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Commit e349b1b7 authored by Jonathan Corbet's avatar Jonathan Corbet
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Merge branch 'doc/4.9' into docs-next

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Documentation/gdb-kernel-debugging.txt → Documentation/dev-tools/gdb-kernel-debugging.rst
View file @ e349b1b7
.. highlight:: none
Debugging kernel and modules via gdb
====================================
......@@ -13,54 +15,58 @@ be transferred to the other gdb stubs as well.
Requirements
------------
o gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true
for distributions)
- gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true
for distributions)
Setup
-----
o Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and
www.qemu.org for more details). For cross-development,
http://landley.net/aboriginal/bin keeps a pool of machine images and
toolchains that can be helpful to start from.
- Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and
www.qemu.org for more details). For cross-development,
http://landley.net/aboriginal/bin keeps a pool of machine images and
toolchains that can be helpful to start from.
o Build the kernel with CONFIG_GDB_SCRIPTS enabled, but leave
CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports
CONFIG_FRAME_POINTER, keep it enabled.
- Build the kernel with CONFIG_GDB_SCRIPTS enabled, but leave
CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports
CONFIG_FRAME_POINTER, keep it enabled.
o Install that kernel on the guest.
- Install that kernel on the guest.
Alternatively, QEMU allows to boot the kernel directly using -kernel,
-append, -initrd command line switches. This is generally only useful if
you do not depend on modules. See QEMU documentation for more details on
this mode.
Alternatively, QEMU allows to boot the kernel directly using -kernel,
-append, -initrd command line switches. This is generally only useful if
you do not depend on modules. See QEMU documentation for more details on
this mode.
- Enable the gdb stub of QEMU/KVM, either
o Enable the gdb stub of QEMU/KVM, either
- at VM startup time by appending "-s" to the QEMU command line
or
or
- during runtime by issuing "gdbserver" from the QEMU monitor
console
o cd /path/to/linux-build
- cd /path/to/linux-build
o Start gdb: gdb vmlinux
- Start gdb: gdb vmlinux
Note: Some distros may restrict auto-loading of gdb scripts to known safe
directories. In case gdb reports to refuse loading vmlinux-gdb.py, add
Note: Some distros may restrict auto-loading of gdb scripts to known safe
directories. In case gdb reports to refuse loading vmlinux-gdb.py, add::
add-auto-load-safe-path /path/to/linux-build
to ~/.gdbinit. See gdb help for more details.
to ~/.gdbinit. See gdb help for more details.
- Attach to the booted guest::
o Attach to the booted guest:
(gdb) target remote :1234
Examples of using the Linux-provided gdb helpers
------------------------------------------------
o Load module (and main kernel) symbols:
- Load module (and main kernel) symbols::
(gdb) lx-symbols
loading vmlinux
scanning for modules in /home/user/linux/build
......@@ -72,17 +78,20 @@ Examples of using the Linux-provided gdb helpers
...
loading @0xffffffffa0000000: /home/user/linux/build/drivers/ata/ata_generic.ko
o Set a breakpoint on some not yet loaded module function, e.g.:
- Set a breakpoint on some not yet loaded module function, e.g.::
(gdb) b btrfs_init_sysfs
Function "btrfs_init_sysfs" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (btrfs_init_sysfs) pending.
o Continue the target
- Continue the target::
(gdb) c
o Load the module on the target and watch the symbols being loaded as well as
the breakpoint hit:
- Load the module on the target and watch the symbols being loaded as well as
the breakpoint hit::
loading @0xffffffffa0034000: /home/user/linux/build/lib/libcrc32c.ko
loading @0xffffffffa0050000: /home/user/linux/build/lib/lzo/lzo_compress.ko
loading @0xffffffffa006e000: /home/user/linux/build/lib/zlib_deflate/zlib_deflate.ko
......@@ -91,7 +100,8 @@ Examples of using the Linux-provided gdb helpers
Breakpoint 1, btrfs_init_sysfs () at /home/user/linux/fs/btrfs/sysfs.c:36
36 btrfs_kset = kset_create_and_add("btrfs", NULL, fs_kobj);
o Dump the log buffer of the target kernel:
- Dump the log buffer of the target kernel::
(gdb) lx-dmesg
[ 0.000000] Initializing cgroup subsys cpuset
[ 0.000000] Initializing cgroup subsys cpu
......@@ -102,19 +112,22 @@ Examples of using the Linux-provided gdb helpers
[ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
....
