[PATCH v16 02/18] syscall_user_dispatch: Introduce a weak fallback for arch_syscall_is_vdso_sigreturn()

[Jinjie Ruan]

Currently, multiple architectures (LoongArch, RISC-V, S390, Powerpc)
provide identical stubs for arch_syscall_is_vdso_sigreturn() that simply
return false. This results in redundant boilerplate code across the tree.

Introduce a default __weak implementation of
arch_syscall_is_vdso_sigreturn() directly in syscall_user_dispatch.c that
returns false. This allows architectures that do not utilize a vDSO
sigreturn to entirely drop their redundant inline definitions.

Architectures requiring a specialized check (such as x86) will continue to
override this fallback with their strong symbol definitions.

Clean up the redundant implementations in loongarch, riscv, s390
and powerpc.

Cc: Thomas Gleixner <tglx@xxxxxxxxxx>
Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
 arch/loongarch/include/asm/syscall.h  | 5 -----
 arch/powerpc/include/asm/syscall.h    | 5 -----
 arch/riscv/include/asm/syscall.h      | 5 -----
 arch/s390/include/asm/syscall.h       | 5 -----
 include/linux/syscall_user_dispatch.h | 1 +
 kernel/entry/syscall_user_dispatch.c  | 5 +++++
 6 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
index df8ea223c77b..946886794ced 100644
--- a/arch/loongarch/include/asm/syscall.h
+++ b/arch/loongarch/include/asm/syscall.h
@@ -85,9 +85,4 @@ static inline int syscall_get_arch(struct task_struct *task)
 #endif
 }
 
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
-
 #endif	/* __ASM_LOONGARCH_SYSCALL_H */
diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index 834fcc4f7b54..4b3c52ed6e9d 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -139,9 +139,4 @@ static inline int syscall_get_arch(struct task_struct *task)
 	else
 		return AUDIT_ARCH_PPC64;
 }
-
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
 #endif	/* _ASM_SYSCALL_H */
diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 8067e666a4ca..987c9a78806f 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -112,11 +112,6 @@ static inline void syscall_handler(struct pt_regs *regs, ulong syscall)
 	regs->a0 = fn(regs);
 }
 
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
-
 asmlinkage long sys_riscv_flush_icache(uintptr_t, uintptr_t, uintptr_t);
 
 asmlinkage long sys_riscv_hwprobe(struct riscv_hwprobe *, size_t, size_t,
diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
index 4271e4169f45..5f310caad1fc 100644
--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h
@@ -89,11 +89,6 @@ static inline int syscall_get_arch(struct task_struct *task)
 	return AUDIT_ARCH_S390X;
 }
 
-static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
-{
-	return false;
-}
-
 #define SYSCALL_FMT_0
 #define SYSCALL_FMT_1 , "0" (r2)
 #define SYSCALL_FMT_2 , "d" (r3) SYSCALL_FMT_1
diff --git a/include/linux/syscall_user_dispatch.h b/include/linux/syscall_user_dispatch.h
index 3858a6ffdd5c..73d69e02807d 100644
--- a/include/linux/syscall_user_dispatch.h
+++ b/include/linux/syscall_user_dispatch.h
@@ -10,6 +10,7 @@
 
 #ifdef CONFIG_GENERIC_ENTRY
 
+bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs);
 int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
 			      unsigned long len, char __user *selector);
 
diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c
index d89dffcc2d64..acf545774d37 100644
--- a/kernel/entry/syscall_user_dispatch.c
+++ b/kernel/entry/syscall_user_dispatch.c
@@ -32,6 +32,11 @@ static void trigger_sigsys(struct pt_regs *regs)
 	force_sig_info(&info);
 }
 
+bool __weak arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
+{
+	return false;
+}
+
 bool syscall_user_dispatch(struct pt_regs *regs)
 {
 	struct syscall_user_dispatch *sd = &current->syscall_dispatch;
-- 
2.34.1