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

[Mukesh Kumar Chaurasiya]

On Mon, Jun 29, 2026 at 09:06:00PM +0800, Jinjie Ruan wrote:
> 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 at kernel.org>
> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
> ---
>  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
> 

Build and boot tested on ppc with P11 LPAR. LGTM.

Tested-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras at gmail.com>
Reviewed-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras at gmail.com>