Re: [PATCH] mark read_crX() asm code as volatile

From: H. Peter Anvin
Date: Wed Oct 03 2007 - 02:22:11 EST


Nick Piggin wrote:

This should work because the result gets used before reading again:

read_cr3(a);
write_cr3(a | 1);
read_cr3(a);

But this might be reordered so that b gets read before the write:

read_cr3(a);
write_cr3(a | 1);
read_cr3(b);

?

I don't see how, as write_cr3 clobbers memory.

Because read_cr3() doesn't depend on memory, and b could be stored in a register.

-hpa
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