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Diffstat (limited to 'Documentation/dev-tools/kgdb.rst')
| -rw-r--r-- | Documentation/dev-tools/kgdb.rst | 59 |
1 files changed, 41 insertions, 18 deletions
diff --git a/Documentation/dev-tools/kgdb.rst b/Documentation/dev-tools/kgdb.rst index d38be58f872a..f83ba2601e55 100644 --- a/Documentation/dev-tools/kgdb.rst +++ b/Documentation/dev-tools/kgdb.rst @@ -63,10 +63,9 @@ will want to turn on ``CONFIG_DEBUG_INFO`` which is called 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 -to 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. +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 @@ -274,6 +273,30 @@ don't like this are to hack gdb to send the :kbd:`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`` ------------------------------ @@ -292,7 +315,7 @@ driver as a loadable kernel module kgdbwait will not do anything. Kernel parameter: ``kgdbcon`` ----------------------------- -The ``kgdbcon`` feature allows you to see :c:func:`printk` messages inside gdb +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. @@ -379,7 +402,7 @@ This is a quick example of how to use kdb. 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 :kbd:`SysRq-G`, which means you must have - enabled ``CONFIG_MAGIC_SysRq=y`` in your kernel config. + enabled ``CONFIG_MAGIC_SYSRQ=y`` in your kernel config. - When logged in as root or with a super user session you can run:: @@ -408,7 +431,7 @@ This is a quick example of how to use kdb. ``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 :c:func:`dump_stack` + ``bt`` Get a backtrace of the current process using dump_stack() ``dmesg`` View the kernel syslog buffer ``go`` Continue the system =========== ================================================================= @@ -438,7 +461,7 @@ This is a quick example of how to use kdb with a keyboard. 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 :kbd:`SysRq-G`, which means you must have - enabled ``CONFIG_MAGIC_SysRq=y`` in your kernel config. + enabled ``CONFIG_MAGIC_SYSRQ=y`` in your kernel config. - When logged in as root or with a super user session you can run:: @@ -534,7 +557,7 @@ Connecting with gdb to a serial port Example (using a directly connected port):: % gdb ./vmlinux - (gdb) set remotebaud 115200 + (gdb) set serial baud 115200 (gdb) target remote /dev/ttyS0 @@ -700,9 +723,9 @@ The kernel debugger is organized into a number of components: The arch-specific portion implements: - contains an arch-specific trap catcher which invokes - :c:func:`kgdb_handle_exception` to start kgdb about doing its work + kgdb_handle_exception() to start kgdb about doing its work - - translation to and from gdb specific packet format to :c:type:`pt_regs` + - translation to and from gdb specific packet format to struct pt_regs - Registration and unregistration of architecture specific trap hooks @@ -745,7 +768,7 @@ The kernel debugger is organized into a number of components: config. Later run ``modprobe kdb_hello`` and the next time you enter the kdb shell, you can run the ``hello`` command. - - The implementation for :c:func:`kdb_printf` which emits messages directly + - The implementation for kdb_printf() which emits messages directly to I/O drivers, bypassing the kernel log. - SW / HW breakpoint management for the kdb shell @@ -822,7 +845,7 @@ invokes a callback in the serial core which in turn uses the callback in the UART driver. When using kgdboc with a UART, the UART driver must implement two -callbacks in the :c:type:`struct uart_ops <uart_ops>`. +callbacks in the struct uart_ops. Example from ``drivers/8250.c``:: @@ -848,10 +871,10 @@ The kgdboc driver contains logic to configure communications with an attached keyboard. The keyboard infrastructure is only compiled into the kernel when ``CONFIG_KDB_KEYBOARD=y`` is set in the kernel configuration. -The core polled keyboard driver driver for PS/2 type keyboards is in +The core polled keyboard driver for PS/2 type keyboards is in ``drivers/char/kdb_keyboard.c``. This driver is hooked into the debug core when kgdboc populates the callback in the array called -:c:type:`kdb_poll_funcs[]`. The :c:func:`kdb_get_kbd_char` is the top-level +:c:expr:`kdb_poll_funcs[]`. The kdb_get_kbd_char() is the top-level function which polls hardware for single character input. kgdboc and kms @@ -863,10 +886,10 @@ that you have a video driver which has a frame buffer console and atomic kernel mode setting support. Every time the kernel debugger is entered it calls -:c:func:`kgdboc_pre_exp_handler` which in turn calls :c:func:`con_debug_enter` +kgdboc_pre_exp_handler() which in turn calls con_debug_enter() in the virtual console layer. On resuming kernel execution, the kernel -debugger calls :c:func:`kgdboc_post_exp_handler` which in turn calls -:c:func:`con_debug_leave`. +debugger calls kgdboc_post_exp_handler() which in turn calls +con_debug_leave(). Any video driver that wants to be compatible with the kernel debugger and the atomic kms callbacks must implement the ``mode_set_base_atomic``, |