Resending: RT patches expose netdev race [was Re: [RFC] [patch 2/2] powerpc 2.6.21-rt1: fix kernel hang and/or panic

From: Linas Vepstas
Date: Wed May 16 2007 - 20:28:52 EST

(resending , Owa-san was cut from cc list!??)

Hi,

On Tue, May 15, 2007 at 08:09:02PM +1000, Benjamin Herrenschmidt wrote:
> On Tue, 2007-05-15 at 17:47 +0900, Tsutomu OWA wrote:
> > I encountered the following error when doing netperf from other machine
> > to Celleb running RT kernel. PREEPT_NONE kernel works just fine as well.
>
> Hrm... sounds a bit weird. I wonder if there's a locking bug in the
> driver in the first place.
>
> Linas, what's your take ?

Heh. I almost deleted the entire email thread cause it
didn't say "spidernet" in the subject line. :-)
Seriously, I really almost did ....

Since this is a long email; let me put a summary up front:
I think the RT/premption patches are exposing some sort
of race in the ip header handling code. The rest of the
note is forensics pointing to this.

----

Reading the patch, it looks like all it did was to move
around the locks, without changing the semantics. Two
comments about that:

-- The current spidernet locks are very fine-grained;
this makes the whole thing function more smoothly.
The patch would make them coarse-grained, I don't
like that.

-- Moving around locks like that changes the timing
completely, and changing the timing makes races
come and go. The races seem to vanish, but that's
only cause you are getting lucky.

Since I'm sick-n-tired of dealing with spidernet, I thought
I'd give this one a little extra attention.

The crash is a null pointer deref. The spidernet doesn't
use locks to protect null pointers. The spidernet mostly
doesn't play with pointers at all; they're mostly static.
So this crash is "unusual" from the get-go.

>> Instruction dump:
>> 60000000 81790088 901f000c 913f0018 913f0008 917f0004 48132e8d
>> 60000000
>> a019009e 2f800800 409e0038 e9390038 <88690009> 2f830006 419e0010
>> 2f830011

The crashing instruction is <88690009> which is very unique:
lbz r3,9(r9)

load byte ... at an offset of 9 bytes!? spidernet does
nothing with bytes, so its another reason its not spidernet.

Below follows a manual disassembly. The guilty party appears
to the the skb, and spcifically, skb->head has not been set.
You'll have to read the details below to see why.

I do not know why sk_buff->head would be null, or
would be set in a racy kind of way, or why the rt patches
would cause this. But the evidence implicates that.

--linas

Long stuff below. For the record:

