Hi Maciej,
> > I suspect 63:32 are the critical bits of the upper 96 bits since SD/LD
> > is sufficient. Summery of observations thus far: save/restore works with
> > SQ/LQ and SD/LD, but not SW/LW, in a 32-bit kernel ceteris paribus.
>
> This does look intriguing.
I believe the simple answer to this mystery is that addresses are not
supposed to be sign-extended, given the look of $31 below. What are
your thoughts on this?
To delay and recover from the trap I chose printk_delay_msec as an
(arbitrary) trigger with "echo 1 >/proc/sys/kernel/printk_delay".
.macro check_reg reg
.extern printk_delay_msec
sll $27, \reg, 0
beq $27, \reg, 1f
nop
lw $27, printk_delay_msec
beq $27, $0, 1f
nop
.set at=$27
sw $0, printk_delay_msec
.set noat
break 12
nop
1:
.endm
Break instruction in kernel code[#1]:
CPU: 0 PID: 94 Comm: echo Not tainted 4.12.0+ #510
task: 81fb5500 task.stack: 81f70000
$ 0 :
0000000000000000
0000000000000020
ffffffff8100a874
ffffffff800beeb0
$ 4 :
ffffffffffffffff
000000000fb60000
000000000082cb49
0000000000000001
$ 8 :
0000000000000875
ffffffff80260684
ffffffff80539f0c
ffffffffffffff80
$12 :
000000007f9582e0
0000000077f1a2d0
0000000000000000
0000000000000000
$16 :
ffffffff81500d80
ffffffff81020be0
ffffffff81f71dd8
000000000fb79000
$20 :
ffffffff805150c0
000000000fb61000
ffffffff814e59f8
000000000fb60000
$24 :
0000000000000000
0000000077e4d67c
$28 :
ffffffff81f70000
ffffffff81f71bf8
ffffffff815010f8
00000000800bed80
Hi : 00000000
Lo : 00000048
epc : 800beeb0 unmap_page_range+0x3cc/0x664
ra : 00000000800bed80 unmap_page_range+0x29c/0x664
Status: 30018c03 KERNEL EXL IE
Cause : 50000424 (ExcCode 09)
PrId : 00002e42 (R5900)
Modules linked in:
Process echo (pid: 94, threadinfo=81f70000, task=81fb5500, tls=00adc0e0)
Stack : 8053a2e8 00000000 00000001 00000000 00000000 80520000 00000000 30018c01
00000000 00000000 001fffff 80525f60 8100a874 ffffffff ffffffff ffffffff
ffffffff ffffffff 0fb60000 00000000 0082cb49 00000000 00000001 00000000
01000200 8025bfcc 014200ca 00000001 81f71c68 81f71c68 00000001 00000000
00000002 81f71cb0 81f71d10 8025c010 00000000 30018c01 8053a2e8 00000000
...
Call Trace:
[<800beeb0>] unmap_page_range+0x3cc/0x664
[<8025bfcc>] simple_strtoull+0x34/0x68
[<8025c010>] simple_strtoul+0x10/0x1c
Code: 1220ff6b ae440008 8e220014 <30430001> 2442ffff 0223100a 8c420004 30420001 14400013
---[ end trace e89f1298cab4fd73 ]---
Fixing recursive fault but reboot is needed!
Fredrik
