Re: arm64: Register modification during syscall entry/exit stop

From: Dave Martin
Date: Mon Jun 01 2020 - 05:23:36 EST

On Sun, May 31, 2020 at 12:20:51PM -0400, Keno Fischer wrote:
> > Can't PTRACE_SYSEMU be emulated by using PTRACE_SYSCALL, cancelling the
> > syscall at the syscall enter stop, then modifying the regs at the
> > syscall exit stop?
> Yes, it can. The idea behind SYSEMU is to be able to save half the
> ptrace traps that would require, in theory making the ptracer
> a decent amount faster. That said, the x7 issue is orthogonal to
> SYSEMU, you'd have the same issues if you used PTRACE_SYSCALL.

Right, I just wondered whether there was some deeper difference between
the two approaches.