Linux Kernel Debugging Essentials workshop

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Information about Linux Kernel Debugging Essentials workshop

Published on February 19, 2014

Author: LubomirRintel



Slides from Linux Kernel Debugging Essentials workshop at base48 Hackerspace. Not really useful by themselves.

Linux Kernel Debugging Essentials Lubomir Rintel base48 Hackerspace, Brno February 19th , 2014 Kernel Debugging February 19th , 2014 1 / 12

Plan Understanding the way kernel can fail Introduction to infrastructure Obtaining & unserstanding the traces Heplful in-kernel mechanisms Building and trying the replacement code Kernel Debugging February 19th , 2014 2 / 12

Kernel failures Warning, possibly non-fatal: OOPS A fatal error: Panic Usually accompained by a state dump Result of a bug or a hardware failure # echo c >/proc/sysrq-trigger Kernel Debugging February 19th , 2014 3 / 12

Kernel configuration Vanilla kernels Distribution kernels Configuration options (build-time) Runtime configuration (sysctls) Boot time configuration (kernel parameters) Documentation/kernel-parameters.txt Kernel Debugging February 19th , 2014 4 / 12

Lab setup For details & non-Fedora setup, see the hackerspace wiki # yum -y install kernel-debug{,-devel} # debuginfo -y install kernel-debug # yum -y install kexec-tools crash Kernel Debugging February 19th , 2014 5 / 12

Console output Message buffer Screen, UART, USB debugging dongle Early console for boot problems Slowed down output possible Syslog via Netpoll API # dmesg rhgb, quiet console={ttyS*,uart} earlyprintk={vga,serial,dbgp} kernel.printk_delay kernel.printk_ratelimit netconsole.ko g_dbgp.ko Kernel Debugging February 19th , 2014 6 / 12

Reading OOPS messages Processor status Traceback # objdump -lSd {vmlinux,module.ko} # addr2line Kernel Debugging February 19th , 2014 7 / 12

Memory dumps Crash dumps OHCI1394 DMA, can be early too Hypervisor specific dumps We can extract console output from them! crashkernel=auto # systemctl start kdump.service # firescope Kernel Debugging February 19th , 2014 8 / 12

Analyzing dumps crash Kernel Debugging February 19th , 2014 9 / 12

Helpful kernel tools Kernel hacking menu Lockdep detector Hung task detector List corruption detector Stack protector Memory poison CONFIG_DEBUG_* kernel.sysrq kernel.*panic* kernel.prove_locking kernel.hung_task_timeout_secs Kernel Debugging February 19th , 2014 10 / 12

Loading our code into kernel Understand kernel coding Pick a good book Linux Kernel Development, Robert Love, Addison-Wesley: Developer’s Library Understanding the Linux Kernel, Corbet et al., O’Reilly (available online) Try out what do the debugging facilities do! # make -C /lib/modules/$(uname -r)/build SUBDIRS=$PWD modules # insmod module.ko Kernel Debugging February 19th , 2014 11 / 12

Thank you for attending! The source to the slides are embedded in the PDF file. Use pdftk or Acrobat Reader’s ”attachments” to extract them. Kernel Debugging February 19th , 2014 12 / 12

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