linux-kernel - Issue using faddr2line on kernel modules

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Message-ID: <CAPDLWs_iSrbXwfKa6CQ0f6H6GE4U88uRhaFgabRjMmSuSEpsiA@mail.gmail.com>
Date:   Mon, 17 Jan 2022 10:27:14 +0530
From:   Kaiwan N Billimoria <kaiwan.billimoria@...il.com>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        jpoimboe@...hat.com
Cc:     Chi-Thanh Hoang <chithanh.hoang@...il.com>
Subject: Issue using faddr2line on kernel modules

Hi there,

Am researching using the cool faddr2line script to help debug Oops'es
from kernel modules..
I find it works just fine when used against the unstripped vmlinux
with debug symbols.

My use case is for a kernel module which Oopses, though. Here's my scenario:
I built a module on a custom debug kernel (5.10.60) with most debug
options enabled...
KASLR is enabled by default as well.

A test kernel module Oopses on my x86_64 guest running this kernel with:
RIP: 0010:do_the_work+0x15b/0x174 [oops_tryv2]

So, i try this:

$ <...>/linux-5.10.60/scripts/faddr2line ./oops_tryv2.ko do_the_work+0x15b/0x174
bad symbol size: base: 0x0000000000000000 end: 0x0000000000000000
$

(It works fine with addr2line though!).
Now I think I've traced the faddr2line script's failure to locate
anything down to this:
...
done < <(${NM} -n $objfile | awk -v fn=$func -v end=$file_end '$3 ==
fn { found=1; line    =$0; start=$1; next } found == 1 { found=0;
print line, "0x"$1 } END {if (found == 1) print     line, end; }')

The nm output is:
$ nm -n ./oops_tryv2.ko |grep -i do_the_work
0000000000000000 t do_the_work
$

nm shows the text addr as 0x0; this is obviously incorrect (same 0x0
with objdump -d on the module).
Am I missing something? Any suggestions as to what I can try, to get
faddr2line working?

TIA,
Regards,
Kaiwan.