Re: [Crash-utility] Why module's global symbol cannot be displayed in crash? [ARM]

Dave, On Fri, Mar 22, 2013 at 9:51 PM, Dave Anderson <anderson(a)redhat.com&gt; 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(a)arm.com&gt; >> 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 > > > > -- > Crash-utility mailing list > Crash-utility(a)redhat.com > https://www.redhat.com/mailman/listinfo/crash-utility -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility