From e551bd4109d2083bec93d306b44e9b7233224a17 Mon Sep 17 00:00:00 2001 From: Cengiz Can Date: Mon, 2 Dec 2024 09:05:02 +0000 Subject: Documentation: remove :kyb: tags :kyb: is an extra markup that we should avoid when we can. It worsens the plain-text reading experience and adds very little value to rendered views. Remove all :kbd: tags from Documentation/* Signed-off-by: Cengiz Can Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20241202090514.1716-1-cengiz@kernel.wtf --- Documentation/process/email-clients.rst | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'Documentation/process') diff --git a/Documentation/process/email-clients.rst b/Documentation/process/email-clients.rst index e6b9173a1845..84a2450bb6ec 100644 --- a/Documentation/process/email-clients.rst +++ b/Documentation/process/email-clients.rst @@ -86,7 +86,7 @@ In the :menuselection:`Sending Preferences` section: - :menuselection:`Strip Whitespace Before Sending` must be ``disabled`` When composing the message, the cursor should be placed where the patch -should appear, and then pressing :kbd:`CTRL-R` let you specify the patch file +should appear, and then pressing `CTRL-R` let you specify the patch file to insert into the message. Claws Mail (GUI) @@ -94,7 +94,7 @@ Claws Mail (GUI) Works. Some people use this successfully for patches. -To insert a patch use :menuselection:`Message-->Insert File` (:kbd:`CTRL-I`) +To insert a patch use :menuselection:`Message-->Insert File` (`CTRL-I`) or an external editor. If the inserted patch has to be edited in the Claws composition window @@ -108,11 +108,11 @@ Evolution (GUI) Some people use this successfully for patches. When composing mail select: Preformat - from :menuselection:`Format-->Paragraph Style-->Preformatted` (:kbd:`CTRL-7`) + from :menuselection:`Format-->Paragraph Style-->Preformatted` (`CTRL-7`) or the toolbar Then use: -:menuselection:`Insert-->Text File...` (:kbd:`ALT-N x`) +:menuselection:`Insert-->Text File...` (`ALT-N x`) to insert the patch. You can also ``diff -Nru old.c new.c | xclip``, select -- cgit v1.2.3 From 126437fc26be0629585f956b890e6314f56cd63b Mon Sep 17 00:00:00 2001 From: Randy Dunlap Date: Sat, 30 Nov 2024 00:11:06 -0800 Subject: docs: debugging: add more info about devcoredump Correct a few small things in the devcoredump synopsis and then add the devcoredump APIs to it. Fixes: a037699da0a1 ("docs: Add debugging section to process") Signed-off-by: Randy Dunlap Cc: Sebastian Fricke Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Cc: Johannes Berg Cc: Greg Kroah-Hartman Cc: workflows@vger.kernel.org Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20241130081107.552503-1-rdunlap@infradead.org --- .../debugging/driver_development_debugging_guide.rst | 20 ++++++++++++++++---- 1 file changed, 16 insertions(+), 4 deletions(-) (limited to 'Documentation/process') diff --git a/Documentation/process/debugging/driver_development_debugging_guide.rst b/Documentation/process/debugging/driver_development_debugging_guide.rst index aef204094205..46becda8764b 100644 --- a/Documentation/process/debugging/driver_development_debugging_guide.rst +++ b/Documentation/process/debugging/driver_development_debugging_guide.rst @@ -207,17 +207,29 @@ resources, that can cause performance disruptions or even OOM kills. device coredump --------------- -Prerequisite: ``#include `` +Prerequisite: ``CONFIG_DEV_COREDUMP`` & ``#include `` Provides the infrastructure for a driver to provide arbitrary data to userland. It is most often used in conjunction with udev or similar userland application to listen for kernel uevents, which indicate that the dump is ready. Udev has rules to copy that file somewhere for long-term storage and analysis, as by -default, the data for the dump is automatically cleaned up after 5 minutes. -That data is analyzed with driver-specific tools or GDB. +default, the data for the dump is automatically cleaned up after a default +5 minutes. That data is analyzed with driver-specific tools or GDB. + +A device coredump can be created with a vmalloc area, with read/free +methods, or as a scatter/gather list. You can find an example implementation at: `drivers/media/platform/qcom/venus/core.c -`__ +`__, +in the Bluetooth HCI layer, in several wireless drivers, and in several +DRM drivers. + +devcoredump interfaces +~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: include/linux/devcoredump.h + +.. kernel-doc:: drivers/base/devcoredump.c **Copyright** ©2024 : Collabora -- cgit v1.2.3 From 9734b3e753ad4081d8c146e2cae177528246f7ba Mon Sep 17 00:00:00 2001 From: Thorsten Leemhuis Date: Mon, 2 Dec 2024 09:12:19 +0100 Subject: docs: 5.Posting: mentioned Suggested-by: tag Mention the Suggested-by: tag in 5.Posting.rst in a way similar to submitting-patches.rst, which according to the header of the latter is the less detailed document of the two. Reviewed-by: Greg Kroah-Hartman Signed-off-by: Thorsten Leemhuis Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/fbebad6605b02e372b24c2cfa1e05f789fed43d1.1733127086.git.linux@leemhuis.info --- Documentation/process/5.Posting.rst | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'Documentation/process') diff --git a/Documentation/process/5.Posting.rst b/Documentation/process/5.Posting.rst index b3eff03ea249..dbb763a8de90 100644 --- a/Documentation/process/5.Posting.rst +++ b/Documentation/process/5.Posting.rst @@ -261,6 +261,10 @@ The tags in common use are: can be used instead of Closes: if the patch fixes a part of the issue(s) being reported. + - A Suggested-by: tag indicates that the patch idea is suggested by the person + named and ensures credit to the person for the idea. This will, hopefully, + inspire them to help us again in the future. + - Cc: the named person received a copy of the patch and had the opportunity to comment on it. -- cgit v1.2.3 From d5af79c05e9382d38b8546dc5362381ce07ba3d1 Mon Sep 17 00:00:00 2001 From: Randy Dunlap Date: Mon, 9 Dec 2024 16:00:41 -0800 Subject: Documentation: move dev-tools debugging files to process/debugging/ Move gdb and kgdb debugging documentation to the dedicated debugging directory (Documentation/process/debugging/). Adjust the index.rst files to follow the file movement. Adjust files that refer to these moved files to follow the file movement. Update location of kgdb.rst in MAINTAINERS file. Add a link from dev-tools/index to process/debugging/index. Note: translations are not updated. Signed-off-by: Randy Dunlap Cc: Sebastian Fricke Cc: Jonathan Corbet Cc: workflows@vger.kernel.org Cc: Jason Wessel Cc: Daniel Thompson Cc: Douglas Anderson Cc: linux-debuggers@vger.kernel.org Cc: kgdb-bugreport@lists.sourceforge.net Cc: Doug Anderson Cc: Alex Shi Cc: Hu Haowen <2023002089@link.tyut.edu.cn> Cc: Andrew Morton Cc: Greg Kroah-Hartman Cc: linux-serial@vger.kernel.org Acked-by: Greg Kroah-Hartman Acked-by: Daniel Thompson Reviewed-by: Douglas Anderson Signed-off-by: Jonathan Corbet Link: https://lore.kernel.org/r/20241210000041.305477-1-rdunlap@infradead.org --- Documentation/admin-guide/README.rst | 4 +- Documentation/dev-tools/gdb-kernel-debugging.rst | 179 ---- Documentation/dev-tools/index.rst | 5 +- Documentation/dev-tools/kgdb.rst | 937 --------------------- .../process/debugging/gdb-kernel-debugging.rst | 179 ++++ Documentation/process/debugging/index.rst | 2 + Documentation/process/debugging/kgdb.rst | 937 +++++++++++++++++++++ MAINTAINERS | 2 +- include/linux/tty_driver.h | 2 +- lib/Kconfig.debug | 2 +- lib/Kconfig.kgdb | 2 +- 11 files changed, 1127 insertions(+), 1124 deletions(-) delete mode 100644 Documentation/dev-tools/gdb-kernel-debugging.rst delete mode 100644 Documentation/dev-tools/kgdb.rst create mode 100644 Documentation/process/debugging/gdb-kernel-debugging.rst create mode 100644 Documentation/process/debugging/kgdb.rst (limited to 'Documentation/process') diff --git a/Documentation/admin-guide/README.rst b/Documentation/admin-guide/README.rst index f2bebff6a733..eb9452668909 100644 --- a/Documentation/admin-guide/README.rst +++ b/Documentation/admin-guide/README.rst @@ -356,5 +356,5 @@ instructions at 'Documentation/admin-guide/reporting-issues.rst'. Hints on