On Wed, Feb 29, 2012 at 02:44:24PM +0000, Ian Campbell wrote: > > If you need a specific register, this means that you must set up that > > register explicitly inside the asm if you want a guarantee that the > > code will work: > > > > asm volatile ( > > "movw r12, %[hvc_num]\n\t" > > Is gcc (or gas?) smart enough to optimise this away if it turns out that > %[hvc_num] == r12? No, and it won't do, because %[hvc_num] is specified in these operands: > > ... > > "hvc #0" > > :: [hvc_num] "i" (NUMBER) : "r12" to be an integer, not a register. > How are system calls implemented on the userspace side? I confess I > don't know what the ARM syscall ABI looks like -- is it all registers or > is some of it on the stack? It sounds like the solution ought to be > pretty similar though. All registers. We have a few which take a pointer to an in memory array, but those are for some old multiplexed syscalls. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
