Re: [RFC] ptrace: add generic SET_SYSCALL request

On Fri, Nov 07, 2014 at 01:03:00PM +0100, Arnd Bergmann wrote:

On Friday 07 November 2014 11:55:51 Will Deacon wrote:

...

We need this for arm64 and, since all architectures seem to have a mechanism for setting a system call via ptrace, moving it to generic code should make sense for new architectures too, no?

It makes a little more sense now, but I still don't understand why you need to set the system call number via ptrace. What is this used for, and why doesn't any other architecture have this?

All other architectures have a way. x86, for example, you set orig_eax (or orig_rax) to change the syscall number. On ARM, that doesn't work because we don't always pass the syscall number in a register.