Re: [PATCH v2 02/16] sparc/compat: Provide an accurate in_compat_syscall implementation

[Sam Ravnborg <sam@ravnborg.org>]

On Mon, Jan 25, 2016 at 02:24:16PM -0800, Andy Lutomirski wrote:
> On sparc64 compat-enabled kernels, any task can make 32-bit and
> 64-bit syscalls.  is_compat_task returns true in 32-bit tasks, which
> does not necessarily imply that the current syscall is 32-bit.
> 
> Provide an in_compat_syscall implementation that checks whether the
> current syscall is compat.
> 
> As far as I know, sparc is the only architecture on which
> is_compat_task checks the compat status of the task and on which the
> compat status of a syscall can differ from the compat status of the
> task.  On x86, is_compat_task checks the syscall type, not the task
> type.
> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
>  arch/sparc/include/asm/compat.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/sparc/include/asm/compat.h b/arch/sparc/include/asm/compat.h
> index 830502fe62b4..5467404857fc 100644
> --- a/arch/sparc/include/asm/compat.h
> +++ b/arch/sparc/include/asm/compat.h
> @@ -307,4 +307,10 @@ static inline int is_compat_task(void)
>  	return test_thread_flag(TIF_32BIT);
>  }
>  
> +static inline bool in_compat_syscall(void)
> +{
> +	return pt_regs_trap_type(current_pt_regs()) == 0x110;
Could you please add a comment about where 0x110 comes from.
I at least failed to track this down.

	Sam