On 14/02/17 14:46, Waiman Long wrote: > On 02/14/2017 04:39 AM, Peter Zijlstra wrote: >> On Mon, Feb 13, 2017 at 05:34:01PM -0500, Waiman Long wrote: >>> It is the address of &steal_time that will exceed the 32-bit limit. >> That seems extremely unlikely. That would mean we have more than 4G >> worth of per-cpu variables declared in the kernel. > I have some doubt about if the compiler is able to properly use > RIP-relative addressing for this. Anyway, it seems like constraints > aren't allowed for asm() when not in the function context, at least for > the the compiler that I am using (4.8.5). So it is a moot point. You can work the issue of not having parameters in a plain asm() statement by using an asm-offset, stringizing it, and have C put the string fragments back together. "cmpb $0, " STR(STEAL_TIME_preempted) "(%rax);" ~Andrew
