Bug 201551

Summary:	perf no longer resolves module symbols
Product:	Tracing/Profiling	Reporter:	Souvik Banerjee (souvik1997)
Component:	Perf tool	Assignee:	Arnaldo Carvalho de Melo (acme)
Status:	NEW ---
Severity:	normal	CC:	jolsa
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	4.19	Subsystem:
Regression:	Yes	Bisected commit-id:

Description Souvik Banerjee 2018-10-29 02:40:44 UTC

I am using perf to record both kernel and user data. This worked with perf 4.18. With perf 4.19, I noticed that kernel module symbols were no longer being resolved. They appear as [unknown] in `perf report` and have a hexadecimal address. The modules I am interested in are ext4 and xfs, but I've noticed this happening for every module.


I bisected this bug to the following commit: 

commit edeb0c90df3581b821a764052d185df985f8b8dc
Author: Arnaldo Carvalho de Melo <acme@redhat.com>
Date:   Tue Oct 16 17:08:29 2018 -0300

    perf tools: Stop fallbacking to kallsyms for vdso symbols lookup

Comment 1 Arnaldo Carvalho de Melo 2018-10-29 18:02:56 UTC

Can you try with 'perf script' to see if the backtraces are ok? I've reproduced the problem with 'perf report --stdio' and I'm debugging this now.

Comment 2 Souvik Banerjee 2018-10-30 02:43:21 UTC

It looks like `perf script` is ok. It's able to resolve addresses to symbols+offsets.

The command I am using is:

perf record --all-kernel -g --call-graph dwarf [workload]