> > Unable to handle kernel paging request for data at address 0x00000009
> > Faulting instruction address: 0xc000000000295434
> > Oops: Kernel access of bad area, sig: 11 [#1]
> > PREEMPT SMP NR_CPUS=2 NUMA
> > Modules linked in:
> > NIP: C000000000295434 LR: C000000000295420 CTR: 0000000000000000
> > REGS: c0000000095d6e30 TRAP: 0300 Not tainted (2.6.21-rc5-rt7)
> > MSR: 8000000000009032 <EE,ME,IR,DR> CR: 24000482 XER: 20000000
> > DAR: 0000000000000009, DSISR: 0000000040000000
> > TASK = c000000001e7c440[626] 'netserver' THREAD: c0000000095d4000 CPU: 0
> > GPR00: 0000000000000800 C0000000095D70B0 C0000000005D77B8 0000000000000001
> > GPR04: 0000000000000001 0000000000000000 C0000000095D7080 0000000000000000
> > GPR08: C0000000095D7030 0000000000000000 C0000000095D7040 0000000000000000
> > GPR12: FC69925300080D5D C0000000004DE680 0000000000000000 0000000000422208
> > GPR16: 0000000000400000 0000000000420D10 0000000000000000 C0000000095D7C88
> > GPR20: C000000001E7C440 0000000000000000 0000000000000001 C000000008ACEAE0
> > GPR24: 0000000000000020 C000000000E50C80 0000000081F84C5E C000000001C00BE0
> > GPR28: C000000001C05430 C000000001C00B80 C000000000570F30 C000000001FD1720
> > NIP [C000000000295434] .spider_net_xmit+0x1dc/0x448
> > LR [C000000000295420] .spider_net_xmit+0x1c8/0x448
> > Call Trace:
> > [C0000000095D70B0] [C000000000295420] .spider_net_xmit+0x1c8/0x448 (unreliable)
> > [C0000000095D7160] [C000000000327EE8] .dev_hard_start_xmit+0x238/0x300
> > [C0000000095D7200] [C00000000033A7F4] .__qdisc_run+0xdc/0x2a4
> > [C0000000095D72B0] [C00000000032A948] .dev_queue_xmit+0x1b0/0x2fc
> > [C0000000095D7350] [C00000000034B470] .ip_output+0x280/0x2d8
> > [C0000000095D73F0] [C00000000034C6CC] .ip_queue_xmit+0x448/0x4d8
> > [C0000000095D74F0] [C00000000035F6D8] .tcp_transmit_skb+0x850/0x8c0
> > [C0000000095D75C0] [C00000000035C394] .__tcp_ack_snd_check+0x84/0xc0
> > [C0000000095D7650] [C00000000035E114] .tcp_rcv_established+0x4f0/0x8ac
> > [C0000000095D7700] [C000000000365B24] .tcp_v4_do_rcv+0x5c/0x448
> > [C0000000095D77D0] [C00000000031C2C4] .release_sock+0x94/0x11c
> > [C0000000095D7870] [C000000000354E7C] .tcp_recvmsg+0x374/0x8d8
> > [C0000000095D7960] [C00000000031B8A0] .sock_common_recvmsg+0x5c/0x84
> > [C0000000095D79F0] [C00000000031921C] .sock_recvmsg+0x110/0x15c
> > [C0000000095D7C00] [C00000000031AA50] .sys_recvfrom+0xf0/0x174
> > [C0000000095D7D90] [C000000000339368] .compat_sys_socketcall+0x178/0x214
> > [C0000000095D7E30] [C000000000008634] syscall_exit+0x0/0x40
> > Instruction dump:
> > 60000000 81790088 901f000c 913f0018 913f0008 917f0004 48132e8d 60000000
> > a019009e 2f800800 409e0038 e9390038 <88690009> 2f830006 419e0010 2f830011
> >

spider_net.o: file format elf64-powerpc
Disassembly of section .text:


Below is the full disassembly of spider_net_xmit()
Note that the compiler has inlined spider_net_prepare_tx_descr()
which makes it somewhat harder to read. Disassembly picks
up in the middle of spider_net_prepare_tx_descr(), below.

My compiler generated slightly different code than Tsutomu
so the offsets are a little off, but the crashing instruction
is so unique, its easy to find. I got lucky :-)

