Re: [PATCH] Set unknown_syscall differently on arm linux

Yao Qi
2016-06-30T07:52:16Z

On Wed, Jun 29, 2016 at 6:41 PM, Mike Frysinger <vapier@gentoo.org> wrote:
> On 28 Jun 2016 10:26, Yao Qi wrote:
>> Currently, we use 123456789 as unknown or illegal syscall number, and
>> expect program return ENOSYS. Although 123456789 is an illegal syscall
>> number on arm linux, kernel sends SIGILL rather than returns -ENOSYS.
>
> err, what ? calling random syscalls should not result in signals being
> generated (ignoring obvious ones like __NR_kill). is the kernel broken ?
> i think this needs more investigation & explanation.

I checked kernel source arch/arm/kernel/traps.c:arm_syscall, and that is how
I get the knowledge that kernel doesn't raise SIGIILL if sysno is within
0xf0001..0xf07ff. That is intentional, but I don't know why arm kernel behaves
this way.

--
Yao (齐尧)