The old kernel 3.4 has no "flag" field in /dev/kmsg.

The format was documented in 3.5: 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/dev-kmsg?h=v3.5

A sample output:
6,563,2459423;asoc: sitar_rx1 <-> msm-dai-q6.16384 mapping ok
4,564,2459484;sitar_codec sitar_codec: ASoC: Failed to create Digital 
Mic1 debugfs file
6,565,2460674;asoc: sitar_tx1 <-> msm-dai-q6.16385 mapping ok

In logbookd parsing expects 4 initial fields, so the ';' sign is skipped 
at line main.c:338 and while loop at line 352 rolls out of the buffer 
into infinity causing segmentation fault.

(I'm playing with running PostmarketOS on Jolla phone and I'm stuck here 
with downstream 3.4 kernel)