A: Please install debuginfo for the kernel that was running and provide the following output

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# gdb /usr/lib/debug/usr/lib/modules/<yourkernel>/kernel/drivers/net/ethernet/intel/i40e/i40e.ko.debug
(gdb) list *i40e_xmit_frame_ring+0x5667

But for buildin functions which don’t have .ko.debug file, just use vmlinux file, e.g.

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# gdb /usr/lib/debug/lib/modules/<yourkernel>/vmlinux
(gdb) list *icmp_rcv+0x193/0x3b0

Q: how to print pr_debug info

A: Usually you should able to print it when DEBUG defined. just echo 8 > /proc/sys/kernel/printk should be enough. See printk for more info.

Q: Dynamic debug

A: When your kernel has config “CONFIG_DYNAMIC_DEBUG=y”, pr_debug will not print anything by default. You need to use /sys/kernel/debug/dynamic_debug/control to control the pr_debug info.

cat /sys/kernel/debug/dynamic_debug/control could show all the dynamic debug lines. The control format looks like "file:line [module]function flags format" e.g.

  1. Open file’s dynamic debug
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echo 'file net/ipv4/ping.c +p' > /sys/kernel/debug/dynamic_debug/control
  • “+” add the given flags
  • “-” remove the given flags
  • “=” set the flags to the given flags
  • p enables the pr_debug() callsite.
  • f Include the function name in the printed message
  • l Include line number in the printed message
  • m Include module name in the printed message
  • t Include thread ID in messages not generated from interrupt context
  • _ No flags are set. (Or’d with others on input)
  1. Enable module’s dynamic debuginfo
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echo 'module bonding +p' > /sys/kernel/debug/dynamic_debug/control
  1. Use line number
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/* enable line 12 debug */
echo 'file kxtj2 line 12 +p' > /sys/kernel/debug/dynamic_debug/control
echo 'module akm line 12 +p' > /sys/kernel/debug/dynamic_debug/control
/* enable line 12-230 debug */
echo 'file kxtj2 line 12-230 +p' > /sys/kernel/debug/dynamic_debug/control
echo 'module akm line 12-230 +p' > /sys/kernel/debug/dynamic_debug/control
/* enable line 12 to the end */
echo 'file kxtj2 line 12- +p' > /sys/kernel/debug/dynamic_debug/control
echo 'module akm line 12- +p' > /sys/kernel/debug/dynamic_debug/control
/* starts from begining to line 230 */
echo 'file kxtj2 line -230 +p' > /sys/kernel/debug/dynamic_debug/control
echo 'module akm line -230 +p' > /sys/kernel/debug/dynamic_debug/control
  1. enable function debugs
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echo 'file kxtj2 func kxtj2_probe +p' > /sys/kernel/debug/dynamic_debug/control
echo 'module akm func init +p' > /sys/kernel/debug/dynamic_debug/control

For more usage info, see Dynamic debug.