** Changed in: linux (Ubuntu Disco)
Status: Confirmed => Won't Fix
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https://bugs.launchpad.net/bugs/1675949
Title:
perf report can't annotate kernel and dbgsym package has wrong
addresses
Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Bionic:
New
Status in linux source package in Cosmic:
New
Status in linux source package in Disco:
Won't Fix
Bug description:
Impact:
Under some condition, 'perf report' is unable to show the assembly
code of a kernel function (perf report -> select a kernel function ->
annotate).
This is not an issue of the kernel itself or the perf tool, instead
it's your environment that is missing the objdump binary (and perf,
unfortunately, doesn't complain about it).
Make sure binutils is not installed, or move away the objdump binary:
# mv /usr/bin/objdump /usr/bin/objdump.foo
Run a perf session and write down all events:
# perf record -a -- sleep 10
# perf report
selct a kernel function, press 'Annotate', a blank screen will appears
(instead of the assembly code).
Now put the objdump binary back (or install binutils):
# mv /usr/bin/objdump.foo /usr/bin/objdump
and run again perf report:
# perf report
select a kernel function, annotate, the disassembly will show up.
Fix:
Make binutils a Depends in SRCPKGNAME-tools-PKGVER-ABINUM - see the
attached patch.
How to test:
Install a patched linux-tools-PKGVER-ABINUM.deb package: it will
require binutils.
Regression:
We are adding a new dependency on a package, so code wise there's no
regression potential - on the other hand, image creation, or
development environment will experience a slight increase in size
(1.8MB on x86-64 and 2.1M on arm64) if they didn't install binutils
already.
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Running zesty 4.10.0-13-generic kernel and running:
$ perf record
followed by
$ perf report
results in output that can't be annotated (even when run as root). The
following message appears:
Couldn't annotate do_io_submit:
No vmlinux file with build id 81ba79d482fa9e3ea58486de8f119b27fe6db55e
was found in the path.
Note that annotation using /proc/kcore requires CAP_SYS_RAWIO
capability.
Please use:
perf buildid-cache -vu vmlinux
Note this is being run as root and /proc/kcore is accessible with dd from the
same shell:
$ dd if=/proc/kcore bs=8 count=16 | hexdump
0000000 457f 464c 0102 0001 0000 0000 0000 0000
0000010 0004 00b7 0001 0000 0000 0000 0000 0000
0000020 0040 0000 0000 0000 0000 0000 0000 0000
0000030 0000 0000 0040 0038 0003 0000 0000 0000
0000040 0004 0000 0000 0000 00e8 0000 0000 0000
Additionally, installing the linux-image-4.10.0-13-generic-dbgsym
actually hurts the situation because the symbol addresses in the
dbgsym don't match the kernel addresses.
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