debuging kernel doesn't start: invalid `Elf' handle

[Nudin]

I followed the install-guide. After that I started it via sudo drgn -k and got:

Traceback (most recent call last):
  File "/usr/bin/drgn", line 11, in <module>
    load_entry_point('drgn==0.0.1', 'console_scripts', 'drgn')()
  File "/usr/lib/python3.7/site-packages/drgn-0.0.1-py3.7-linux-x86_64.egg/drgn/internal/cli.py", line 90, in main
    prog.load_default_debug_info()
_drgn.FileFormatError: libelf error: invalid `Elf' handle

Any idea what I'm doing wrong?

[osandov]

Could you provide the output of running sudo strace drgn -k? Hopefully I can figure out which file failed from that.

Some other general information that would be appreciated:

• What distro and distro version is this on?
• What version of elftutils do you have installed? eu-readelf --version should give you that unless you did anything special to get the elfutils libraries.

[Nudin]

• Arch Linux
• eu-readelf (elfutils) 0.176
• strace: https://gist.github.com/Nudin/37459465d89db7ef21dc1f217519d752

[osandov]

Ah, it looks like you're trying to debug the official Arch kernel, but Arch doesn't ship debugging information. Unfortunately, the only way to get debugging information on Arch is to build the kernel yourself with CONFIG_DEBUG_INFO=y. However, drgn should definitely be giving you a better error message here. I can reproduce the issue here, so I'll fix that.

[Nudin]

Makes total sense! Adding a proper error message sounds the right way! Thanks for the quick help.

[osandov]

This is fixed by the larger rework in 423d2cd:

$ sudo drgn -k
could not get debugging information for:
/usr/lib/modules/5.3.1-arch1-1-ARCH/kernel/drivers/input/serio/serio.ko.xz (libdwfl error: No DWARF information found)
/usr/lib/modules/5.3.1-arch1-1-ARCH/kernel/drivers/input/serio/i8042.ko.xz (libdwfl error: No DWARF information found)
/usr/lib/modules/5.3.1-arch1-1-ARCH/kernel/drivers/net/net_failover.ko.xz (libdwfl error: No DWARF information found)
/usr/lib/modules/5.3.1-arch1-1-ARCH/kernel/drivers/net/virtio_net.ko.xz (libdwfl error: No DWARF information found)
/usr/lib/modules/5.3.1-arch1-1-ARCH/kernel/drivers/macintosh/mac_hid.ko.xz (libdwfl error: No DWARF information found)
... 40 more

Thanks for reporting this!