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SubjectRe: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)
Steven Rostedt wrote:
> On Wed, 20 Aug 2008, Steven Rostedt wrote:
>
>
>> On Wed, 20 Aug 2008, Benjamin Herrenschmidt wrote:
>>
>>
>>> Found the problem (or at least -a- problem), it's a gcc bug.
>>>
>>> Well, first I must say the code generated by -pg is just plain
>>> horrible :-)
>>>
>>> Appart from that, look at the exit of, for example, __d_lookup, as
>>> generated by gcc when ftrace is enabled:
>>>
>>> c00c0498: 38 60 00 00 li r3,0
>>> c00c049c: 81 61 00 00 lwz r11,0(r1)
>>> c00c04a0: 80 0b 00 04 lwz r0,4(r11)
>>> c00c04a4: 7d 61 5b 78 mr r1,r11
>>> c00c04a8: bb 0b ff e0 lmw r24,-32(r11)
>>> c00c04ac: 7c 08 03 a6 mtlr r0
>>> c00c04b0: 4e 80 00 20 blr
>>>
>>> As you can see, it restores r1 -before- it pops r24..r31 off
>>> the stack ! I let you imagine what happens if an interrupt happens
>>> just in between those two instructions (mr and lmw). We don't do
>>> redzones on our ABI, so basically, the registers end up corrupted
>>> by the interrupt.
>>>
>> Ouch! You've disassembled this without -pg too, and it does not have this
>> bug? What version of gcc do you have?
>>
>>
>
> I have:
> gcc (Debian 4.3.1-2) 4.3.1
>
> c00c64c8: 81 61 00 00 lwz r11,0(r1)
> c00c64cc: 7f 83 e3 78 mr r3,r28
> c00c64d0: 80 0b 00 04 lwz r0,4(r11)
> c00c64d4: ba eb ff dc lmw r23,-36(r11)
> c00c64d8: 7d 61 5b 78 mr r1,r11
> c00c64dc: 7c 08 03 a6 mtlr r0
> c00c64e0: 4e 80 00 20 blr
>
>
> My version looks fine. I'm thinking that this is a separate issue than
> what Eran is seeing.
>
> Eran, can you do an "objdump -dr vmlinux" and search for __d_lookup, and
> print out the end of the function dump.
>
> Thanks,
>
> -- Steve
>
>
>
>
powerpc-linux-gnu-objdump -dr --start-address=0xc00bb584 vmlinux | head
-n 100

vmlinux: file format elf32-powerpc

Disassembly of section .text:

