On Sun, Jun 19, 2016 at 11:01:48PM -0700, Andy Lutomirski wrote: > > The tmll instruction tests if any of the higher bits within the 16k > > stackframe address are set. In this specific case that would be bits 7-15 > > (mask 0x3f80). If no bit would be set we know that only up to 128 bytes > > would be left on the stack, and thus trigger an exception. > > > > This check does of course only work if a 16k stack is also 16k aligned, > > which is always the case. > > > > Oh, interesting. How do you handle the case of a single function that > uses more than 128 bytes of stack?
The compiler uses the next larger value of the stackframe size that is a power of 2 for checking. So another example with a stackframe size of 472 bytes would be the below one with a mask of 0x3e00: 0000000000392db8 <htree_inlinedir_to_tree>: 392db8: eb 6f f0 48 00 24 stmg %r6,%r15,72(%r15) 392dbe: a7 f1 3e 00 tmll %r15,15872 392dc2: b9 04 00 ef lgr %r14,%r15 392dc6: a7 84 00 01 je 392dc8 <htree_inlinedir_to_tree+0x10> 392dca: e3 f0 fe 28 ff 71 lay %r15,-472(%r15)
