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From: "Russ Cox" <rsc@plan9.bell-labs.com>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] how to avoid a memset() optimization
Date: Thu, 14 Nov 2002 01:53:04 -0500	[thread overview]
Message-ID: <51251da60e579ed6058e741fa0dbff7b@plan9.bell-labs.com> (raw)

>   He doesn't need to know about volatile -- that's the whole point.
>   Once "experienced" programmer has set the buffer that way, the
>   less experienced just gets less chance to screw himself up

I'd still rather see it closer to the use that needs it.
If you're used to seeing secmemset then seeing
memset is a big red flag.  If you're used to seeing
memset with a volatile declaration, then you have
to seek out the volatile declaration, which might not
be anywhere near the call to memset.

This is a stupid argument anyway.  Volatile is a crock.
Here's another problem.  Suppose I'm worried that
leaking the processor flags at the end of my computation
might reveal something about the secret key.  I want to
clear them.  I could do something like:

	x = 0 & 0;

which in this particular case will clear the appropriate
flags.  But now the compiler comes along and optimizes
away the whole expression.  Where do I put my volatile
to make that stay?  Hmm?  The answer is not more crappy
qualifiers.  The answer is clearly dumber compilers.

Russ



             reply	other threads:[~2002-11-14  6:53 UTC|newest]

Thread overview: 104+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-11-14  6:53 Russ Cox [this message]
2002-11-14 10:22 ` Douglas A. Gwyn
2002-11-14 13:20   ` Sam
2002-11-14 15:20     ` Scott Schwartz
2002-11-14 15:26       ` Boyd Roberts
2002-11-14 15:34         ` plan9
2002-11-14 15:59           ` Sam
2002-11-14 18:57         ` Steve Kilbane
2002-11-15 10:51           ` Douglas A. Gwyn
2002-11-14 15:50       ` Dan Cross
2002-11-14 17:21         ` Douglas A. Gwyn
2002-11-14 18:51           ` Dan Cross
2002-11-14 15:50     ` Douglas A. Gwyn
2002-11-19  7:20 ` Roman V. Shaposhnick
     [not found] <sah@softcardsystems.com>
2003-02-15 14:30 ` [9fans] presentation preparation Sam
2003-02-15 19:37   ` Scott Schwartz
2003-02-15 19:48     ` andrey mirtchovski
2003-02-27  9:35       ` Ralph Corderoy
2003-02-28 18:44         ` [9fans] union directories Jack Johnson
2003-02-28 18:53           ` Russ Cox
2003-03-04  9:44           ` Adrian Tritschler
2003-02-15 20:49   ` [9fans] presentation preparation Richard Miller
2003-02-17 15:00   ` Russ Cox
2003-02-17 16:25     ` Fco.J.Ballesteros
  -- strict thread matches above, loose matches on Subject: below --
2003-01-06 10:47 [9fans] how to avoid a memset() optimization nigel
2003-01-06 11:15 ` Geoff Collyer
2002-11-19 14:32 presotto
2002-11-20  7:24 ` Tomas
2002-11-20 16:38   ` Douglas A. Gwyn
2002-11-19  8:21 Fco.J.Ballesteros
2002-11-18 21:36 Joel Salomon
2002-11-18 20:42 Andrew Simmons
2002-11-18 14:19 C H Forsyth
2002-11-15  1:56 Dennis Ritchie
2002-11-15 10:51 ` Douglas A. Gwyn
2002-11-15 12:03 ` Boyd Roberts
2002-11-14 18:55 jmk
2002-11-14 22:23 ` Steve Kilbane
2002-11-14 18:17 presotto
2002-11-14 18:11 Joel Salomon
2002-11-14 18:26 ` William Josephson
2002-11-14 17:44 rog
2002-11-15 10:50 ` Douglas A. Gwyn
2002-11-14 17:28 Russ Cox
2002-11-14 16:47 presotto
2002-11-15 10:50 ` Douglas A. Gwyn
2002-11-15 16:51   ` William Josephson
2002-11-18 10:38     ` Douglas A. Gwyn
2002-11-18 12:34       ` Ronald G. Minnich
2002-11-19  7:38 ` Roman V. Shaposhnick
2002-11-20  9:47   ` Douglas A. Gwyn
2002-11-21 20:55     ` Roman V. Shaposhnick
2002-11-22  9:59       ` Douglas A. Gwyn
2003-01-06 10:18   ` Ralph Corderoy
2003-01-06 15:42     ` Sam
2003-01-06 15:49       ` Russ Cox
2003-01-06 15:58         ` David Presotto
2003-01-06 16:02         ` Sam
     [not found] <nemo@plan9.escet.urjc.es>
2002-11-14 15:38 ` Fco.J.Ballesteros
2002-11-14 16:24   ` Scott Schwartz
2002-11-14  2:48 Dennis Ritchie
2002-11-14  4:23 ` Ronald G. Minnich
2002-11-13 18:58 Rob `Commander' Pike
2002-11-13 14:40 C H Forsyth
2002-11-13 15:54 ` rob pike
2002-11-13 16:05   ` andrey mirtchovski
2002-11-13 16:32   ` Ronald G. Minnich
2002-11-14 10:21     ` Douglas A. Gwyn
2002-11-14 17:07       ` Ronald G. Minnich
2002-11-22  9:59     ` Clint Olsen
2002-11-13 16:56   ` William K. Josephson
2002-11-14 10:21     ` Douglas A. Gwyn
2002-11-14 16:48       ` William Josephson
2002-11-14 10:21   ` Douglas A. Gwyn
2002-11-14 14:46     ` Dan Cross
2002-11-14 16:59       ` Douglas A. Gwyn
2002-11-14 18:31         ` Tad Hunt
2002-11-15 10:50           ` Douglas A. Gwyn
2002-11-18 14:27         ` Aharon Robbins
2002-11-13 14:14 Skip Tavakkolian
2002-11-13 13:55 rog
2002-11-13 13:38 Skip Tavakkolian
2002-11-13 16:25 ` Boyd Roberts
2002-11-13 10:43 C H Forsyth
2002-11-14 10:21 ` Douglas A. Gwyn
2002-11-13  6:52 Geoff Collyer
2002-11-13 10:13 ` Boyd Roberts
2002-11-13  6:34 Andrew Simmons
2002-11-13  6:43 ` Doc Shipley
2002-11-13  1:47 Russ Cox
2002-11-13 10:16 ` Douglas A. Gwyn
2002-11-14  1:46 ` Roman V. Shaposhnick
2002-11-14  1:52   ` William Josephson
2002-11-14  6:42     ` Roman V. Shaposhnick
2002-11-13  0:31 Russ Cox
2002-11-13  1:26 ` Roman V. Shaposhnick
2002-11-13 10:15   ` Douglas A. Gwyn
2002-11-14  1:42     ` Roman V. Shaposhnick
2002-11-13 10:15 ` Douglas A. Gwyn
2002-11-13  0:20 presotto
2002-11-12 22:42 Roman V. Shaposhnick
2002-07-16 15:53 [9fans] useful language extension, or no? rob pike, esq.
2002-07-16 15:05 ` Sam
2002-07-16 21:29   ` Steve Kilbane

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