c00bb584 <__d_lookup>:
c00bb584: 7c 08 02 a6 mflr r0
c00bb588: 90 01 00 04 stw r0,4(r1)
c00bb58c: 4b f5 5c 51 bl c00111dc <_mcount>
c00bb590: 94 21 ff d0 stwu r1,-48(r1)
c00bb594: 7c 08 02 a6 mflr r0
c00bb598: 3d 20 9e 37 lis r9,-25033
c00bb59c: bf 01 00 10 stmw r24,16(r1)
c00bb5a0: 61 29 00 01 ori r9,r9,1
c00bb5a4: 3d 60 c0 38 lis r11,-16328
c00bb5a8: 90 01 00 34 stw r0,52(r1)
c00bb5ac: 7c 60 4a 78 xor r0,r3,r9
c00bb5b0: 54 00 d9 7e rlwinm r0,r0,27,5,31
c00bb5b4: 83 84 00 00 lwz r28,0(r4)
c00bb5b8: 7c 3f 0b 78 mr r31,r1
c00bb5bc: 81 0b 1a 2c lwz r8,6700(r11)
c00bb5c0: 39 6b 1a 2c addi r11,r11,6700
c00bb5c4: 7c 00 e2 14 add r0,r0,r28
c00bb5c8: 81 4b 00 04 lwz r10,4(r11)
c00bb5cc: 7c 09 4a 78 xor r9,r0,r9
c00bb5d0: 83 24 00 04 lwz r25,4(r4)
c00bb5d4: 7d 29 44 30 srw r9,r9,r8
c00bb5d8: 81 0b 00 08 lwz r8,8(r11)
c00bb5dc: 7d 29 02 78 xor r9,r9,r0
c00bb5e0: 83 04 00 08 lwz r24,8(r4)
c00bb5e4: 7d 29 50 38 and r9,r9,r10
c00bb5e8: 55 29 10 3a rlwinm r9,r9,2,0,29
c00bb5ec: 7c 09 40 2e lwzx r0,r9,r8
c00bb5f0: 7c 9a 23 78 mr r26,r4
c00bb5f4: 7c 7b 1b 78 mr r27,r3
c00bb5f8: 2f 80 00 00 cmpwi cr7,r0,0
c00bb5fc: 7c 1e 03 78 mr r30,r0
c00bb600: 40 be 00 14 bne+ cr7,c00bb614 <__d_lookup+0x90>
c00bb604: 48 00 00 7c b c00bb680 <__d_lookup+0xfc>
c00bb608: 83 de 00 00 lwz r30,0(r30)
c00bb60c: 2f 9e 00 00 cmpwi cr7,r30,0
c00bb610: 41 9e 00 70 beq- cr7,c00bb680 <__d_lookup+0xfc>
c00bb614: 80 1e 00 00 lwz r0,0(r30)
c00bb618: 2f 80 00 00 cmpwi cr7,r0,0
c00bb61c: 41 9e 00 08 beq- cr7,c00bb624 <__d_lookup+0xa0>
c00bb620: 7c 00 02 2c dcbt r0,r0
c00bb624: 3b be ff f4 addi r29,r30,-12
c00bb628: 80 1d 00 18 lwz r0,24(r29)
c00bb62c: 7f 80 e0 00 cmpw cr7,r0,r28
c00bb630: 40 9e ff d8 bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb634: 80 1d 00 14 lwz r0,20(r29)
c00bb638: 7f 80 d8 00 cmpw cr7,r0,r27
c00bb63c: 40 9e ff cc bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb640: 81 3b 00 48 lwz r9,72(r27)
c00bb644: 38 9d 00 18 addi r4,r29,24
c00bb648: 2f 89 00 00 cmpwi cr7,r9,0
c00bb64c: 41 9e 00 50 beq- cr7,c00bb69c <__d_lookup+0x118>
c00bb650: 80 09 00 08 lwz r0,8(r9)
c00bb654: 2f 80 00 00 cmpwi cr7,r0,0
c00bb658: 41 9e 00 44 beq- cr7,c00bb69c <__d_lookup+0x118>
c00bb65c: 7f 63 db 78 mr r3,r27
c00bb660: 7c 09 03 a6 mtctr r0
c00bb664: 7f 45 d3 78 mr r5,r26
c00bb668: 4e 80 04 21 bctrl
c00bb66c: 2f 83 00 00 cmpwi cr7,r3,0
c00bb670: 41 9e 00 50 beq- cr7,c00bb6c0 <__d_lookup+0x13c>
c00bb674: 83 de 00 00 lwz r30,0(r30)
c00bb678: 2f 9e 00 00 cmpwi cr7,r30,0
c00bb67c: 40 9e ff 98 bne+ cr7,c00bb614 <__d_lookup+0x90>
c00bb680: 38 60 00 00 li r3,0
c00bb684: 81 61 00 00 lwz r11,0(r1)
c00bb688: 80 0b 00 04 lwz r0,4(r11)
c00bb68c: 7d 61 5b 78 mr r1,r11
c00bb690: bb 0b ff e0 lmw r24,-32(r11)
c00bb694: 7c 08 03 a6 mtlr r0
c00bb698: 4e 80 00 20 blr
c00bb69c: 80 04 00 04 lwz r0,4(r4)
c00bb6a0: 7f 80 c8 00 cmpw cr7,r0,r25
c00bb6a4: 40 9e ff 64 bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb6a8: 80 64 00 08 lwz r3,8(r4)
c00bb6ac: 7f 25 cb 78 mr r5,r25
c00bb6b0: 7f 04 c3 78 mr r4,r24
c00bb6b4: 4b f5 ab 65 bl c0016218 <memcmp>
c00bb6b8: 2f 83 00 00 cmpwi cr7,r3,0
c00bb6bc: 40 9e ff 4c bne+ cr7,c00bb608 <__d_lookup+0x84>
c00bb6c0: 80 1d 00 04 lwz r0,4(r29)
c00bb6c4: 70 09 00 10 andi. r9,r0,16
c00bb6c8: 40 a2 ff b8 bne- c00bb680 <__d_lookup+0xfc>
c00bb6cc: 7c 00 e8 28 lwarx r0,0,r29
c00bb6d0: 30 00 00 01 addic r0,r0,1
c00bb6d4: 7c 00 e9 2d stwcx. r0,0,r29
c00bb6d8: 40 a2 ff f4 bne- c00bb6cc <__d_lookup+0x148>
c00bb6dc: 7f a3 eb 78 mr r3,r29
c00bb6e0: 4b ff ff a4 b c00bb684 <__d_lookup+0x100>

c00bb6e4 <d_lookup>:
c00bb6e4: 7c 08 02 a6 mflr r0
c00bb6e8: 90 01 00 04 stw r0,4(r1)



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