preempt_schedule_notrace(void);
+asmlinkage void preempt_schedule_notrace_thunk(void);
#define __preempt_schedule() \
asm volatile ("call preempt_schedule_thunk" : ASM_CALL_CONSTRAINT);
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 77488ff5e..68d7292af 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -455,7 +455,7 @@ static inline unsigned long cpu_kernelmode_gs_base(int cpu)
#endif
}
-extern asmlinkage void entry_SYSCALL32_ignore(void);
+asmlinkage void entry_SYSCALL32_ignore(void);
/* Save actual FS/GS selectors and bases to current->thread */
void current_save_fsgs(void);
diff --git a/arch/x86/include/asm/suspend.h b/arch/x86/include/asm/suspend.h
index a892494ca..e29c071b9 100644
--- a/arch/x86/include/asm/suspend.h
+++ b/arch/x86/include/asm/suspend.h
@@ -11,4 +11,4 @@ extern unsigned long temp_pgt __visible;
extern unsigned long relocated_restore_code __visible;
extern int relocate_restore_code(void);
/* Defined in hibernate_asm_32/64.S */
-extern asmlinkage __visible int restore_image(void);
+asmlinkage __visible int restore_image(void);
diff --git a/arch/x86/um/sys_call_table_32.c b/arch/x86/um/sys_call_table_32.c
index 51655133e..f79c0138e 100644
--- a/arch/x86/um/sys_call_table_32.c
+++ b/arch/x86/um/sys_call_table_32.c
@@ -9,7 +9,7 @@
#include <linux/cache.h>
#include <asm/syscall.h>
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
+asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
unsigned long, unsigned long,
unsigned long, unsigned long);
@@ -28,7 +28,7 @@ extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
#define __SYSCALL_WITH_COMPAT(nr, native, compat) __SYSCALL(nr, native)
#define __SYSCALL_NORETURN __SYSCALL
-#define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
+#define __SYSCALL(nr, sym) asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
#include <asm/syscalls_32.h>
#undef __SYSCALL
diff --git a/arch/x86/um/sys_call_table_64.c b/arch/x86/um/sys_call_table_64.c
index 943d414f2..555e65e66 100644
--- a/arch/x86/um/sys_call_table_64.c
+++ b/arch/x86/um/sys_call_table_64.c
@@ -9,7 +9,7 @@
#include <linux/cache.h>
#include <asm/syscall.h>
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
+asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
unsigned long, unsigned long,
unsigned long, unsigned long);
@@ -24,7 +24,7 @@ extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
#define __SYSCALL_NORETURN __SYSCALL
-#define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
+#define __SYSCALL(nr, sym) asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
#include <asm/syscalls_64.h>
#undef __SYSCALL
--
2.56.1