[Crash-utility] Why module's global symbol cannot be displayed in crash? [ARM]
Lei Wen
adrian.wenl at gmail.com
Sun Mar 24 09:02:00 UTC 2013
Dave,
On Fri, Mar 22, 2013 at 9:51 PM, Dave Anderson <anderson at redhat.com> wrote:
>
>
> ----- 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.
The $a/$d symbol actually be added into module symbol list in checking
mod_ext_symtable in store_load_module_symbols().
While store_load_module_symbols use verify_symbol() to check the
symbol in the minisyms. It didn't check in the mod_ext_symtable stage.
I get rid of this by below patch, how do you think for it?
diff --git a/symbols.c b/symbols.c
index 2ae0dbd..b707f3e 100755
--- a/symbols.c
+++ b/symbols.c
@@ -10594,7 +10594,8 @@ store_load_module_symbols(bfd *bfd, int
dynamic, void *minisyms,
break;
}
}
- if (!found) {
+ if (!found && machdep->verify_symbol(spx->name,
+ spx->value, spx->type)) {
if (CRASHDEBUG(2))
fprintf(fp, "append ext %s (%lx)\n",
spx->name, spx->value);
Thanks,
Lei
>
> 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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