On 7/9/2026 3:36 PM, Thomas Weißschuh wrote:

On Thu, Jul 09, 2026 at 03:28:03PM +0800, Jinjie Ruan wrote:

quoted

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.

quoted

Link: https://lore.kernel.org/linux-arm-kernel/akZgV0Y4YAmB43_g@J2N7QTR9R3.cambridge.arm.com/ (local)
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ada Couprie Diaz <redacted>
Cc: Thomas Weißschuh <redacted>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jinjie Ruan <redacted>
---
 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

Yes, this is missing here.

quoted

 	depends on GENERIC_ENTRY
 	default y
 	help

(...)