[Crash-utility] Why module's global symbol cannot be displayed in crash? [ARM]
Dave Anderson
anderson at redhat.com
Fri Mar 22 13:51:39 UTC 2013
----- Original Message -----
> On Thu, Mar 21, 2013 at 03:02:54PM -0400, Dave Anderson wrote:
> > If for some reason you can't get them, I can make them available to
> > you.
> > And Lei Wen can also give you a sample dumpfile from his
> > environment.
>
> Got them from Luc.
>
> > > Are you able to access module symbols on ARM dump (the one that Luc provided)?
> > > Or is it failing completely?
> >
> > I *think* so...
> >
> > This module text disassembly looks right:
> >
> > crash> dis usbnet_suspend
> > 0xbf000ae8 <usbnet_suspend>: push {r3, r4, r5, lr}
> > 0xbf000aec <usbnet_suspend+4>: add r0, r0, #32
> > 0xbf000af0 <usbnet_suspend+8>: mov r5, r1
> > 0xbf000af4 <usbnet_suspend+12>: bl 0xc01b8264
> > <dev_get_drvdata>
> > 0xbf000af8 <usbnet_suspend+16>: ldrb r3, [r0, #36] ; 0x24
> > 0xbf000afc <usbnet_suspend+20>: mov r4, r0
> > 0xbf000b00 <usbnet_suspend+24>: add r2, r3, #1
> > 0xbf000b04 <usbnet_suspend+28>: cmp r3, #0
> > 0xbf000b08 <usbnet_suspend+32>: strb r2, [r0, #36] ; 0x24
> > 0xbf000b0c <usbnet_suspend+36>: bne 0xbf000bdc
> > <usbnet_suspend+244>
> > 0xbf000b10 <usbnet_suspend+40>: mrs r3, CPSR
> > 0xbf000b14 <usbnet_suspend+44>: orr r3, r3, #128 ; 0x80
> > 0xbf000b18 <usbnet_suspend+48>: msr CPSR_c, r3
> > 0xbf000b1c <usbnet_suspend+52>: mov r0, #1
> > 0xbf000b20 <usbnet_suspend+56>: bl 0xc0015f40
> > <add_preempt_count>
> > 0xbf000b24 <usbnet_suspend+60>: ldr r3, [r4, #200] ; 0xc8
> > 0xbf000b28 <usbnet_suspend+64>: cmp r3, #0
> > 0xbf000b2c <usbnet_suspend+68>: beq 0xbf000b70
> > <usbnet_suspend+136>
> > 0xbf000b30 <usbnet_suspend+72>: tst r5, #1024 ; 0x400
> > 0xbf000b34 <usbnet_suspend+76>: beq 0xbf000b70
> > <usbnet_suspend+136>
> > 0xbf000b38 <usbnet_suspend+80>: mrs r3, CPSR
> > ...
> >
> > This (r) data looks OK:
> >
> > crash> p smsc95xx_netdev_ops
> > smsc95xx_netdev_ops = $8 = {
> > ndo_init = 0,
> > ndo_uninit = 0,
> > ndo_open = 0xbf000514 <usbnet_open>,
> > ndo_stop = 0xbf000bec <usbnet_stop>,
> > ndo_start_xmit = 0xbf001a60 <usbnet_start_xmit>,
> > ndo_select_queue = 0,
> > ndo_change_rx_flags = 0,
> > ndo_set_rx_mode = 0,
> > ndo_set_multicast_list = 0xbf008abc <smsc95xx_set_multicast>,
> > ndo_set_mac_address = 0xc025d854 <eth_mac_addr>,
> > ndo_validate_addr = 0xc025d6f8 <eth_validate_addr>,
> > ndo_do_ioctl = 0xbf00926c <smsc95xx_ioctl>,
> > ndo_set_config = 0,
> > ndo_change_mtu = 0xbf000de0 <usbnet_change_mtu>,
> > ndo_neigh_setup = 0,
> > ndo_tx_timeout = 0xbf000d4c <usbnet_tx_timeout>,
> > ndo_get_stats64 = 0,
> > ndo_get_stats = 0,
> > ndo_vlan_rx_add_vid = 0,
> > ndo_vlan_rx_kill_vid = 0,
> > ndo_set_vf_mac = 0,
> > ndo_set_vf_vlan = 0,
> > ndo_set_vf_tx_rate = 0,
> > ndo_get_vf_config = 0,
> > ndo_set_vf_port = 0,
> > ndo_get_vf_port = 0,
> > ndo_setup_tc = 0,
> > ndo_add_slave = 0,
> > ndo_del_slave = 0,
> > ndo_fix_features = 0,
> > crash>
>
> I'm able to see the same.
>
> Setting suitable debug level reveals:
>
> bf00f040 (bf00f000): scsi_wait_scan syms: 0 gplsyms: 0 ksyms: 1
> bf00a1f8 (bf008000): smsc95xx syms: 0 gplsyms: 0 ksyms: 60
> bf002a40 (bf000000): usbnet syms: 0 gplsyms: 24 ksyms: 65
>
> The ksyms comes from KALLSYMS and by default it only includes text and
> inittext symbols. This explains why Lei is not able to see data etc. symbols
> when he runs 'sym -m <module>'.
>
> So I believe crash on ARM works as it should in this case.
