[RFC] ptrace: add generic SET_SYSCALL request

[arnd@arndb.de (Arnd Bergmann)]

On Friday 07 November 2014 16:47:23 AKASHI Takahiro wrote:
> This patch adds a new generic ptrace request, PTRACE_SET_SYSCALL.
> It can be used to change a system call number as follows:
>     ret = ptrace(pid, PTRACE_SET_SYSCALL, null, new_syscall_no);
> 'new_syscall_no' can be -1 to skip this system call, you need to modify
> a register's value, in arch-specific way, as return value though.
> 
> Please note that we can't define PTRACE_SET_SYSCALL macro in
> uapi/linux/ptrace.h partly because its value on arm, 23, is used as another
> request on sparc.
> 
> This patch also contains an example of change on arch side, arm.
> Only syscall_set_nr() is required to be defined in asm/syscall.h.
> 
> Currently only arm has this request, while arm64 would also have it
> once my patch series of seccomp for arm64 is merged. It will also be
> usable for most of other arches.
> See the discussions in lak-ml:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/300167.html
> 
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
> 

Can you describe why you are moving the implementation? Is this a feature
that we want to have on all architectures in the future? As you say,
only arm32 implements is at the moment.

	Arnd