[RFC] ptrace: add generic SET_SYSCALL request

[Will Deacon]

On Wed, Nov 12, 2014 at 10:46:01AM +0000, AKASHI Takahiro wrote:
> On 11/07/2014 11:04 PM, Oleg Nesterov wrote:
> > To me the fact that PTRACE_SET_SYSCALL can be undefined and syscall_set_nr()
> > is very much arch-dependant (but most probably trivial) means that this  code
> > should live in arch_ptrace().
> 
> Thinking of Oleg's comment above, it doesn't make sense neither to define generic
> NT_SYSTEM_CALL (user_regset) in uapi/linux/elf.h and implement it in ptrace_regset()
> in kernel/ptrace.c with arch-defined syscall_(g)set_nr().
> 
> Since we should have the same interface on arm and arm64, we'd better implement
> ptrace(PTRACE_SET_SYSCALL) locally on arm64 for now (as I originally submitted).

I think the regset approach is cleaner. We already do something similar for
TLS. That would be implemented under arch/arm64/ with it's own NT type.

Will