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