/usr/lib/radare/bin/flag-kallsyms is in radare-common 1:1.5.2-6.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 | #!/bin/sh
# only for linux
#
cat /proc/kallsyms | awk '{print "f "$3" @ 0x"$1}'
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