linux-kernel - Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird crap with vdso on uml/i386)

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Message-ID: <20110822020737.GP2203@ZenIV.linux.org.uk>
Date:	Mon, 22 Aug 2011 03:07:38 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Andrew Lutomirski <luto@....edu>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, Richard Weinberger <richard@....at>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: SYSCALL, ptrace and syscall restart breakages (Re: [RFC] weird
 crap with vdso on uml/i386)

On Sun, Aug 21, 2011 at 10:01:40PM -0400, Andrew Lutomirski wrote:

>  3. We're worried that pt_regs-using compat syscalls might want the
> regs to appear to match the actual arguments (why?)

run strace and you'll see why.

>  4. ptrace expects the "registers" when SYSCALL happens to match the
> int 0x80 convention.  (This is, IMO, sick.)

That's what ptrace is *for*.  It's there to let debuggers play with
the program being debugged, including taking a look at the syscall
arguments and modifying them.  In a predictable way, please.
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