Книга: Embedded Linux Primer: A Practical, Real-World Approach
14.5.3. KGDB on Panic
14.5.3. KGDB on Panic
If KGDB is enabled, the kernel attempts to pass control back to KGDB upon error exceptions. In some cases, the error itself will be readily apparent. To use this feature, a connection must already be established between KGDB and gdb. When the exception condition occurs, KGDB emits a Stop Reply packet to gdb, indicating the reason for the trap into the debug handler, as well as the address where the trap condition occurred. Listing 14-24 illustrates the sequence.
Listing 14-24. Trapping Crash on Panic Using KGDB
$ ppc-_4xx-gdb --silent vmlinux
(gdb) target remote /dev/ttyS0
Remote debugging using /dev/ttyS0
Malformed response to offset query, qOffsets
(gdb) target remote /dev/ttyS0
Remote debugging using /dev/ttyS0
breakinst () at arch/ppc/kernel/ppc-stub.c:825
825 }
(gdb) c
Continuing.
<< KGDB gains control from panic() on crash >>
Program received signal SIGSEGV, Segmentation fault.
0xc0215d6c in pcibios_init () at arch/ppc/kernel/pci.c:1263
1263 *(int *)-1 = 0;
(gdb) bt
#0 0xc0215d6c in pcibios_init () at arch/ppc/kernel/pci.c:1263
#1 0xc020e728 in do_initcalls () at init/main.c:563
#2 0xc020e7c4 in do_basic_setup () at init/main.c:605
#3 0xc0001374 in init (unused=0x20) at init/main.c:677
#4 0xc00049d0 in kernel_thread ()
Previous frame inner to this frame (corrupt stack?)
(gdb)
The crash in this example was contrived by a simple write to an invalid memory location (all ones). We first establish a connection from gdb to KGDB and allow the kernel to continue to boot. Notice that we didn't even bother to set breakpoints. When the crash occurs, we see the line of offending code and get a nice backtrace to help us determine its cause.
Оглавление книги
- 14.2. Using KGDB for Kernel Debugging
- 14.2.1. KGDB Kernel Configuration
- 14.2.2. Target Boot with KGDB Support
- Отладчик kgdb
- Проблема 4. Ошибка kernel panic - not syncing
- Проблема 3. Ошибка kernel panic: VFS: Unable to mount root fs
- 14.5. When It Doesn't Boot
- 14.2.3. Useful Kernel Breakpoints
- 14.5.2. Dumping the printk Log Buffer