run uml in gdb

就先build uml..是follow : http://user-mode-linux.sourceforge.net/source.html
大概是：
所有make command (make defconfig, make menuconfig, make) 都要加上 ARCH=um
kernel config 要開啟 kernel-hacking : Compile with debug info 和 compile with frame-buffer-support (default也是開啟的)

然後 build rootfs，這部份 follow 一般用 busybox 產生 rootfs 的 instruction就可以。
我是用上一篇，kgdb 的 busybox.

用 gdb run uml linux. 重點是：

• linux 的 rootfs 需要用 gdb -x command 的方式，讓 gdb 把 rootfs parameter 傳給 linux
• uml linux 會產生 SIGSEGV signal ，要請 gdb bypass -- 這個也一樣放到 -x command 的 command script 中

command 這個檔的內容：

set args ubd0=/home/charles-chang/uml/linux-2.6.34.1/busybox.img

handle SIGUSR1 pass nostop noprint

handle SIGSEGV pass nostop noprint

gdb 啟動後，可以先設break pont 到 start_kernel break start_kernel 然後就可以開始 run: run 然後就會停在 start_kernel。用 continue 繼續...然後會停在一個signal 的地方...再用 continue 繼續就可以...

這個就是 gdb log: charles-chang@rbtlegacy:~/uml/linux-2.6.34.1$ gdb -x ./command ./linux GNU gdb 6.8-debian Copyright (C) 2008 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "i486-linux-gnu"... (gdb) run Starting program: /home/charles-chang/uml/linux-2.6.34.1/linux ubd0=/home/charles-chang/uml/linux-2.6.34.1/busybox.img Locating the bottom of the address space ... 0x1000 Locating the top of the address space ... 0xc0000000 Core dump limits : soft - 0 hard - NONE Checking that ptrace can change system call numbers...OK Checking syscall emulation patch for ptrace...OK Checking advanced syscall emulation patch for ptrace...OK Checking for tmpfs mount on /dev/shm...OK Checking PROT_EXEC mmap in /dev/shm/...OK Checking for the skas3 patch in the host: - /proc/mm...not found: No such file or directory - PTRACE_FAULTINFO...not found - PTRACE_LDT...not found UML running in SKAS0 mode Linux version 2.6.34.1 (charles-chang@rbtlegacy) (gcc version 4.3.2 (Debian 4.3.2-1.1) ) #1 Mon Jul 26 15:42:19 CST 2010 Built 1 zonelists in Zone order, mobility grouping on. Total pages: 8128 Kernel command line: ubd0=/home/charles-chang/uml/linux-2.6.34.1/busybox.img root=98:0 PID hash table entries: 128 (order: -3, 512 bytes) Dentry cache hash table entries: 4096 (order: 2, 16384 bytes) Inode-cache hash table entries: 2048 (order: 1, 8192 bytes) Memory: 30048k available Hierarchical RCU implementation. RCU-based detection of stalled CPUs is enabled. NR_IRQS:15 Calibrating delay loop... 1900.54 BogoMIPS (lpj=9502720) Mount-cache hash table entries: 512 Checking for host processor cmov support...Yes Checking that host ptys support output SIGIO...Yes Checking that host ptys support SIGIO on close...No, enabling workaround Using 2.6 host AIO NET: Registered protocol family 16 bio: create slab at 0 Switching to clocksource itimer NET: Registered protocol family 2 IP route cache hash table entries: 1024 (order: 0, 4096 bytes) TCP established hash table entries: 1024 (order: 1, 8192 bytes) TCP bind hash table entries: 1024 (order: 0, 4096 bytes) TCP: Hash tables configured (established 1024 bind 1024) TCP reno registered UDP hash table entries: 256 (order: 0, 4096 bytes) UDP-Lite hash table entries: 256 (order: 0, 4096 bytes) NET: Registered protocol family 1 IRQ 9/mconsole: IRQF_DISABLED is not guaranteed on shared IRQs mconsole (version 2) initialized on /home/charles-chang/.uml/oJVcbD/mconsole Checking host MADV_REMOVE support...OK Host TLS support detected Detected host type: i386 (GDT indexes 6 to 9) VFS: Disk quotas dquot_6.5.2 Dquot-cache hash table entries: 1024 (order 0, 4096 bytes) msgmni has been set to 58 io scheduler noop registered io scheduler deadline registered io scheduler cfq registered (default) TCP cubic registered NET: Registered protocol family 17 Initialized stdio console driver Console initialized on /dev/tty0 console [tty0] enabled Initializing software serial port version 1 console [mc-1] enabled ubda: unknown partition table IRQ 3/console-write: IRQF_DISABLED is not guaranteed on shared IRQs IRQ 2/console: IRQF_DISABLED is not guaranteed on shared IRQs IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs kjournald starting. Commit interval 5 seconds EXT3-fs (ubda): mounted filesystem with writeback data mode VFS: Mounted root (ext3 filesystem) readonly on device 98:0. line_ioctl: tty0: unknown ioctl: 0x5600 [New LWP 32568] Executing new program: /proc/32568/exe /proc/32568/exe: Permission denied. (gdb) run The program being debugged has been started already. Start it from the beginning? (y or n) n Program not restarted. (gdb) c Continuing. IRQ 13/xterm: IRQF_DISABLED is not guaranteed on shared IRQs Processing /etc/profile... Done # INFO: RCU detected CPU 0 stall (t=2009 jiffies) IRQ 2/console: IRQF_DISABLED is not guaranteed on shared IRQs IRQ 3/console-write: IRQF_DISABLED is not guaranteed on shared IRQs IRQ 10/winch: IRQF_DISABLED is not guaranteed on shared IRQs INFO: RCU detected CPU 0 stall (t=1715 jiffies)

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另外這一頁 http://user-mode-linux.sourceforge.net/old/debugging.html 有 configure uml kernel 另一種 mode 配合 gdb debug...下次試試.

原來這一篇 http://web2.clarkson.edu/class/cs644/kernel/setup/uml/gdb_uml.html 就有講在 gdb 下用 command 指定 root image 的方法...
# gdb ./linux (gdb) handle SIGSEGV pass nostop noprint Signal Stop Print Pass to program Description SIGSEGV No No Yes Segmentation fault (gdb) handle SIGUSR1 pass nostop noprint Signal Stop Print Pass to program Description SIGUSR1 No No Yes User defined signal 1 (gdb) r ubd0=/home/charles-chang/uml/linux-2.6.34.1/busybox.img 這一篇有exmple : 教你怎麼trace do_fork..