From: "H. Peter Anvin" <hpa@zytor.com>
To: Roland McGrath <roland@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@elte.hu>,
Christoph Hellwig <hch@infradead.org>,
Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>,
Vitaly Mayatskikh <v.mayatskih@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: Q: put_user_try & co (Was: [PATCH 1/5] Split wait_noreap_copyout())
Date: Wed, 20 May 2009 13:56:24 -0700 [thread overview]
Message-ID: <4A146E78.6000600@zytor.com> (raw)
In-Reply-To: <20090520201127.48B54FC38D@magilla.sf.frob.com>
Roland McGrath wrote:
>
> You mean &&__efault_label here (it's a funny syntax, but that's how it is).
> &&label is a GCC extension that I'm not sure the kernel has used before.
>
> I think it can be touchy to have an asm jump into compiled code that way.
> e.g., perhaps the compiler produced:
>
> mov reg, 40(sp)
> mov $123, reg
> #APP
> ... inside of your asm ...
> #NO_APP
> mov 40(sp), reg
>
> or some such thing. If you jump away from inside the asm, you won't ever
> do "mov 40(sp), reg". But the compiler might think that reg has its
> original value at the __efault_label: code location.
>
> Perhaps more important than any particular compiler-confusion scenario we
> can come up with is simply that this would be an obscure corner of code
> generation in the compiler that the kernel has not evoked before. There
> might be bugs or oddities in various compilers of various vintages, that
> we don't know about because they never came up before.
>
Yes, it seems like a bad idea to me.
-hpa
next prev parent reply other threads:[~2009-05-20 21:01 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-11 10:12 [PATCH 0/5] wait_task_* cleanups Vitaly Mayatskikh
2009-05-11 10:12 ` [PATCH 1/5] Split wait_noreap_copyout() Vitaly Mayatskikh
2009-05-11 10:20 ` Ingo Molnar
2009-05-11 11:20 ` Vitaly Mayatskikh
2009-05-11 12:04 ` Christoph Hellwig
2009-05-11 12:17 ` Ingo Molnar
2009-05-11 20:47 ` Vitaly Mayatskikh
2009-05-11 21:04 ` Ingo Molnar
2009-05-20 19:03 ` Q: put_user_try & co (Was: [PATCH 1/5] Split wait_noreap_copyout()) Oleg Nesterov
2009-05-20 20:11 ` Roland McGrath
2009-05-20 20:56 ` H. Peter Anvin [this message]
2009-05-21 13:42 ` Oleg Nesterov
2009-05-20 21:14 ` Andreas Schwab
2009-05-11 12:17 ` [PATCH 1/5] Split wait_noreap_copyout() Vitaly Mayatskikh
2009-05-11 10:12 ` [PATCH 2/5] Use wait_copyout() in wait_task_stopped() Vitaly Mayatskikh
2009-05-11 10:12 ` [PATCH 3/5] Use wait_copyout() in do_wait() Vitaly Mayatskikh
2009-05-11 10:12 ` [PATCH 4/5] Use wait_copyout() in wait_task_zombie() Vitaly Mayatskikh
2009-05-11 10:12 ` [PATCH 5/5] Use wait_copyout() in wait_task_continued() Vitaly Mayatskikh
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