understanding kernel bug reports are in 'Documentation/admin-guide/bug-hunting.rst'. More on debugging the kernel -with gdb is in 'Documentation/dev-tools/gdb-kernel-debugging.rst' and -'Documentation/dev-tools/kgdb.rst'. +with gdb is in 'Documentation/process/debugging/gdb-kernel-debugging.rst' and +'Documentation/process/debugging/kgdb.rst'. diff --git a/Documentation/dev-tools/gdb-kernel-debugging.rst b/Documentation/dev-tools/gdb-kernel-debugging.rst deleted file mode 100644 index 895285c037c7..000000000000 --- a/Documentation/dev-tools/gdb-kernel-debugging.rst +++ /dev/null @@ -1,179 +0,0 @@ -.. highlight:: none - -Debugging kernel and modules via gdb -==================================== - -The kernel debugger kgdb, hypervisors like QEMU or JTAG-based hardware -interfaces allow to debug the Linux kernel and its modules during runtime -using gdb. Gdb comes with a powerful scripting interface for python. The -kernel provides a collection of helper scripts that can simplify typical -kernel debugging steps. This is a short tutorial about how to enable and use -them. It focuses on QEMU/KVM virtual machines as target, but the examples can -be transferred to the other gdb stubs as well. - - -Requirements ------------- - -- gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true - for distributions) - - -Setup ------ - -- Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and - www.qemu.org for more details). For cross-development, - https://landley.net/aboriginal/bin keeps a pool of machine images and - toolchains that can be helpful to start from. - -- 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. - -- Install that kernel on the guest, turn off KASLR if necessary by adding - "nokaslr" to the kernel command line. - 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. In this case, you should build the kernel with - CONFIG_RANDOMIZE_BASE disabled if the architecture supports KASLR. - -- Build the gdb scripts (required on kernels v5.1 and above):: - - make scripts_gdb - -- Enable the gdb stub of QEMU/KVM, either - - - at VM startup time by appending "-s" to the QEMU command line - - or - - - during runtime by issuing "gdbserver" from the QEMU monitor - console - -- cd /path/to/linux-build - -- 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:: - - add-auto-load-safe-path /path/to/linux-build - - to ~/.gdbinit. See gdb help for more details. - -- Attach to the booted guest:: - - (gdb) target remote :1234 - - -Examples of using the Linux-provided gdb helpers ------------------------------------------------- - -- Load module (and main kernel) symbols:: - - (gdb) lx-symbols - loading vmlinux - scanning for modules in /home/user/linux/build - loading @0xffffffffa0020000: /home/user/linux/build/net/netfilter/xt_tcpudp.ko - loading @0xffffffffa0016000: /home/user/linux/build/net/netfilter/xt_pkttype.ko - loading @0xffffffffa0002000: /home/user/linux/build/net/netfilter/xt_limit.ko - loading @0xffffffffa00ca000: /home/user/linux/build/net/packet/af_packet.ko - loading @0xffffffffa003c000: /home/user/linux/build/fs/fuse/fuse.ko - ... - loading @0xffffffffa0000000: /home/user/linux/build/drivers/ata/ata_generic.ko - -- 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. - -- Continue the target:: - - (gdb) c - -- 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 - loading @0xffffffffa01b1000: /home/user/linux/build/fs/btrfs/btrfs.ko - - 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); - -- Dump the log buffer of the target kernel:: - - (gdb) lx-dmesg - [ 0.000000] Initializing cgroup subsys cpuset - [ 0.000000] Initializing cgroup subsys cpu - [ 0.000000] Linux version 3.8.0-rc4-dbg+ (... - [ 0.000000] Command line: root=/dev/sda2 resume=/dev/sda1 vga=0x314 - [ 0.000000] e820: BIOS-provided physical RAM map: - [ 0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable - [ 0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved - .... - -- Examine fields of the current task struct(supported by x86 and arm64 only):: - - (gdb) p $lx_current().pid - $1 = 4998 - (gdb) p $lx_current().comm - $2 = "modprobe\000\000\000\000\000\000\000" - -- 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 - -- 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 = { - node = { - node = { - __rb_parent_color = 18446612133355256072, - rb_right = 0x0 , - rb_left = 0x0 - }, - expires = { - tv64 = 1835268000000 - } - }, - _softexpires = { - tv64 = 1835268000000 - }, - function = 0xffffffff81078232 , - base = 0xffff88003fd0d6f0, - state = 1, - start_pid = 0, - start_site = 0xffffffff81055c1f , - start_comm = "swapper/2\000\000\000\000\000\000" - } - - -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:: - - (gdb) apropos lx - function lx_current -- Return current task - function lx_module -- Find module by name and return the module variable - function lx_per_cpu -- Return per-cpu variable - function lx_task_by_pid -- Find Linux task by PID and return the task_struct variable - function lx_thread_info -- Calculate Linux thread_info from task variable - lx-dmesg -- Print Linux kernel log buffer - lx-lsmod -- List currently loaded modules - lx-symbols -- (Re-)load symbols of Linux kernel and currently loaded modules - -Detailed help can be obtained via "help " for commands and "help -function " for convenience functions. diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst index 3c0ac08b2709..65c54b27a60b 100644 --- a/Documentation/dev-tools/index.rst +++ b/Documentation/dev-tools/index.rst @@ -10,6 +10,9 @@ whole; patches welcome! A brief overview of testing-specific tools can be found in Documentation/dev-tools/testing-overview.rst +Tools that are specific to debugging can be found in +Documentation/process/debugging/index.rst + .. toctree:: :caption: Table of contents :maxdepth: 2 @@ -27,8 +30,6 @@ Documentation/dev-tools/testing-overview.rst kmemleak kcsan kfence - gdb-kernel-debugging - kgdb kselftest kunit/index ktap diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst deleted file mode 100644 index b29b0aac2717..000000000000 --- a/Documentation/dev-tools/kgdb.rst +++ /dev/null @@ -1,937 +0,0 @@ -================================================= -Using kgdb, kdb and the kernel debugger internals -================================================= - -:Author: Jason Wessel - -Introduction -============ - -The kernel has two different debugger front ends (kdb and kgdb) which -interface to the debug core. It is possible to use either of the -debugger front ends and dynamically transition between them if you -configure the kernel properly at compile and runtime. - -Kdb is simplistic shell-style interface which you can use on a system -console with a keyboard or serial console. You can use it to inspect -memory, registers, process lists, dmesg, and even set breakpoints to -stop in a certain location. Kdb is not a source level debugger, although -you can set breakpoints and execute some basic kernel run control. Kdb -is mainly aimed at doing some analysis to aid in development or -diagnosing kernel problems. You can access some symbols by name in -kernel built-ins or in kernel modules if the code was built with -``CONFIG_KALLSYMS``. - -Kgdb is intended to be used as a source level debugger for the Linux -kernel. It is used along with gdb to debug a Linux kernel. The -expectation is that gdb can be used to "break in" to the kernel to -inspect memory, variables and look through call stack information -similar to the way an application developer would use gdb to debug an -application. It is possible to place breakpoints in kernel code and -perform some limited execution stepping. - -Two machines are required for using kgdb. One of these machines is a -development machine and the other is the target machine. The kernel to -be debugged runs on the target machine. The development machine runs an -instance of gdb against the vmlinux file which contains the symbols (not -a boot image such as bzImage, zImage, uImage...). In gdb the developer -specifies the connection parameters and connects to kgdb. The type of -connection a developer makes with gdb depends on the availability of -kgdb I/O modules compiled as built-ins or loadable kernel modules in the -test machine's kernel. - -Compiling a kernel -================== - -- In order to enable compilation of kdb, you must first enable kgdb. - -- The kgdb test compile options are described in the kgdb test suite - chapter. - -Kernel config options for kgdb ------------------------------- - -To enable ``CONFIG_KGDB`` you should look under -:menuselection:`Kernel hacking --> Kernel debugging` and select -:menuselection:`KGDB: kernel debugger`. - -While it is not a hard requirement that you have symbols in your vmlinux -file, gdb tends not to be very useful without the symbolic data, so you -will want to turn on ``CONFIG_DEBUG_INFO`` which is called -:menuselection:`Compile the kernel with debug info` in the config menu. - -It is advised, but not required, that you turn on the -``CONFIG_FRAME_POINTER`` kernel option which is called :menuselection:`Compile -the kernel with frame pointers` in the config menu. This option inserts code -into the compiled executable which saves the frame information in registers -or on the stack at different points which allows a debugger such as gdb to -more accurately construct stack back traces while debugging the kernel. - -If the architecture that you are using supports the kernel option -``CONFIG_STRICT_KERNEL_RWX``, you should consider turning it off. This -option will prevent the use of software breakpoints because it marks -certain regions of the kernel's memory space as read-only. If kgdb -supports it for the architecture you are using, you can use hardware -breakpoints if you desire to run with the ``CONFIG_STRICT_KERNEL_RWX`` -option turned on, else you need to turn off this option. - -Next you should choose one or more I/O drivers to interconnect the debugging -host and debugged target. Early boot debugging requires a KGDB I/O -driver that supports early debugging and the driver must be built into -the kernel directly. Kgdb I/O driver configuration takes place via -kernel or module parameters which you can learn more about in the -section that describes the parameter kgdboc. - -Here is an example set of ``.config`` symbols to enable or disable for kgdb:: - - # CONFIG_STRICT_KERNEL_RWX is not set - CONFIG_FRAME_POINTER=y - CONFIG_KGDB=y - CONFIG_KGDB_SERIAL_CONSOLE=y - -Kernel config options for kdb ------------------------------ - -Kdb is quite a bit more complex than the simple gdbstub sitting on top -of the kernel's debug core. Kdb must implement a shell, and also adds -some helper functions in other parts of the kernel, responsible for -printing out interesting data such as what you would see if you ran -``lsmod``, or ``ps``. In order to build kdb into the kernel you follow the -same steps as you would for kgdb. - -The main config option for kdb is ``CONFIG_KGDB_KDB`` which is called -:menuselection:`KGDB_KDB: include kdb frontend for kgdb` in the config menu. -In theory you would have already also selected an I/O driver such as the -``CONFIG_KGDB_SERIAL_CONSOLE`` interface if you plan on using kdb on a -serial port, when you were configuring kgdb. - -If you want to use a PS/2-style keyboard with kdb, you would select -``CONFIG_KDB_KEYBOARD`` which is called :menuselection:`KGDB_KDB: keyboard as -input device` in the config menu. The ``CONFIG_KDB_KEYBOARD`` option is not -used for anything in the gdb interface to kgdb. The ``CONFIG_KDB_KEYBOARD`` -option only works with kdb. - -Here is an example set of ``.config`` symbols to enable/disable kdb:: - - # CONFIG_STRICT_KERNEL_RWX is not set - CONFIG_FRAME_POINTER=y - CONFIG_KGDB=y - CONFIG_KGDB_SERIAL_CONSOLE=y - CONFIG_KGDB_KDB=y - CONFIG_KDB_KEYBOARD=y - -Kernel Debugger Boot Arguments -============================== - -This section describes the various runtime kernel parameters that affect -the configuration of the kernel debugger. The following chapter covers -using kdb and kgdb as well as providing some examples of the -configuration parameters. - -Kernel parameter: kgdboc ------------------------- - -The kgdboc driver was originally an abbreviation meant to stand for -"kgdb over