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Date:   Mon, 1 Jun 2020 10:23:29 +0100
From:   Dave Martin <Dave.Martin@arm.com>
To:     Keno Fischer <keno@juliacomputing.com>
Cc:     Kyle Huey <khuey@pernos.co>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Will Deacon <will@kernel.org>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: arm64: Register modification during syscall entry/exit stop
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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.

Cheers
---Dave