On Wed, 2014-12-17 at 10:27 +0100, Alexander Graf wrote: > > On 17.12.14 04:44, Anton Blanchard wrote: > > Hi Alex, > > > >> Git bisect managed to point me to this commit as the offender for > >> OOPSes on e5500 and e6500 (and maybe the G4 as well, not sure). > >> > >> Doing a git revert of this commit on top of linus/master makes things > >> work fine for me again. > > > > Ouch, sorry for that, I'll work to reproduce. What gcc version are you > > using? > > I'm running > > gcc (SUSE Linux) 4.7.2 20130108 [gcc-4_7-branch revision 195012] > > which is basically the one from openSUSE 12.3 for ppc64.
OK. I've also reproduced it with what I think is stock 4.7.3. I only see it in __skb_checksum() though, which is a bit odd. It is a fairly large routine, so maybe it's just register pressure? I tried for a while to create a self contained test case, but couldn't get anything to work. I guess we'll have to revert the kernel patch, unless someone can identify the gcc bug soon. I also wonder if it's fixed in later versions, or we're just not seeing it due to good luck. Below is the broken vs working code. For some reason in the bad case it backs up r1, as if it thinks it will be clobbered by the rldicr. Bad: c00000000076df84: 7c 29 0b 78 mr r9,r1 <-- save of r1 ? c00000000076df88: 78 27 04 64 rldicr r7,r1,0,49 <-- current_thread_info() c00000000076df8c: 7d 08 ea 14 add r8,r8,r29 c00000000076df90: 7c 9f 40 50 subf r4,r31,r8 c00000000076df94: 7d 12 07 b4 extsw r18,r8 c00000000076df98: 2f 04 00 00 cmpwi cr6,r4,0 c00000000076df9c: 7c 9c 23 78 mr r28,r4 c00000000076dfa0: 7f 84 f0 00 cmpw cr7,r4,r30 c00000000076dfa4: 40 99 00 cc ble- cr6,c00000000076e070 <.__skb_checksum+0x220> c00000000076dfa8: 40 9d 00 08 ble- cr7,c00000000076dfb0 <.__skb_checksum+0x160> c00000000076dfac: 7f dc f3 78 mr r28,r30 c00000000076dfb0: 81 07 00 14 lwz r8,20(r7) c00000000076dfb4: e8 6a 00 00 ld r3,0(r10) c00000000076dfb8: 7f 94 07 b4 extsw r20,r28 c00000000076dfbc: 39 08 00 01 addi r8,r8,1 c00000000076dfc0: 91 07 00 14 stw r8,20(r7) c00000000076dfc4: 7c 63 b2 14 add r3,r3,r22 c00000000076dfc8: 7e 84 a3 78 mr r4,r20 c00000000076dfcc: 7c 63 1e 74 sradi r3,r3,3 c00000000076dfd0: 38 a0 00 00 li r5,0 c00000000076dfd4: 7c 63 c1 d2 mulld r3,r3,r24 c00000000076dfd8: 81 0a 00 08 lwz r8,8(r10) c00000000076dfdc: 7d 1f 42 14 add r8,r31,r8 c00000000076dfe0: 78 63 83 e4 rldicr r3,r3,16,47 c00000000076dfe4: 7f bd 40 50 subf r29,r29,r8 c00000000076dfe8: 7c 63 bb 78 or r3,r3,r23 c00000000076dfec: 7c 63 ea 14 add r3,r3,r29 c00000000076dff0: e9 59 00 00 ld r10,0(r25) c00000000076dff4: e9 0a 00 00 ld r8,0(r10) c00000000076dff8: f8 49 00 28 std r2,40(r9) <-- use of r9 which is OK c00000000076dffc: 7d 09 03 a6 mtctr r8 c00000000076e000: e8 4a 00 08 ld r2,8(r10) c00000000076e004: 4e 80 04 21 bctrl c00000000076e008: e8 49 00 28 ld r2,40(r9) <-- but not OK here Good: c00000000076e0b0: 78 39 04 64 rldicr r25,r1,0,49 <-- current_thread_info() c00000000076e0b4: 7a 94 07 c6 rldicr r20,r20,32,31 c00000000076e0b8: 62 d6 6d b7 ori r22,r22,28087 c00000000076e0bc: 7a b5 00 44 rldicr r21,r21,0,1 c00000000076e0c0: 7d 5f f2 14 add r10,r31,r30 c00000000076e0c4: 39 1a 00 03 addi r8,r26,3 c00000000076e0c8: 79 08 26 e4 rldicr r8,r8,4,59 c00000000076e0cc: 7f 8a e8 00 cmpw cr7,r10,r29 c00000000076e0d0: 7d 40 00 26 mfcr r10 c00000000076e0d4: 55 4a ef fe rlwinm r10,r10,29,31,31 c00000000076e0d8: 7d 29 42 14 add r9,r9,r8 c00000000076e0dc: 0b 0a 00 00 tdnei r10,0 c00000000076e0e0: 81 49 00 0c lwz r10,12(r9) c00000000076e0e4: 7d 4a ea 14 add r10,r10,r29 c00000000076e0e8: 7d 1f 50 50 subf r8,r31,r10 c00000000076e0ec: 7d 51 07 b4 extsw r17,r10 c00000000076e0f0: 2f 08 00 00 cmpwi cr6,r8,0 c00000000076e0f4: 7d 1c 43 78 mr r28,r8 c00000000076e0f8: 7f 88 f0 00 cmpw cr7,r8,r30 c00000000076e0fc: 40 99 00 c8 ble- cr6,c00000000076e1c4 <.__skb_checksum+0x214> c00000000076e100: 40 9d 00 08 ble- cr7,c00000000076e108 <.__skb_checksum+0x158> c00000000076e104: 7f dc f3 78 mr r28,r30 c00000000076e108: 81 59 00 14 lwz r10,20(r25) c00000000076e10c: e8 69 00 00 ld r3,0(r9) c00000000076e110: 7f 93 07 b4 extsw r19,r28 c00000000076e114: 39 4a 00 01 addi r10,r10,1 c00000000076e118: 91 59 00 14 stw r10,20(r25) c00000000076e11c: 7c 63 a2 14 add r3,r3,r20 c00000000076e120: 7e 64 9b 78 mr r4,r19 c00000000076e124: 7c 63 1e 74 sradi r3,r3,3 c00000000076e128: 38 a0 00 00 li r5,0 c00000000076e12c: 7c 63 b1 d2 mulld r3,r3,r22 c00000000076e130: 81 49 00 08 lwz r10,8(r9) c00000000076e134: 7d 5f 52 14 add r10,r31,r10 c00000000076e138: 78 63 83 e4 rldicr r3,r3,16,47 c00000000076e13c: 7f bd 50 50 subf r29,r29,r10 c00000000076e140: 7c 63 ab 78 or r3,r3,r21 c00000000076e144: 7c 63 ea 14 add r3,r3,r29 c00000000076e148: e9 37 00 00 ld r9,0(r23) c00000000076e14c: e9 49 00 00 ld r10,0(r9) c00000000076e150: f8 41 00 28 std r2,40(r1) <-- correct use of r1 c00000000076e154: 7d 49 03 a6 mtctr r10 c00000000076e158: e8 49 00 08 ld r2,8(r9) c00000000076e15c: 4e 80 04 21 bctrl c00000000076e160: e8 41 00 28 ld r2,40(r1) <-- correct use of r1 cheers _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