000000000000313c <.spider_net_xmit>:
313c: 7c 08 02 a6 mflr r0
3140: fb 21 ff c8 std r25,-56(r1)
3144: fb 61 ff d8 std r27,-40(r1)
3148: fb a1 ff e8 std r29,-24(r1)
314c: fb c1 ff f0 std r30,-16(r1)
3150: fb e1 ff f8 std r31,-8(r1)
3154: fb 41 ff d0 std r26,-48(r1)
3158: f8 01 00 10 std r0,16(r1)
315c: fb 81 ff e0 std r28,-32(r1)
3160: f8 21 ff 51 stdu r1,-176(r1)
3164: eb c2 00 00 ld r30,0(r2)
3168: 3b a4 07 80 addi r29,r4,1920
316c: 7c 79 1b 78 mr r25,r3
3170: 7c 9f 23 78 mr r31,r4
3174: 7f a3 eb 78 mr r3,r29
3178: 38 80 00 00 li r4,0
317c: 3b 7f 07 e0 addi r27,r31,2016
3180: 4b ff e1 d1 bl 1350 <.spider_net_release_tx_chain>
3184: e8 1d 00 08 ld r0,8(r29)
3188: e8 99 00 b0 ld r4,176(r25)
318c: 38 60 00 00 li r3,0
3190: 80 b9 00 70 lwz r5,112(r25)
3194: 2f a0 00 00 cmpdi cr7,r0,0
3198: 41 9e 00 1c beq- cr7,31b4 <.spider_net_xmit+0x78>
319c: 34 60 00 70 addic. r3,r0,112
31a0: 41 82 00 14 beq- 31b4 <.spider_net_xmit+0x78>
31a4: e8 03 02 30 ld r0,560(r3)
31a8: 2f a0 00 00 cmpdi cr7,r0,0
31ac: 7c 09 03 78 mr r9,r0
31b0: 40 9e 00 08 bne- cr7,31b8 <.spider_net_xmit+0x7c>
31b4: 39 20 00 00 li r9,0
31b8: 7d 20 00 74 cntlzd r0,r9
31bc: 78 00 d1 82 rldicl r0,r0,58,6
31c0: 0b 00 00 00 tdnei r0,0
31c4: e9 29 00 10 ld r9,16(r9)
31c8: 38 c0 00 01 li r6,1
31cc: e8 09 00 00 ld r0,0(r9)
31d0: f8 41 00 28 std r2,40(r1)
31d4: 7c 09 03 a6 mtctr r0
31d8: e9 69 00 10 ld r11,16(r9)
31dc: e8 49 00 08 ld r2,8(r9)
31e0: 4e 80 04 21 bctrl
31e4: e8 41 00 28 ld r2,40(r1)
31e8: 2f a3 ff ff cmpdi cr7,r3,-1
31ec: 7c 7a 1b 78 mr r26,r3
31f0: 40 9e 00 44 bne- cr7,3234 <.spider_net_xmit+0xf8>
31f4: e8 1d 01 82 lwa r0,384(r29)
31f8: 78 09 cf e3 rldicl. r9,r0,57,63
31fc: 41 82 00 28 beq- 3224 <.spider_net_xmit+0xe8>
3200: 48 00 00 01 bl 3200 <.spider_net_xmit+0xc4>
3204: 60 00 00 00 nop
3208: 2f a3 00 00 cmpdi cr7,r3,0
320c: 41 9e 00 18 beq- cr7,3224 <.spider_net_xmit+0xe8>
3210: e8 7e 82 80 ld r3,-32128(r30)
3214: 80 b9 00 70 lwz r5,112(r25)
3218: e8 99 00 b0 ld r4,176(r25)
321c: 48 00 00 01 bl 321c <.spider_net_xmit+0xe0>
3220: 60 00 00 00 nop
3224: e9 3d 02 60 ld r9,608(r29)
3228: 39 29 00 01 addi r9,r9,1
322c: f9 3d 02 60 std r9,608(r29)
3230: 48 00 01 6c b 339c <.spider_net_xmit+0x260>
3234: 7f 63 db 78 mr r3,r27
3238: 48 00 00 01 bl 3238 <.spider_net_xmit+0xfc>
323c: 60 00 00 00 nop
3240: eb 9d 00 68 ld r28,104(r29)
3244: e9 3b 00 10 ld r9,16(r27)
3248: 7c 64 1b 78 mr r4,r3
324c: e9 7c 00 18 ld r11,24(r28)
3250: e8 09 00 20 ld r0,32(r9)
3254: 7f ab 00 00 cmpd cr7,r11,r0
3258: 40 9e 00 78 bne- cr7,32d0 <.spider_net_xmit+0x194>
325c: 7f 63 db 78 mr r3,r27
3260: 48 00 00 01 bl 3260 <.spider_net_xmit+0x124>
3264: 60 00 00 00 nop
3268: e8 1d 00 08 ld r0,8(r29)
326c: 80 b9 00 70 lwz r5,112(r25)
3270: 38 60 00 00 li r3,0
3274: 2f a0 00 00 cmpdi cr7,r0,0
3278: 41 9e 00 1c beq- cr7,3294 <.spider_net_xmit+0x158>
327c: 34 60 00 70 addic. r3,r0,112
3280: 41 82 00 14 beq- 3294 <.spider_net_xmit+0x158>
3284: e8 03 02 30 ld r0,560(r3)
3288: 2f a0 00 00 cmpdi cr7,r0,0
328c: 7c 09 03 78 mr r9,r0
3290: 40 9e 00 08 bne- cr7,3298 <.spider_net_xmit+0x15c>
3294: 39 20 00 00 li r9,0
3298: 7d 20 00 74 cntlzd r0,r9
329c: 78 00 d1 82 rldicl r0,r0,58,6
32a0: 0b 00 00 00 tdnei r0,0
32a4: e9 29 00 18 ld r9,24(r9)
32a8: 7f 44 d3 78 mr r4,r26
32ac: 38 c0 00 01 li r6,1
32b0: e8 09 00 00 ld r0,0(r9)
32b4: f8 41 00 28 std r2,40(r1)
32b8: 7c 09 03 a6 mtctr r0
32bc: e9 69 00 10 ld r11,16(r9)
32c0: e8 49 00 08 ld r2,8(r9)
32c4: 4e 80 04 21 bctrl
32c8: e8 41 00 28 ld r2,40(r1)
32cc: 48 00 00 d0 b 339c <.spider_net_xmit+0x260>
32d0: eb fc 00 00 ld r31,0(r28)
32d4: f9 7b 00 08 std r11,8(r27)
32d8: 3c 00 a0 04 lis r0,-24572
32dc: 39 60 00 00 li r11,0
32e0: fb 3c 00 08 std r25,8(r28)
32e4: 7f 63 db 78 mr r3,r27
32e8: 93 5f 00 00 stw r26,0(r31)
32ec: 60 00 00 00 nop

