[PATCH] syscall_user_dispatch: Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

[Thomas Weißschuh]

On Thu, Jul 09, 2026 at 03:28:03PM +0800, Jinjie Ruan wrote:
> Currently, only x86 genuinely implements and supports Syscall User
> Dispatch (SUD). Multiple architectures provide a stub
> arch_syscall_is_vdso_sigreturn() returning 'false' simply to satisfy
> GENERIC_ENTRY compilation, which creates a false impression of feature
> support.
> 
> Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH to decouple this mechanism
> from GENERIC_ENTRY. Select it exclusively on x86 and remove the redundant
> stub functions from other architectures.

Nice, this confused me before.

> Link: https://lore.kernel.org/linux-arm-kernel/akZgV0Y4YAmB43_g@J2N7QTR9R3.cambridge.arm.com/
> Cc: Thomas Gleixner <tglx at kernel.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Ada Couprie Diaz <ada.coupriediaz at arm.com>
> Cc: Thomas Weißschuh <thomas.weissschuh at linutronix.de>
> Suggested-by: Mark Rutland <mark.rutland at arm.com>
> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
> ---
>  arch/Kconfig                         | 1 +
>  arch/loongarch/include/asm/syscall.h | 6 ------
>  arch/powerpc/include/asm/syscall.h   | 5 -----
>  arch/riscv/include/asm/syscall.h     | 5 -----
>  arch/s390/include/asm/syscall.h      | 5 -----
>  arch/x86/Kconfig                     | 1 +
>  6 files changed, 2 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 0c01521c2f3f..393d0fb75eac 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -116,6 +116,7 @@ config GENERIC_ENTRY
>  
>  config SYSCALL_USER_DISPATCH
>  	bool "Syscall User Dispatch"
> +	depends on ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

ARCH_SUPPORTS_SYSCALL_USER_DISPATCH is not declared as a config option,
so the 'select' will not do anything. Needs this:

config ARCH_SUPPORTS_SYSCALL_USER_DISPATCH
	bool

>  	depends on GENERIC_ENTRY
>  	default y
>  	help

(...)