[PATCH] syscall_user_dispatch: Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

[PATCH] syscall_user_dispatch: Introduce ARCH_SUPPORTS_SYSCALL_USER_DISPATCH

[Jinjie Ruan]

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.

Link: https://lore.kernel.org/linux-arm-kernel/akZgV0Y4YAmB43_g@J2N7QTR9R3.cambridge.arm.com/
Cc: Thomas Gleixner <tglx@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Suggested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Jinjie Ruan <ruanjinjie@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
 	depends on GENERIC_ENTRY
 	default y
 	help
diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
index df8ea223c77b..d9275010f548 100644
--- a/arch/loongarch/include/asm/syscall.h
+++ b/arch/loongarch/include/asm/syscall.h
@@ -84,10 +84,4 @@ static inline int syscall_get_arch(struct task_struct *task)
 	return AUDIT_ARCH_LOONGARCH64;
 #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/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..f3f8ad107eeb 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -335,6 +335,7 @@ config X86
 	select SCHED_SMT			if SMP
 	select ARCH_SUPPORTS_SCHED_CLUSTER	if SMP
 	select ARCH_SUPPORTS_SCHED_MC		if SMP
+	select ARCH_SUPPORTS_SYSCALL_USER_DISPATCH
 	select HAVE_SINGLE_FTRACE_DIRECT_OPS	if X86_64 && DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 
 config INSTRUCTION_DECODER
-- 
2.34.1

Re: [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@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Ada Couprie Diaz <ada.coupriediaz@arm.com>
> Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Jinjie Ruan <ruanjinjie@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

(...)

Re: [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@kernel.org>
>> Cc: Mark Rutland <mark.rutland@arm.com>
>> Cc: Ada Couprie Diaz <ada.coupriediaz@arm.com>
>> Cc: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
>> Suggested-by: Mark Rutland <mark.rutland@arm.com>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@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
> 
> (...)