console". Today it is the primary mechanism to configure how -to communicate from gdb to kgdb as well as the devices you want to use -to interact with the kdb shell. - -For kgdb/gdb, kgdboc is designed to work with a single serial port. It -is intended to cover the circumstance where you want to use a serial -console as your primary console as well as using it to perform kernel -debugging. It is also possible to use kgdb on a serial port which is not -designated as a system console. Kgdboc may be configured as a kernel -built-in or a kernel loadable module. You can only make use of -``kgdbwait`` and early debugging if you build kgdboc into the kernel as -a built-in. - -Optionally you can elect to activate kms (Kernel Mode Setting) -integration. When you use kms with kgdboc and you have a video driver -that has atomic mode setting hooks, it is possible to enter the debugger -on the graphics console. When the kernel execution is resumed, the -previous graphics mode will be restored. This integration can serve as a -useful tool to aid in diagnosing crashes or doing analysis of memory -with kdb while allowing the full graphics console applications to run. - -kgdboc arguments -~~~~~~~~~~~~~~~~ - -Usage:: - - kgdboc=[kms][[,]kbd][[,]serial_device][,baud] - -The order listed above must be observed if you use any of the optional -configurations together. - -Abbreviations: - -- kms = Kernel Mode Setting - -- kbd = Keyboard - -You can configure kgdboc to use the keyboard, and/or a serial device -depending on if you are using kdb and/or kgdb, in one of the following -scenarios. The order listed above must be observed if you use any of the -optional configurations together. Using kms + only gdb is generally not -a useful combination. - -Using loadable module or built-in -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -1. As a kernel built-in: - - Use the kernel boot argument:: - - kgdboc=,[baud] - -2. As a kernel loadable module: - - Use the command:: - - modprobe kgdboc kgdboc=,[baud] - - Here are two examples of how you might format the kgdboc string. The - first is for an x86 target using the first serial port. The second - example is for the ARM Versatile AB using the second serial port. - - 1. ``kgdboc=ttyS0,115200`` - - 2. ``kgdboc=ttyAMA1,115200`` - -Configure kgdboc at runtime with sysfs -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -At run time you can enable or disable kgdboc by writing parameters -into sysfs. Here are two examples: - -1. Enable kgdboc on ttyS0:: - - echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc - -2. Disable kgdboc:: - - echo "" > /sys/module/kgdboc/parameters/kgdboc - -.. note:: - - You do not need to specify the baud if you are configuring the - console on tty which is already configured or open. - -More examples -^^^^^^^^^^^^^ - -You can configure kgdboc to use the keyboard, and/or a serial device -depending on if you are using kdb and/or kgdb, in one of the following -scenarios. - -1. kdb and kgdb over only a serial port:: - - kgdboc=[,baud] - - Example:: - - kgdboc=ttyS0,115200 - -2. kdb and kgdb with keyboard and a serial port:: - - kgdboc=kbd,[,baud] - - Example:: - - kgdboc=kbd,ttyS0,115200 - -3. kdb with a keyboard:: - - kgdboc=kbd - -4. kdb with kernel mode setting:: - - kgdboc=kms,kbd - -5. kdb with kernel mode setting and kgdb over a serial port:: - - kgdboc=kms,kbd,ttyS0,115200 - -.. note:: - - Kgdboc does not support interrupting the target via the gdb remote - protocol. You must manually send a `SysRq-G` unless you have a proxy - that splits console output to a terminal program. A console proxy has a - separate TCP port for the debugger and a separate TCP port for the - "human" console. The proxy can take care of sending the `SysRq-G` - for you. - -When using kgdboc with no debugger proxy, you can end up connecting the -debugger at one of two entry points. If an exception occurs after you -have loaded kgdboc, a message should print on the console stating it is -waiting for the debugger. In this case you disconnect your terminal -program and then connect the