o Examine fields of the current task struct:
- Examine fields of the current task struct::
(gdb) p $lx_current().pid
$1 = 4998
(gdb) p $lx_current().comm
$2 = "modprobe\000\000\000\000\000\000\000"
o Make use of the per-cpu function for the current or a specified CPU:
- Make use of the per-cpu function for the current or a specified CPU::
(gdb) p $lx_per_cpu("runqueues").nr_running
$3 = 1
(gdb) p $lx_per_cpu("runqueues", 2).nr_running
$4 = 0
o Dig into hrtimers using the container_of helper:
- Dig into hrtimers using the container_of helper::
(gdb) set $next = $lx_per_cpu("hrtimer_bases").clock_base[0].active.next
(gdb) p *$container_of($next, "struct hrtimer", "node")
$5 = {
......@@ -144,7 +157,7 @@ List of commands and functions
------------------------------
The number of commands and convenience functions may evolve over the time,
this is just a snapshot of the initial version:
this is just a snapshot of the initial version::
(gdb) apropos lx
function lx_current -- Return current task
......
Documentation/kcov.txt → Documentation/dev-tools/kcov.rst
View file @ e349b1b7
......@@ -12,38 +12,38 @@ To achieve this goal it does not collect coverage in soft/hard interrupts
and instrumentation of some inherently non-deterministic parts of kernel is
disbled (e.g. scheduler, locking).
Usage:
======
Usage
-----
Configure kernel with:
Configure the kernel with::
CONFIG_KCOV=y
CONFIG_KCOV requires gcc built on revision 231296 or later.
Profiling data will only become accessible once debugfs has been mounted:
Profiling data will only become accessible once debugfs has been mounted::
mount -t debugfs none /sys/kernel/debug
The following program demonstrates kcov usage from within a test program:
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
#define KCOV_ENABLE _IO('c', 100)
#define KCOV_DISABLE _IO('c', 101)
#define COVER_SIZE (64<<10)
int main(int argc, char **argv)
{
The following program demonstrates kcov usage from within a test program::
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#define KCOV_INIT_TRACE _IOR('c', 1, unsigned long)
#define KCOV_ENABLE _IO('c', 100)
#define KCOV_DISABLE _IO('c', 101)
#define COVER_SIZE (64<<10)
int main(int argc, char **argv)
{
int fd;
unsigned long *cover, n, i;
......@@ -83,24 +83,24 @@ int main(int argc, char **argv)
if (close(fd))
perror("close"), exit(1);
return 0;
}
After piping through addr2line output of the program looks as follows:
SyS_read
fs/read_write.c:562
__fdget_pos
fs/file.c:774
__fget_light
fs/file.c:746
__fget_light
fs/file.c:750
__fget_light
fs/file.c:760
__fdget_pos
fs/file.c:784
SyS_read
fs/read_write.c:562
}
After piping through addr2line output of the program looks as follows::
SyS_read
fs/read_write.c:562
__fdget_pos
fs/file.c:774
__fget_light
fs/file.c:746
__fget_light
fs/file.c:750
__fget_light
fs/file.c:760
__fdget_pos
fs/file.c:784
SyS_read
fs/read_write.c:562
If a program needs to collect coverage from several threads (independently),
it needs to open /sys/kernel/debug/kcov in each thread separately.
......
Documentation/kmemleak.txt → Documentation/dev-tools/kmemleak.rst
View file @ e349b1b7
Kernel Memory Leak Detector
===========================
Introduction
------------
Kmemleak provides a way of detecting possible kernel memory leaks in a
way similar to a tracing garbage collector
(https://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29#Tracing_garbage_collectors),
with the difference that the orphan objects are not freed but only
reported via /sys/kernel/debug/kmemleak. A similar method is used by the
Valgrind tool (memcheck --leak-check) to detect the memory leaks in
Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in
user-space applications.
Kmemleak is supported on x86, arm, powerpc, sparc, sh, microblaze, ppc, mips, s390, metag and tile.
......@@ -19,20 +16,20 @@ Usage
CONFIG_DEBUG_KMEMLEAK in "Kernel hacking" has to be enabled. A kernel
thread scans the memory every 10 minutes (by default) and prints the
number of new unreferenced objects found. To display the details of all
the possible memory leaks:
the possible memory leaks::
# mount -t debugfs nodev /sys/kernel/debug/
# cat /sys/kernel/debug/kmemleak
To trigger an intermediate memory scan:
To trigger an intermediate memory scan::
# echo scan > /sys/kernel/debug/kmemleak
To clear the list of all current possible memory leaks:
To clear the list of all current possible memory leaks::
# echo clear > /sys/kernel/debug/kmemleak
New leaks will then come up upon reading /sys/kernel/debug/kmemleak
New leaks will then come up upon reading ``/sys/kernel/debug/kmemleak``
again.