r25 points to struct sk_buff * skb

32f0: 81 39 00 70 lwz r9,112(r25) skb->len
32f4: 90 1f 00 0c stw r0,12(r31) dmac_cmd_status;
32f8: 91 7f 00 18 stw r11,24(r31) data_status;
32fc: 91 7f 00 08 stw r11,8(r31) next_descr_addr;
3300: 91 3f 00 04 stw r9,4(r31) buf_size;

r31 is ptr to struct spider_net_hw_descr * hwdescr
above insns are
hwdescr->buf_addr = buf;
hwdescr->buf_size = skb->len;
hwdescr->next_descr_addr = 0;
hwdescr->data_status = 0;


3304: 48 00 00 01 bl 3304 <.spider_net_xmit+0x1c8>
3308: 60 00 00 00 nop
bl to spin_unlock_irqrestore() ?!

r25 is skb and 128(skb) is ip_summed and the
next 7 insn's bit flag manipulation to pull this out.

330c: e8 19 00 80 ld r0,128(r25)
3310: 3d 20 30 00 lis r9,12288
3314: 61 29 08 00 ori r9,r9,2048
3318: 78 00 23 02 rldicl r0,r0,36,12
331c: 78 00 e0 a0 rldicl r0,r0,28,34
3320: 7f a0 48 00 cmpd cr7,r0,r9
3324: 40 9e 00 40 bne- cr7,3364 <.spider_net_xmit+0x228>

Now the case statement, which is several inlines:
switch (ip_hdr(skb)->protocol) {

static inline struct iphdr *ip_hdr(const struct sk_buff *skb)
{
return (struct iphdr *)skb_network_header(skb);
}
static inline unsigned char *skb_network_header(const struct sk_buff
*skb)
{
return skb->head + skb->network_header;
}

3328: 80 19 00 98 lwz r0,152(r25) skb->network_header
332c: e9 39 00 a8 ld r9,168(r25) skb->head
3330: 7d 29 02 14 add r9,r9,r0 skb->head + skb->network_header;
3334: 88 69 00 09 lbz r3,9(r9) struct iphdr ->protocol

crash here , r9 is null

__u8 protocol; is exactly 9 bytes into struct iphdr


switch (ip_hdr(skb)->protocol) {
3338: 2f 83 00 06 cmpwi cr7,r3,6
333c: 41 9e 00 10 beq- cr7,334c <.spider_net_xmit+0x210>
3340: 2f 83 00 11 cmpwi cr7,r3,17

3344: 40 9e 00 20 bne- cr7,3364 <.spider_net_xmit+0x228>
3348: 48 00 00 10 b 3358 <.spider_net_xmit+0x21c>

case IPPROTO_TCP:
334c: 80 1f 00 0c lwz r0,12(r31)

hwdescr->dmac_cmd_status |= SPIDER_NET_DMAC_TCP;
3350: 64 00 00 02 oris r0,r0,2
3354: 48 00 00 0c b 3360 <.spider_net_xmit+0x224>
case IPPROTO_UDP:
3358: 80 1f 00 0c lwz r0,12(r31)
hwdescr->dmac_cmd_status |= SPIDER_NET_DMAC_UDP;
335c: 64 00 00 03 oris r0,r0,3
3360: 90 1f 00 0c stw r0,12(r31)
wmb()
3364: 7c 00 04 ac sync