debugger in its place. If you want to -interrupt the target system and forcibly enter a debug session you have -to issue a `Sysrq` sequence and then type the letter `g`. Then you -disconnect the terminal session and connect gdb. Your options if you -don't like this are to hack gdb to send the `SysRq-G` for you as well as -on the initial connect, or to use a debugger proxy that allows an -unmodified gdb to do the debugging. - -Kernel parameter: ``kgdboc_earlycon`` -------------------------------------- - -If you specify the kernel parameter ``kgdboc_earlycon`` and your serial -driver registers a boot console that supports polling (doesn't need -interrupts and implements a nonblocking read() function) kgdb will attempt -to work using the boot console until it can transition to the regular -tty driver specified by the ``kgdboc`` parameter. - -Normally there is only one boot console (especially that implements the -read() function) so just adding ``kgdboc_earlycon`` on its own is -sufficient to make this work. If you have more than one boot console you -can add the boot console's name to differentiate. Note that names that -are registered through the boot console layer and the tty layer are not -the same for the same port. - -For instance, on one board to be explicit you might do:: - - kgdboc_earlycon=qcom_geni kgdboc=ttyMSM0 - -If the only boot console on the device was "qcom_geni", you could simplify:: - - kgdboc_earlycon kgdboc=ttyMSM0 - -Kernel parameter: ``kgdbwait`` ------------------------------- - -The Kernel command line option ``kgdbwait`` makes kgdb wait for a -debugger connection during booting of a kernel. You can only use this -option if you compiled a kgdb I/O driver into the kernel and you -specified the I/O driver configuration as a kernel command line option. -The kgdbwait parameter should always follow the configuration parameter -for the kgdb I/O driver in the kernel command line else the I/O driver -will not be configured prior to asking the kernel to use it to wait. - -The kernel will stop and wait as early as the I/O driver and -architecture allows when you use this option. If you build the kgdb I/O -driver as a loadable kernel module kgdbwait will not do anything. - -Kernel parameter: ``kgdbcon`` ------------------------------ - -The ``kgdbcon`` feature allows you to see printk() messages inside gdb -while gdb is connected to the kernel. Kdb does not make use of the kgdbcon -feature. - -Kgdb supports using the gdb serial protocol to send console messages to -the debugger when the debugger is connected and running. There are two -ways to activate this feature. - -1. Activate with the kernel command line option:: - - kgdbcon - -2. Use sysfs before configuring an I/O driver:: - - echo 1 > /sys/module/debug_core/parameters/kgdb_use_con - -.. note:: - - If you do this after you configure the kgdb I/O driver, the - setting will not take effect until the next point the I/O is - reconfigured. - -.. important:: - - You cannot use kgdboc + kgdbcon on a tty that is an - active system console. An example of incorrect usage is:: - - console=ttyS0,115200 kgdboc=ttyS0 kgdbcon - -It is possible to use this option with kgdboc on a tty that is not a -system console. - -Run time parameter: ``kgdbreboot`` ----------------------------------- - -The kgdbreboot feature allows you to change how the debugger deals with -the reboot notification. You have 3 choices for the behavior. The -default behavior is always set to 0. - -.. tabularcolumns:: |p{0.4cm}|p{11.5cm}|p{5.6cm}| - -.. flat-table:: - :widths: 1 10 8 - - * - 1 - - ``echo -1 > /sys/module/debug_core/parameters/kgdbreboot`` - - Ignore the reboot notification entirely. - - * - 2 - - ``echo 0 > /sys/module/debug_core/parameters/kgdbreboot`` - - Send the detach message to any attached debugger client. - - * - 3 - - ``echo 1 > /sys/module/debug_core/parameters/kgdbreboot`` - - Enter the debugger on reboot notify. - -Kernel parameter: ``nokaslr`` ------------------------------ - -If the architecture that you are using enables KASLR by default, -you should consider