Note that the orphan objects are listed in the order they were allocated
......@@ -40,22 +37,31 @@ and one object at the beginning of the list may cause other subsequent
objects to be reported as orphan.
Memory scanning parameters can be modified at run-time by writing to the
/sys/kernel/debug/kmemleak file. The following parameters are supported:
off - disable kmemleak (irreversible)
stack=on - enable the task stacks scanning (default)
stack=off - disable the tasks stacks scanning
scan=on - start the automatic memory scanning thread (default)
scan=off - stop the automatic memory scanning thread
scan=<secs> - set the automatic memory scanning period in seconds
(default 600, 0 to stop the automatic scanning)
scan - trigger a memory scan
clear - clear list of current memory leak suspects, done by
marking all current reported unreferenced objects grey,
or free all kmemleak objects if kmemleak has been disabled.
dump=<addr> - dump information about the object found at <addr>
Kmemleak can also be disabled at boot-time by passing "kmemleak=off" on
``/sys/kernel/debug/kmemleak`` file. The following parameters are supported:
- off
disable kmemleak (irreversible)
- stack=on
enable the task stacks scanning (default)
- stack=off
disable the tasks stacks scanning
- scan=on
start the automatic memory scanning thread (default)
- scan=off
stop the automatic memory scanning thread
- scan=<secs>
set the automatic memory scanning period in seconds
(default 600, 0 to stop the automatic scanning)
- scan
trigger a memory scan
- clear
clear list of current memory leak suspects, done by
marking all current reported unreferenced objects grey,
or free all kmemleak objects if kmemleak has been disabled.
- dump=<addr>
dump information about the object found at <addr>
Kmemleak can also be disabled at boot-time by passing ``kmemleak=off`` on
the kernel command line.
Memory may be allocated or freed before kmemleak is initialised and
......@@ -63,13 +69,14 @@ these actions are stored in an early log buffer. The size of this buffer
is configured via the CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE option.
If CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF are enabled, the kmemleak is
disabled by default. Passing "kmemleak=on" on the kernel command
disabled by default. Passing ``kmemleak=on`` on the kernel command
line enables the function.
Basic Algorithm
---------------
The memory allocations via kmalloc, vmalloc, kmem_cache_alloc and
The memory allocations via :c:func:`kmalloc`, :c:func:`vmalloc`,
:c:func:`kmem_cache_alloc` and
friends are traced and the pointers, together with additional
information like size and stack trace, are stored in a rbtree.
The corresponding freeing function calls are tracked and the pointers
......@@ -113,13 +120,13 @@ when doing development. To work around these situations you can use the
you can find new unreferenced objects; this should help with testing
specific sections of code.
To test a critical section on demand with a clean kmemleak do:
To test a critical section on demand with a clean kmemleak do::
# echo clear > /sys/kernel/debug/kmemleak
... test your kernel or modules ...
# echo scan > /sys/kernel/debug/kmemleak
Then as usual to get your report with:
Then as usual to get your report with::
# cat /sys/kernel/debug/kmemleak
......@@ -131,7 +138,7 @@ disabled by the user or due to an fatal error, internal kmemleak objects
won't be freed when kmemleak is disabled, and those objects may occupy
a large part of physical memory.
In this situation, you may reclaim memory with:
In this situation, you may reclaim memory with::
# echo clear > /sys/kernel/debug/kmemleak
......@@ -140,20 +147,20 @@ Kmemleak API
See the include/linux/kmemleak.h header for the functions prototype.
kmemleak_init - initialize kmemleak
kmemleak_alloc - notify of a memory block allocation
kmemleak_alloc_percpu - notify of a percpu memory block allocation
kmemleak_free - notify of a memory block freeing
kmemleak_free_part - notify of a partial memory block freeing
kmemleak_free_percpu - notify of a percpu memory block freeing
kmemleak_update_trace - update object allocation stack trace
kmemleak_not_leak - mark an object as not a leak
kmemleak_ignore - do not scan or report an object as leak
kmemleak_scan_area - add scan areas inside a memory block
kmemleak_no_scan - do not scan a memory block
kmemleak_erase - erase an old value in a pointer variable
kmemleak_alloc_recursive - as kmemleak_alloc but checks the recursiveness
kmemleak_free_recursive - as kmemleak_free but checks the recursiveness
- ``kmemleak_init`` - initialize kmemleak
- ``kmemleak_alloc`` - notify of a memory block allocation
- ``kmemleak_alloc_percpu`` - notify of a percpu memory block allocation
- ``kmemleak_free`` - notify of a memory block freeing
- ``kmemleak_free_part`` - notify of a partial memory block freeing
- ``kmemleak_free_percpu`` - notify of a percpu memory block freeing
- ``kmemleak_update_trace`` - update object allocation stack trace
- ``kmemleak_not_leak`` - mark an object as not a leak
- ``kmemleak_ignore`` - do not scan or report an object as leak
- ``kmemleak_scan_area`` - add scan areas inside a memory block
- ``kmemleak_no_scan`` - do not scan a memory block
- ``kmemleak_erase`` - erase an old value in a pointer variable
- ``kmemleak_alloc_recursive`` - as kmemleak_alloc but checks the recursiveness
- ``kmemleak_free_recursive`` - as kmemleak_free but checks the recursiveness
Dealing with false positives/negatives
--------------------------------------
......