3368: e9 3c 00 20 ld r9,32(r28)
336c: 80 1c 00 10 lwz r0,16(r28)
3370: 3b 80 00 00 li r28,0
3374: e9 7e 80 78 ld r11,-32648(r30)
3378: e9 29 00 00 ld r9,0(r9)
337c: 90 09 00 08 stw r0,8(r9)
3380: 60 00 00 00 nop
3384: e8 0b 00 00 ld r0,0(r11)
3388: e9 3d 00 00 ld r9,0(r29)
338c: f8 09 03 18 std r0,792(r9)
3390: 60 00 00 00 nop
3394: e9 7d 00 70 ld r11,112(r29)
3398: 48 00 00 5c b 33f4 <.spider_net_xmit+0x2b8>
339c: e9 7d 01 c0 ld r11,448(r29)
33a0: 39 3f 00 40 addi r9,r31,64
33a4: 38 00 00 01 li r0,1
33a8: 39 6b 00 01 addi r11,r11,1
33ac: f9 7d 01 c0 std r11,448(r29)
33b0: 60 00 00 00 nop
33b4: 60 00 00 00 nop
33b8: 60 00 00 00 nop
33bc: 7d 60 48 a8 ldarx r11,0,r9
33c0: 7d 6b 03 78 or r11,r11,r0
33c4: 7d 60 49 ad stdcx. r11,0,r9
33c8: 40 a2 ff f4 bne- 33bc <.spider_net_xmit+0x280>
33cc: 38 60 00 01 li r3,1
33d0: 48 00 01 a0 b 3570 <.spider_net_xmit+0x434>
33d4: e9 2b 00 00 ld r9,0(r11)
33d8: 80 09 00 0c lwz r0,12(r9)
33dc: 3d 20 f0 00 lis r9,-4096
33e0: 54 00 00 06 rlwinm r0,r0,0,0,3
33e4: 7f 80 48 00 cmpw cr7,r0,r9
33e8: 41 9e 00 1c beq- cr7,3404 <.spider_net_xmit+0x2c8>
33ec: e9 6b 00 18 ld r11,24(r11)
33f0: 7d 5c 07 b4 extsw r28,r10
33f4: e8 1d 00 68 ld r0,104(r29)
33f8: 39 5c 00 01 addi r10,r28,1
33fc: 7f ab 00 00 cmpd cr7,r11,r0
3400: 40 9e ff d4 bne+ cr7,33d4 <.spider_net_xmit+0x298>
3404: 80 1d 00 80 lwz r0,128(r29)
3408: 7c 00 16 70 srawi r0,r0,2
340c: 7c 00 01 94 addze r0,r0
3410: 7f 80 e0 00 cmpw cr7,r0,r28
3414: 41 9d 00 a4 bgt- cr7,34b8 <.spider_net_xmit+0x37c>
3418: 1c 1c 00 03 mulli r0,r28,3
341c: eb fd 00 70 ld r31,112(r29)
3420: 7c 00 16 70 srawi r0,r0,2
3424: 7c 00 01 94 addze r0,r0
3428: 7c 1c 07 b4 extsw r28,r0
342c: 2f 9c 00 00 cmpwi cr7,r28,0
3430: 7b 89 00 20 clrldi r9,r28,32
3434: 39 29 00 01 addi r9,r9,1
3438: 7d 29 03 a6 mtctr r9
343c: 41 9c 00 10 blt- cr7,344c <.spider_net_xmit+0x310>
3440: 3c 00 80 00 lis r0,-32768
3444: 7f 9c 00 00 cmpw cr7,r28,r0
3448: 40 be 00 14 bne+ cr7,345c <.spider_net_xmit+0x320>
344c: 38 00 00 01 li r0,1
3450: 7c 09 03 a6 mtctr r0
3454: 48 00 00 08 b 345c <.spider_net_xmit+0x320>
3458: eb ff 00 18 ld r31,24(r31)
345c: 42 00 ff fc bdnz+ 3458 <.spider_net_xmit+0x31c>
3460: 38 7d 00 60 addi r3,r29,96
3464: 48 00 00 01 bl 3464 <.spider_net_xmit+0x328>
3468: 60 00 00 00 nop
346c: e9 3f 00 00 ld r9,0(r31)
3470: 80 09 00 0c lwz r0,12(r9)
3474: 64 00 00 80 oris r0,r0,128
3478: 90 09 00 0c stw r0,12(r9)
347c: e9 3d 00 d0 ld r9,208(r29)
3480: 2f a9 00 00 cmpdi cr7,r9,0