turning it off. KASLR randomizes the -virtual address where the kernel image is mapped and confuses -gdb which resolves addresses of kernel symbols from the symbol table -of vmlinux. - -Using kdb -========= - -Quick start for kdb on a serial port ------------------------------------- - -This is a quick example of how to use kdb. - -1. Configure kgdboc at boot using kernel parameters:: - - console=ttyS0,115200 kgdboc=ttyS0,115200 nokaslr - - OR - - Configure kgdboc after the kernel has booted; assuming you are using - a serial port console:: - - echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc - -2. Enter the kernel debugger manually or by waiting for an oops or - fault. There are several ways you can enter the kernel debugger - manually; all involve using the `SysRq-G`, which means you must have - enabled ``CONFIG_MAGIC_SYSRQ=y`` in your kernel config. - - - When logged in as root or with a super user session you can run:: - - echo g > /proc/sysrq-trigger - - - Example using minicom 2.2 - - Press: `CTRL-A` `f` `g` - - - When you have telneted to a terminal server that supports sending - a remote break - - Press: `CTRL-]` - - Type in: ``send break`` - - Press: `Enter` `g` - -3. From the kdb prompt you can run the ``help`` command to see a complete - list of the commands that are available. - - Some useful commands in kdb include: - - =========== ================================================================= - ``lsmod`` Shows where kernel modules are loaded - ``ps`` Displays only the active processes - ``ps A`` Shows all the processes - ``summary`` Shows kernel version info and memory usage - ``bt`` Get a backtrace of the current process using dump_stack() - ``dmesg`` View the kernel syslog buffer - ``go`` Continue the system - =========== ================================================================= - -4. When you are done using kdb you need to consider rebooting the system - or using the ``go`` command to resuming normal kernel execution. If you - have paused the kernel for a lengthy period of time, applications - that rely on timely networking or anything to do with real wall clock - time could be adversely affected, so you should take this into - consideration when using the kernel debugger. - -Quick start for kdb using a keyboard connected console ------------------------------------------------------- - -This is a quick example of how to use kdb with a keyboard. - -1. Configure kgdboc at boot using kernel parameters:: - - kgdboc=kbd - - OR - - Configure kgdboc after the kernel has booted:: - - echo kbd > /sys/module/kgdboc/parameters/kgdboc - -2. Enter the kernel debugger manually or by waiting for an oops or - fault. There are several ways you can enter the kernel debugger - manually; all involve using the `SysRq-G`, which means you must have - enabled ``CONFIG_MAGIC_SYSRQ=y`` in your kernel config. - - - When logged in as root or with a super user session you can run:: - - echo g > /proc/sysrq-trigger - - - Example using a laptop keyboard: - - Press and hold down: `Alt` - - Press and hold down: `Fn` - - Press and release the key with the label: `SysRq` - - Release: `Fn` - - Press and release: `g` - - Release: `Alt` - - - Example using a PS/2 101-key keyboard - - Press and hold down: `Alt` - - Press and release the key with the label: `SysRq` - - Press and release: `g` - - Release: `Alt` - -3. Now type in a kdb command such as ``help``, ``dmesg``, ``bt`` or ``go`` to - continue kernel execution. - -Using kgdb / gdb -================ - -In order to use kgdb you must activate it by passing configuration -information to one of the kgdb I/O drivers. If you do not pass any -configuration information kgdb will not do anything at all. Kgdb will -only actively hook up to the kernel trap hooks if a kgdb I/O driver is -loaded and configured. If you unconfigure a kgdb I/O driver, kgdb will -unregister all the kernel hook points. - -All kgdb I/O drivers can be reconfigured at run time, if -``CONFIG_SYSFS`` and ``CONFIG_MODULES`` are enabled, by echo'ing a new -config string to ``/sys/module//parameter/