Documentation/sparse.txt → Documentation/dev-tools/sparse.rst
View file @ e349b1b7
Copyright 2004 Linus Torvalds
Copyright 2004 Pavel Machek <pavel@ucw.cz>
Copyright 2006 Bob Copeland <me@bobcopeland.com>
.. Copyright 2004 Linus Torvalds
.. Copyright 2004 Pavel Machek <pavel@ucw.cz>
.. Copyright 2006 Bob Copeland <me@bobcopeland.com>
Sparse
======
Sparse is a semantic checker for C programs; it can be used to find a
number of potential problems with kernel code. See
https://lwn.net/Articles/689907/ for an overview of sparse; this document
contains some kernel-specific sparse information.
Using sparse for typechecking
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-----------------------------
"__bitwise" is a type attribute, so you have to do something like this:
"__bitwise" is a type attribute, so you have to do something like this::
typedef int __bitwise pm_request_t;
......@@ -20,13 +29,13 @@ but in this case we really _do_ want to force the conversion). And because
the enum values are all the same type, now "enum pm_request" will be that
type too.
And with gcc, all the __bitwise/__force stuff goes away, and it all ends
up looking just like integers to gcc.
And with gcc, all the "__bitwise"/"__force stuff" goes away, and it all
ends up looking just like integers to gcc.
Quite frankly, you don't need the enum there. The above all really just
boils down to one special "int __bitwise" type.
So the simpler way is to just do
So the simpler way is to just do::
typedef int __bitwise pm_request_t;
......@@ -50,7 +59,7 @@ __bitwise - noisy stuff; in particular, __le*/__be* are that. We really
don't want to drown in noise unless we'd explicitly asked for it.
Using sparse for lock checking
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
------------------------------
The following macros are undefined for gcc and defined during a sparse
run to use the "context" tracking feature of sparse, applied to
......@@ -69,22 +78,22 @@ annotation is needed. The tree annotations above are for cases where
sparse would otherwise report a context imbalance.
Getting sparse
~~~~~~~~~~~~~~
--------------
You can get latest released versions from the Sparse homepage at
https://sparse.wiki.kernel.org/index.php/Main_Page
Alternatively, you can get snapshots of the latest development version
of sparse using git to clone..
of sparse using git to clone::
git://git.kernel.org/pub/scm/devel/sparse/sparse.git
DaveJ has hourly generated tarballs of the git tree available at..
DaveJ has hourly generated tarballs of the git tree available at::
http://www.codemonkey.org.uk/projects/git-snapshots/sparse/
Once you have it, just do
Once you have it, just do::
make
make install
......@@ -92,7 +101,7 @@ Once you have it, just do
as a regular user, and it will install sparse in your ~/bin directory.
Using sparse
~~~~~~~~~~~~
------------
Do a kernel make with "make C=1" to run sparse on all the C files that get
recompiled, or use "make C=2" to run sparse on the files whether they need to
......@@ -101,7 +110,7 @@ have already built it.
The optional make variable CF can be used to pass arguments to sparse. The
build system passes -Wbitwise to sparse automatically. To perform endianness
checks, you may define __CHECK_ENDIAN__:
checks, you may define __CHECK_ENDIAN__::
make C=2 CF="-D__CHECK_ENDIAN__"
......
Documentation/dev-tools/tools.rst 0 → 100644
View file @ e349b1b7
================================
Development tools for the kernel
================================
This document is a collection of documents about development tools that can
be used to work on the kernel. For now, the documents have been pulled
together without any significant effot to integrate them into a coherent
whole; patches welcome!
