linux-kernel - Re: [PATCH v2 6/7] ptrace: introduce PTRACE_SET_SYSCALL

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Message-ID: <20250115173642.GA25129@strace.io>
Date: Wed, 15 Jan 2025 19:36:42 +0200
From: "Dmitry V. Levin" <ldv@...ace.io>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Alexey Gladkov <legion@...nel.org>,
	Eugene Syromyatnikov <evgsyr@...il.com>,
	Mike Frysinger <vapier@...too.org>,
	Renzo Davoli <renzo@...unibo.it>,
	Davide Berardi <berardi.dav@...il.com>,
	strace-devel@...ts.strace.io, linux-kernel@...r.kernel.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH v2 6/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO request

On Wed, Jan 15, 2025 at 05:38:09PM +0100, Oleg Nesterov wrote:
[...]
> > +	syscall_set_nr(child, regs, nr);
> > +	/*
> > +	 * If the syscall number is set to -1, setting syscall arguments is not
> > +	 * just pointless, it would also clobber the syscall return value on
> > +	 * those architectures that share the same register both for the first
> > +	 * argument of syscall and its return value.
> > +	 */
> > +	if (nr != -1)
> > +		syscall_set_arguments(child, regs, args);
> 
> Thanks, much better than I tried to suggest in my reply to V1.
> 
> But may be
> 
> 	if (syscall_get_nr() != -1)
> 		syscall_set_arguments(...);
> 
> will look a bit more consistent?

I'm sorry, but I didn't follow.  As we've just set the syscall number with
syscall_set_nr(), why would we want to call syscall_get_nr() right after
that to obtain the syscall number?


-- 
ldv