3c78f5d81a
The correct name is CONFIG_DEBUG_FS, add the missing underscore. Signed-off-by: Marton Nemeth <nm127@freemail.hu> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
254 lines
7.5 KiB
Plaintext
254 lines
7.5 KiB
Plaintext
Using gcov with the Linux kernel
|
|
================================
|
|
|
|
1. Introduction
|
|
2. Preparation
|
|
3. Customization
|
|
4. Files
|
|
5. Modules
|
|
6. Separated build and test machines
|
|
7. Troubleshooting
|
|
Appendix A: sample script: gather_on_build.sh
|
|
Appendix B: sample script: gather_on_test.sh
|
|
|
|
|
|
1. Introduction
|
|
===============
|
|
|
|
gcov profiling kernel support enables the use of GCC's coverage testing
|
|
tool gcov [1] with the Linux kernel. Coverage data of a running kernel
|
|
is exported in gcov-compatible format via the "gcov" debugfs directory.
|
|
To get coverage data for a specific file, change to the kernel build
|
|
directory and use gcov with the -o option as follows (requires root):
|
|
|
|
# cd /tmp/linux-out
|
|
# gcov -o /sys/kernel/debug/gcov/tmp/linux-out/kernel spinlock.c
|
|
|
|
This will create source code files annotated with execution counts
|
|
in the current directory. In addition, graphical gcov front-ends such
|
|
as lcov [2] can be used to automate the process of collecting data
|
|
for the entire kernel and provide coverage overviews in HTML format.
|
|
|
|
Possible uses:
|
|
|
|
* debugging (has this line been reached at all?)
|
|
* test improvement (how do I change my test to cover these lines?)
|
|
* minimizing kernel configurations (do I need this option if the
|
|
associated code is never run?)
|
|
|
|
--
|
|
|
|
[1] http://gcc.gnu.org/onlinedocs/gcc/Gcov.html
|
|
[2] http://ltp.sourceforge.net/coverage/lcov.php
|
|
|
|
|
|
2. Preparation
|
|
==============
|
|
|
|
Configure the kernel with:
|
|
|
|
CONFIG_DEBUG_FS=y
|
|
CONFIG_GCOV_KERNEL=y
|
|
|
|
and to get coverage data for the entire kernel:
|
|
|
|
CONFIG_GCOV_PROFILE_ALL=y
|
|
|
|
Note that kernels compiled with profiling flags will be significantly
|
|
larger and run slower. Also CONFIG_GCOV_PROFILE_ALL may not be supported
|
|
on all architectures.
|
|
|
|
Profiling data will only become accessible once debugfs has been
|
|
mounted:
|
|
|
|
mount -t debugfs none /sys/kernel/debug
|
|
|
|
|
|
3. Customization
|
|
================
|
|
|
|
To enable profiling for specific files or directories, add a line
|
|
similar to the following to the respective kernel Makefile:
|
|
|
|
For a single file (e.g. main.o):
|
|
GCOV_PROFILE_main.o := y
|
|
|
|
For all files in one directory:
|
|
GCOV_PROFILE := y
|
|
|
|
To exclude files from being profiled even when CONFIG_GCOV_PROFILE_ALL
|
|
is specified, use:
|
|
|
|
GCOV_PROFILE_main.o := n
|
|
and:
|
|
GCOV_PROFILE := n
|
|
|
|
Only files which are linked to the main kernel image or are compiled as
|
|
kernel modules are supported by this mechanism.
|
|
|
|
|
|
4. Files
|
|
========
|
|
|
|
The gcov kernel support creates the following files in debugfs:
|
|
|
|
/sys/kernel/debug/gcov
|
|
Parent directory for all gcov-related files.
|
|
|
|
/sys/kernel/debug/gcov/reset
|
|
Global reset file: resets all coverage data to zero when
|
|
written to.
|
|
|
|
/sys/kernel/debug/gcov/path/to/compile/dir/file.gcda
|
|
The actual gcov data file as understood by the gcov
|
|
tool. Resets file coverage data to zero when written to.
|
|
|
|
/sys/kernel/debug/gcov/path/to/compile/dir/file.gcno
|
|
Symbolic link to a static data file required by the gcov
|
|
tool. This file is generated by gcc when compiling with
|
|
option -ftest-coverage.
|
|
|
|
|
|
5. Modules
|
|
==========
|
|
|
|
Kernel modules may contain cleanup code which is only run during
|
|
module unload time. The gcov mechanism provides a means to collect
|
|
coverage data for such code by keeping a copy of the data associated
|
|
with the unloaded module. This data remains available through debugfs.
|
|
Once the module is loaded again, the associated coverage counters are
|
|
initialized with the data from its previous instantiation.
|
|
|
|
This behavior can be deactivated by specifying the gcov_persist kernel
|
|
parameter:
|
|
|
|
gcov_persist=0
|
|
|
|
At run-time, a user can also choose to discard data for an unloaded
|
|
module by writing to its data file or the global reset file.
