[PATCH] syscall_user_dispatch: Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

[Jinjie Ruan]

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

Yes, this is missing here.
> 
>>  	depends on GENERIC_ENTRY
>>  	default y
>>  	help
> 
> (...)