Re: Is clobber "memory" in include/asm-i386/system.h necessary?

Simon Shapiro (
Wed, 15 May 1996 08:41:24 -0700 (PDT)

Hi Linus Torvalds; On 07-May-96 you wrote:


> "volatile" is _never_ a good idea, even in SMP. You already touched on
> why it's not a good idea: it's unnecessary if we have some locking to
> prevent concurrent accesses.

Except for emmory mapped I/O.


int *x; /* Some memory mapped I/O port */


*x = 1; //* Initialize */

while ( *x )

What will the compiler/optimizer do with this?
The purpose of volatile was to protect such cases, if my memory serves me.

> Now, if we DON'T have locking that prevents concurrent accesses, then we
> have a major bug in the system.

Locks are locks. Not having locks is bad.

> Ergo, using "volatile" means that we have a major bug in the system.

Using volatile as a lock is bad. True enough. But not necessarily bad in
itself. Unless GCC is broken, that is (always a possibility :-).

Sincerely Yours, (Sent on 05/15/96, 08:41:24 by XF-Mail)

Simon Shapiro i-Connect.Net, a Division of iConnect Corp.
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