Re: [RFC] ptrace: add generic SET_SYSCALL request

[Russell King - ARM Linux]

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.

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