Debugging APM - cat /proc/apm produces oops

From: Ondrej Zary
Date: Sun Jul 23 2006 - 10:29:38 EST

cat /proc/apm produces oops on my DTK notebook. Using "apm=broken-psr" kernel
parameter fixes that but I lose the battery info. I'd like to have the
battery info (and it works fine in Windows) so I want to debug it and
(hopefully) fix.

The oops:
# cat /proc/apm
<1>BUG: unable to handle kernel paging request at virtual address 00005e88
printing eip:
*pre = 00000000
Oops: 0002 [#4]
Modules linked in:
CPU: 0
EIP: 00c0:[<00002f9d>] Not tainted VLI
EFLAGS: 00010017 (2.6.17-5-dtk #23)
EIP is at 0x2f94
eax: 00000033 ebx: 00000001 ecx: 00000000 edx: 00000000
esi: c10a1000 edi: 00000014 ebp: c4755e8a esp: c4755e88
ds: 00c8 es: 0000 ss: 0068
Process cat (pid: 1928, threadinfo=c4754000 task=c11240b0)
Stack: 5e948001 5fc75e55 00005e94 000000c8 10000033 5ea800c0 00000001 530a0000
00000016 00b86017 00000000 0000530a c010830f 00000060 0000530a 00000033
0000007b 0000007b c0337368 00000000 c10a1000 00000000 00000000 00000282
Call Trace:
<c010830f> apm_bios_call+0x68/0xba <c0108728> apm_get_power_status+0x44/0x90
<c01091a0> apm_get_info+0x34/0xdc <c01617dc> proc_file_read+0xda/0x22d
<c013b5a2> vfs_read+0x82/0x10e <c013b873> sys_read+0x3c/0x62
<c0102397> syscall_call+0x7/0xb
Code: Bad EIP value.
EIP: [<00002f9d>] 0x2f9d SS:ESP 0068:c4755e88

So it looks like it dies somewhere in the APM BIOS code. But how to find
exactly where and/or why? Maybe use GDB somehow (I've used it only for really
simple debugging yet).
I've tried calling the APM 0x530A function from DOS (real mode, int 15h) and
single-stepping the BIOS APM code (using good old user-friendly Turbo
Debugger). Noticed some OUTs to 0xB1 (or something like that), then some PCI
accesses (0xCF8 and 0xCFC) and then IP ended in area of all zeros. When I
step over the int 15h call, it works fine - returns correct info.

Ondrej Zary
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