On Mon, Oct 31, 2016 at 5:32 PM, Richard Henderson <r...@twiddle.net> wrote: > On 10/31/2016 10:21 AM, Artyom Tarasenko wrote: >> >> 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]." > > > What I mean is found in the description of LDTWA (looking at ua2011 here): > > # Nontranslating ASIs (see page 395) should only be accessed > # using LDXA (not LDTWA) instructions. If an LDTWA > # referencing a nontranslating ASI is executed, per the above > # table, it generates a DAE_invalid_asi exception > # (impl. dep. #300-U4-Cs10). > > ASI_IC_TAG is certainly nontranslating ASI. > > All of the translating ASIs supported by LDTXA are already handled by > GET_ASI_DTWINX; all of the translating ASIs supported by LDTWA are already > handled by GET_ASI_DIRECT. By that reading the "default:" case should > simply raise DAE_invalid_asi. >
Interesting. The US2 spec says that ASI_IC_TAG is "LDDA, STDFA or STXA only. Other types of access cause a data_access_exception trap." -- Regards, Artyom Tarasenko SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu
