On Mon, Oct 31, 2016 at 5:06 PM, Richard Henderson <r...@twiddle.net> wrote: > On 10/31/2016 09:40 AM, Artyom Tarasenko wrote: >>> >>> * The "Remove asi helper code handled inline" patch retains the code >>> within >>> ldda to handle asis that must be handled out of line. This fixes the >>> FreeBSD 10.3 boot problem. While the UA2007 spec (and thus sun4v?) >>> doesn't >>> allow for such, it would seem that US2 hardware does. >> >> >> What ASI was failing? It may still be a part of sun4v CPUs if it's >> described in UST1/UST2 supplements. > > > 0x00000000c08e5680: clr %g4 > 0x00000000c08e5684: mov 1, %g1 > 0x00000000c08e5688: sllx %g1, 0x24, %o5 > 0x00000000c08e568c: mov -1, %g1 > 0x00000000c08e5690: sllx %g1, 0x23, %g1 > 0x00000000c08e5694: xor %g1, -128, %o4 > 0x00000000c08e5698: ldda [ %g4 ] #ASI_IC_TAG, %g0 **** > 0x00000000c08e569c: mov %g1, %g2 > 0x00000000c08e56a0: and %g1, %o5, %g1 > 0x00000000c08e56a4: brz,a %g1, 0xc08e56dc > > So indeed it would appear that FreeBSD does in fact want the half of the > result that would get stored into %g1. As far as I can see they could have > achieved the same result with > > ldxa [%g4] #ASI_IC_TAG, %g1 > srl %g1, 0, %g1 > > to stay within the nominal spec.
While your code is indeed more readable, I think the current code is still within the spec: UA2005 chap 7.59: "Note: Execution of an LDTWA instruction with rd = 0 modifies only R[1]." -- Regards, Artyom Tarasenko SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu
