From: Michael Ellerman <mpe@ellerman•id.au>
To: Alexander Graf <agraf@suse•de>
Cc: ulrich.weigand@de•ibm.com, paulus@samba•org,
Anton Blanchard <anton@samba•org>,
Scott Wood <scottwood@freescale•com>,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH 1/3] powerpc: Don't use local named register variable in current_thread_info
Date: Mon, 22 Dec 2014 17:49:04 +1100 [thread overview]
Message-ID: <1419230944.20221.6.camel@ellerman.id.au> (raw)
In-Reply-To: <54914C85.30107@suse.de>
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
next prev parent reply other threads:[~2014-12-22 6:49 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1414727247-31838-1-git-send-email-anton__19440.5086375356$1414727300$gmane$org@samba.org>
2014-12-17 1:16 ` [PATCH 1/3] powerpc: Don't use local named register variable in current_thread_info Alexander Graf
2014-12-17 3:44 ` Anton Blanchard
2014-12-17 9:27 ` Alexander Graf
2014-12-22 6:49 ` Michael Ellerman [this message]
2014-12-18 5:11 ` Michael Ellerman
2014-12-18 6:25 ` Anton Blanchard
2014-12-18 15:02 ` Alexander Graf
2014-12-31 12:24 ` Alan Modra
2015-01-07 5:12 ` Anton Blanchard
2015-01-07 17:59 ` Scott Wood
2015-01-08 6:36 ` Alan Modra
2014-12-18 14:56 ` Alexander Graf
2014-10-31 3:47 Anton Blanchard
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