|
|
|
|
|
|
6. Separated build and test machines
|
|
====================================
|
|
|
|
The gcov kernel profiling infrastructure is designed to work out-of-the
|
|
box for setups where kernels are built and run on the same machine. In
|
|
cases where the kernel runs on a separate machine, special preparations
|
|
must be made, depending on where the gcov tool is used:
|
|
|
|
a) gcov is run on the TEST machine
|
|
|
|
The gcov tool version on the test machine must be compatible with the
|
|
gcc version used for kernel build. Also the following files need to be
|
|
copied from build to test machine:
|
|
|
|
from the source tree:
|
|
- all C source files + headers
|
|
|
|
from the build tree:
|
|
- all C source files + headers
|
|
- all .gcda and .gcno files
|
|
- all links to directories
|
|
|
|
It is important to note that these files need to be placed into the
|
|
exact same file system location on the test machine as on the build
|
|
machine. If any of the path components is symbolic link, the actual
|
|
directory needs to be used instead (due to make's CURDIR handling).
|
|
|
|
b) gcov is run on the BUILD machine
|
|
|
|
The following files need to be copied after each test case from test
|
|
to build machine:
|
|
|
|
from the gcov directory in sysfs:
|
|
- all .gcda files
|
|
- all links to .gcno files
|
|
|
|
These files can be copied to any location on the build machine. gcov
|
|
must then be called with the -o option pointing to that directory.
|
|
|
|
Example directory setup on the build machine:
|
|
|
|
/tmp/linux: kernel source tree
|
|
/tmp/out: kernel build directory as specified by make O=
|
|
/tmp/coverage: location of the files copied from the test machine
|
|
|
|
[user@build] cd /tmp/out
|
|
[user@build] gcov -o /tmp/coverage/tmp/out/init main.c
|
|
|
|
|
|
7. Troubleshooting
|
|
==================
|
|
|
|
Problem: Compilation aborts during linker step.
|
|
Cause: Profiling flags are specified for source files which are not
|
|
linked to the main kernel or which are linked by a custom
|
|
linker procedure.
|
|
Solution: Exclude affected source files from profiling by specifying
|
|
GCOV_PROFILE := n or GCOV_PROFILE_basename.o := n in the
|
|
corresponding Makefile.
|
|
|
|
Problem: Files copied from sysfs appear empty or incomplete.
|
|
Cause: Due to the way seq_file works, some tools such as cp or tar
|
|
may not correctly copy files from sysfs.
|
|
Solution: Use 'cat' to read .gcda files and 'cp -d' to copy links.
|
|
Alternatively use the mechanism shown in Appendix B.
|
|
|
|
|
|
Appendix A: gather_on_build.sh
|
|
==============================
|
|
|
|
Sample script to gather coverage meta files on the build machine
|
|
(see 6a):
|
|
#!/bin/bash
|
|
|
|
KSRC=$1
|
|
KOBJ=$2
|
|
DEST=$3
|
|
|
|
if [ -z "$KSRC" ] || [ -z "$KOBJ" ] || [ -z "$DEST" ]; then
|
|
echo "Usage: $0 <ksrc directory> <kobj directory> <output.tar.gz>" >&2
|
|
exit 1
|
|
fi
|
|
|
|
KSRC=$(cd $KSRC; printf "all:\n\t@echo \${CURDIR}\n" | make -f -)
|
|
KOBJ=$(cd $KOBJ; printf "all:\n\t@echo \${CURDIR}\n" | make -f -)
|
|
|
|
find $KSRC $KOBJ \( -name '*.gcno' -o -name '*.[ch]' -o -type l \) -a \
|
|
-perm /u+r,g+r | tar cfz $DEST -P -T -
|
|
|
|
if [ $? -eq 0 ] ; then
|
|
echo "$DEST successfully created, copy to test system and unpack with:"
|
|
echo " tar xfz $DEST -P"
|
|
else
|
|
echo "Could not create file $DEST"
|
|
fi
|
|
|
|
|
|
Appendix B: gather_on_test.sh
|
|
=============================
|
|
|
|
Sample script to gather coverage data files on the test machine
|
|
(see 6b):
|
|
|
|
#!/bin/bash -e
|
|
|
|
DEST=$1
|
|
GCDA=/sys/kernel/debug/gcov
|
|
|
|
if [ -z "$DEST" ] ; then
|
|
echo "Usage: $0 <output.tar.gz>" >&2
|
|
exit 1
|
|
fi
|
|
|
|
TEMPDIR=$(mktemp -d)
|
|
echo Collecting data..
|
|
find $GCDA -type d -exec mkdir -p $TEMPDIR/\{\} \;
|
|
find $GCDA -name '*.gcda' -exec sh -c 'cat < $0 > '$TEMPDIR'/$0' {} \;
|
|
find $GCDA -name '*.gcno' -exec sh -c 'cp -d $0 '$TEMPDIR'/$0' {} \;
|
|
tar czf $DEST -C $TEMPDIR sys
|
|
rm -rf $TEMPDIR
|
|
|
|
echo "$DEST successfully created, copy to build system and unpack with:"
|
|
echo " tar xfz $DEST"
|