Date: Fri, 08 Dec 2000 10:07:39 -0800 From: Julian Elischer <julian@elischer.org> To: current@freebsd.org Subject: __asm help.. Message-ID: <3A31236B.23501A47@elischer.org>
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I'm trying to write some experimental mutex operations similar to those
in -current, but to do differnt things (e.g. a read/write lock)
however, I am having some problems with the __asm stuff.
What I want to do is to define some operations that will
assemble down to:
pushfl
cli
[stuff]
popfl
I can generate the code, but it seems to me that there should be
a way of telling gcc that you have just pushed an item onto the stack,
so that if you were to have some C code between the push and po
(of the flags reg) the compiler has a correct idea of where the
SP is. I can imagine that it doesn't matter so it may be that there
is no constaint for that purpose (I read the gcc asm info pages)
but I wanted to make sure that that is the case because if it does turn
out to be important, it may manifest itself as a wierd bug sometime
in 2002.
The current pushfl code in the kernel has the following:
__asm __volatile("pushfl; popl %0" : "=r" (ef));
which has no long term effect on the stack pointer so I cannot
use it as a guide.
--
__--_|\ Julian Elischer
/ \ julian@elischer.org
( OZ ) World tour 2000
---> X_.---._/ presently in: Budapest
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