3484: 41 9e 00 20 beq- cr7,34a4 <.spider_net_xmit+0x368>
3488: 7f a9 f8 00 cmpd cr7,r9,r31
348c: 41 9e 00 18 beq- cr7,34a4 <.spider_net_xmit+0x368>
3490: e9 29 00 00 ld r9,0(r9)
3494: 80 09 00 0c lwz r0,12(r9)
3498: 78 00 40 42 rldicl r0,r0,40,1
349c: 78 00 c0 20 rldicl r0,r0,24,32
34a0: 90 09 00 0c stw r0,12(r9)
34a4: fb fd 00 d0 std r31,208(r29)
34a8: 7c 64 1b 78 mr r4,r3
34ac: 38 7d 00 60 addi r3,r29,96
34b0: 48 00 00 01 bl 34b0 <.spider_net_xmit+0x374>
34b4: 60 00 00 00 nop
34b8: 2f 9c 00 04 cmpwi cr7,r28,4
34bc: 38 60 00 00 li r3,0
34c0: 41 9d 00 b0 bgt- cr7,3570 <.spider_net_xmit+0x434>
34c4: 48 00 00 40 b 3504 <.spider_net_xmit+0x3c8>
34c8: e9 7d 00 58 ld r11,88(r29)
34cc: 81 2a 00 10 lwz r9,16(r10)
34d0: 38 0b 0e 00 addi r0,r11,3584
34d4: 7c 00 04 ac sync
34d8: 91 2b 0e 00 stw r9,3584(r11)
34dc: 39 00 00 01 li r8,1
34e0: 3d 20 80 00 lis r9,-32768
34e4: 99 0d 01 dc stb r8,476(r13)
34e8: 61 29 03 00 ori r9,r9,768
34ec: e9 7d 00 58 ld r11,88(r29)
34f0: 38 0b 0e 04 addi r0,r11,3588
34f4: 7c 00 04 ac sync
34f8: 91 2b 0e 04 stw r9,3588(r11)
34fc: 99 0d 01 dc stb r8,476(r13)
3500: 48 00 00 54 b 3554 <.spider_net_xmit+0x418>
3504: e9 3d 00 58 ld r9,88(r29)
3508: 38 09 0e 04 addi r0,r9,3588
350c: 7c 00 04 ac sync
3510: 80 09 0e 04 lwz r0,3588(r9)
3514: 0c 00 00 00 twi 0,r0,0
3518: 4c 00 01 2c isync
351c: 2f 80 00 00 cmpwi cr7,r0,0
3520: 41 9c 00 34 blt- cr7,3554 <.spider_net_xmit+0x418>
3524: e9 5d 00 70 ld r10,112(r29)
3528: 3d 60 a0 00 lis r11,-24576
352c: e9 2a 00 00 ld r9,0(r10)
3530: 80 09 00 0c lwz r0,12(r9)
3534: 54 00 00 06 rlwinm r0,r0,0,0,3
3538: 7f 80 58 00 cmpw cr7,r0,r11
353c: 41 9e ff 8c beq+ cr7,34c8 <.spider_net_xmit+0x38c>
3540: e8 1d 00 68 ld r0,104(r29)
3544: 7f aa 00 00 cmpd cr7,r10,r0
3548: 41 9e 00 0c beq- cr7,3554 <.spider_net_xmit+0x418>
354c: e9 4a 00 18 ld r10,24(r10)
3550: 4b ff ff dc b 352c <.spider_net_xmit+0x3f0>
3554: e9 3e 80 78 ld r9,-32648(r30)
3558: 38 7d 01 10 addi r3,r29,272
355c: e8 89 00 00 ld r4,0(r9)
3560: 38 84 00 32 addi r4,r4,50
3564: 48 00 00 01 bl 3564 <.spider_net_xmit+0x428>
3568: 60 00 00 00 nop
356c: 38 60 00 00 li r3,0
3570: 38 21 00 b0 addi r1,r1,176
3574: e8 01 00 10 ld r0,16(r1)
3578: eb 21 ff c8 ld r25,-56(r1)
357c: eb 41 ff d0 ld r26,-48(r1)
3580: eb 61 ff d8 ld r27,-40(r1)
3584: eb 81 ff e0 ld r28,-32(r1)
3588: eb a1 ff e8 ld r29,-24(r1)
358c: eb c1 ff f0 ld r30,-16(r1)
3590: eb e1 ff f8 ld r31,-8(r1)
3594: 7c 08 03 a6 mtlr r0
3598: 4e 80 00 20 blr
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