I note that the symbols exported by ARM modules prior to mod -[sS]
contains a bunch of "$d" and "$a" symbols. The ARM arm_verify_symbol()
function rejects symbols of that type, but that is only called if the
"mod -[sS]" function is run.
In other words, this is the flow during session initialization:
module_init()
store_module_symbols_v2() -> symbols from KALLSYMS + in-kernel module struct
And if "mod -[sS]" is done, it goes like this:
cmd_mod()
do_module_cmd()
load_module_symbols()
store_load_module_symbols() -> symbols from module.ko file
machdep->verify_symbol()
So the "$d" and "$a" are there from the initialization-time onward.
But since store_module_symbols_v2() has never called machdep->verify_symbol()
I'm a bit hesitant to make it do so for all architectures without knowing the
consequences. But it certainly seems legitimate in the "machine_type("ARM")" case.
> > But the user-space vtop is clearly wrong:
> >
> > crash> vm
> > PID: 1495 TASK: c1ef1380 CPU: 0 COMMAND: "bash"
> > MM PGD RSS TOTAL_VM
> > c30cd1e0 c1de4000 1484k 2940k
> > VMA START END FLAGS FILE
> > c1e9ae90 8000 c2000 8001875 /bin/bash
> > c1e9aee8 c9000 ce000 8101877 /bin/bash
> > c1e9af40 ce000 d3000 100077
> > c2fc27b0 1247000 1268000 100077
> > c2fc2650 4001c000 4001d000 100077
> > c1e9af98 40038000 40055000 8000875 /lib/ld-linux.so.3
> > c2fc20d0 4005c000 4005d000 8100875 /lib/ld-linux.so.3
> > c2fc2758 4005d000 4005e000 8100877 /lib/ld-linux.so.3
> > ...
> >
> >
> > crash> vtop 8000
> > VIRTUAL PHYSICAL
> > 8000 8000
> >
> > PAGE DIRECTORY: c1de4000
> > PGD: c1de4000 => 412
> > PMD: c1de4000 => 412
> > PAGE: 0 (1MB)
> >
> >
> > VMA START END FLAGS FILE
> > c1e9ae90 8000 c2000 8001875 /bin/bash
> >
> > crash> vtop 4005d000
> > VIRTUAL PHYSICAL
> > 4005d000 4005d000
> >
> > PAGE DIRECTORY: c1de4000
> > PGD: c1de5000 => 40000412
> > PMD: c1de5000 => 40000412
> > PAGE: 40000000 (1MB)
> >
> >
> > VMA START END FLAGS FILE
> > c2fc2758 4005d000 4005e000 8100877 /lib/ld-linux.so.3
>
> This is actually a known issue on ARM (just remembered that). When the crash
> happens it identity maps the whole address space of the running process. This
> has been fixed by upstream commit:
>
> commit 2c8951ab0c337cb198236df07ad55f9dd4892c26
> Author: Will Deacon <will.deacon at arm.com>
> Date: Wed Jun 8 15:53:34 2011 +0100
>
> ARM: idmap: use idmap_pgd when setting up mm for reboot
>
> For soft-rebooting a system, it is necessary to map the MMU-off code
> with an identity mapping so that execution can continue safely once the
> MMU has been switched off.
>
> Currently, switch_mm_for_reboot takes out a 1:1 mapping from 0x0 to
> TASK_SIZE during reboot in the hope that the reset code lives at a
> physical address corresponding to a userspace virtual address.
>
> This patch modifies the code so that we switch to the idmap_pgd tables,
> which contain a 1:1 mapping of the cpu_reset code. This has the
> advantage of only remapping the code that we need and also means we
> don't need to worry about allocating a pgd from an atomic context in the
> case that the physical address of the cpu_reset code aliases with the
> virtual space used by the kernel.
>
> It went in for 3.2 and Luc's kernel is v3.1.1 which explains this.
>
> If you select any other task vtop should work fine. For example cron daemon:
>
> crash> vm
> PID: 316 TASK: c2a7c160 CPU: 0 COMMAND: "crond"
> MM PGD RSS TOTAL_VM
> c30cd060 c0a70000 836k 2916k
> VMA START END FLAGS FILE
> c1cdd860 8000 15000 8001875 /usr/sbin/crond
> c1cddcd8 1c000 1d000 8101875 /usr/sbin/crond
> c1d7d758 1d000 1e000 8101877 /usr/sbin/crond
> c1cddd88 1e000 9e000 100077
> c1d7d5a0 9a4000 9c5000 100077
> ...
>
> crash> vtop 8000
> VIRTUAL PHYSICAL
> 8000 c1030000
>
> PAGE DIRECTORY: c0a70000
> PGD: c0a70000 => c2b3d831
> PMD: c0a70000 => c2b3d831
> PTE: c2b3d020 => c103018f
>
> PAGE: c1030000
>
> PTE PHYSICAL FLAGS
> c103018f c1030000 (PRESENT|YOUNG|EXEC)
>
> VMA START END FLAGS FILE
> c1cdd860 8000 15000 8001875 /usr/sbin/crond
>
> PAGE PHYSICAL MAPPING INDEX CNT FLAGS
> c047d600 c1030000 c09b1590 0 2 228
>
OK good, that explains that...
Is it something that can be worked-around, or is the original pgd
lost forever? If it is not recoverable, then maybe the user-space
vtop should recognize that the bait-and-switch has occurred and fail?
Your call...
Thanks,
Dave
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