.. class:: toc-title
Table of contents
.. toctree::
:maxdepth: 2
coccinelle
sparse
kcov
gcov
kasan
ubsan
kmemleak
kmemcheck
gdb-kernel-debugging
Documentation/ubsan.txt → Documentation/dev-tools/ubsan.rst
View file @ e349b1b7
Undefined Behavior Sanitizer - UBSAN
Overview
--------
The Undefined Behavior Sanitizer - UBSAN
========================================
UBSAN is a runtime undefined behaviour checker.
......@@ -10,11 +8,13 @@ Compiler inserts code that perform certain kinds of checks before operations
that may cause UB. If check fails (i.e. UB detected) __ubsan_handle_*
function called to print error message.
GCC has that feature since 4.9.x [1] (see -fsanitize=undefined option and
its suboptions). GCC 5.x has more checkers implemented [2].
GCC has that feature since 4.9.x [1_] (see ``-fsanitize=undefined`` option and
its suboptions). GCC 5.x has more checkers implemented [2_].
Report example
---------------
--------------
::
================================================================================
UBSAN: Undefined behaviour in ../include/linux/bitops.h:110:33
......@@ -47,29 +47,33 @@ Report example
Usage
-----
To enable UBSAN configure kernel with:
To enable UBSAN configure kernel with::
CONFIG_UBSAN=y
and to check the entire kernel:
and to check the entire kernel::
CONFIG_UBSAN_SANITIZE_ALL=y
To enable instrumentation 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):
UBSAN_SANITIZE_main.o := y
- For a single file (e.g. main.o)::
UBSAN_SANITIZE_main.o := y
For all files in one directory:
UBSAN_SANITIZE := y
- For all files in one directory::
UBSAN_SANITIZE := y
To exclude files from being instrumented even if
CONFIG_UBSAN_SANITIZE_ALL=y, use:
``CONFIG_UBSAN_SANITIZE_ALL=y``, use::
UBSAN_SANITIZE_main.o := n
and::
UBSAN_SANITIZE_main.o := n
and:
UBSAN_SANITIZE := n
UBSAN_SANITIZE := n
Detection of unaligned accesses controlled through the separate option -
CONFIG_UBSAN_ALIGNMENT. It's off by default on architectures that support
......@@ -80,5 +84,5 @@ reports.
References
----------
[1] - https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html
[2] - https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
.. _1: https://gcc.gnu.org/onlinedocs/gcc-4.9.0/gcc/Debugging-Options.html
.. _2: https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
Documentation/index.rst
View file @ e349b1b7
......@@ -12,6 +12,7 @@ Contents:
:maxdepth: 2
kernel-documentation
dev-tools/tools
media/index
gpu/index
......
MAINTAINERS
View file @ e349b1b7
......@@ -3124,7 +3124,7 @@ L: cocci@systeme.lip6.fr (moderated for non-subscribers)
T: git git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild.git misc
W: http://coccinelle.lip6.fr/
S: Supported
F: Documentation/coccinelle.txt
F: Documentation/dev-tools/coccinelle.rst
F: scripts/coccinelle/
F: scripts/coccicheck
......@@ -5118,7 +5118,7 @@ GCOV BASED KERNEL PROFILING
M: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
S: Maintained
F: kernel/gcov/
F: Documentation/gcov.txt
F: Documentation/dev-tools/gcov.rst
GDT SCSI DISK ARRAY CONTROLLER DRIVER
M: Achim Leubner <achim_leubner@adaptec.com>
......@@ -6587,7 +6587,7 @@ L: kasan-dev@googlegroups.com
S: Maintained
F: arch/*/include/asm/kasan.h
F: arch/*/mm/kasan_init*
F: Documentation/kasan.txt
F: Documentation/dev-tools/kasan.rst
F: include/linux/kasan*.h
F: lib/test_kasan.c
F: mm/kasan/
......@@ -6803,7 +6803,7 @@ KMEMCHECK
M: Vegard Nossum <vegardno@ifi.uio.no>
M: Pekka Enberg <penberg@kernel.org>
S: Maintained
F: Documentation/kmemcheck.txt
F: Documentation/dev-tools/kmemcheck.rst
F: arch/x86/include/asm/kmemcheck.h
F: arch/x86/mm/kmemcheck/
F: include/linux/kmemcheck.h
......@@ -6812,7 +6812,7 @@ F: mm/kmemcheck.c
KMEMLEAK
M: Catalin Marinas <catalin.marinas@arm.com>
S: Maintained
F: Documentation/kmemleak.txt
F: Documentation/dev-tools/kmemleak.rst
F: include/linux/kmemleak.h
F: mm/kmemleak.c
F: mm/kmemleak-test.c
......
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