131 строка
4.7 KiB
Plaintext
131 строка
4.7 KiB
Plaintext
====================
|
|
DEBUGGING FR-V LINUX
|
|
====================
|
|
|
|
|
|
The kernel contains a GDB stub that talks GDB remote protocol across a serial
|
|
port. This permits GDB to single step through the kernel, set breakpoints and
|
|
trap exceptions that happen in kernel space and interrupt execution. It also
|
|
permits the NMI interrupt button or serial port events to jump the kernel into
|
|
the debugger.
|
|
|
|
On the CPUs that have on-chip UARTs (FR400, FR403, FR405, FR555), the
|
|
GDB stub hijacks a serial port for its own purposes, and makes it
|
|
generate level 15 interrupts (NMI). The kernel proper cannot see the serial
|
|
port in question under these conditions.
|
|
|
|
On the MB93091-VDK CPU boards, the GDB stub uses UART1, which would otherwise
|
|
be /dev/ttyS1. On the MB93093-PDK, the GDB stub uses UART0. Therefore, on the
|
|
PDK there is no externally accessible serial port and the serial port to
|
|
which the touch screen is attached becomes /dev/ttyS0.
|
|
|
|
Note that the GDB stub runs entirely within CPU debug mode, and so should not
|
|
incur any exceptions or interrupts whilst it is active. In particular, note
|
|
that the clock will lose time since it is implemented in software.
|
|
|
|
|
|
==================
|
|
KERNEL PREPARATION
|
|
==================
|
|
|
|
Firstly, a debuggable kernel must be built. To do this, unpack the kernel tree
|
|
and copy the configuration that you wish to use to .config. Then reconfigure
|
|
the following things on the "Kernel Hacking" tab:
|
|
|
|
(*) "Include debugging information"
|
|
|
|
Set this to "Y". This causes all C and Assembly files to be compiled
|
|
to include debugging information.
|
|
|
|
(*) "In-kernel GDB stub"
|
|
|
|
Set this to "Y". This causes the GDB stub to be compiled into the
|
|
kernel.
|
|
|
|
(*) "Immediate activation"
|
|
|
|
Set this to "Y" if you want the GDB stub to activate as soon as possible
|
|
and wait for GDB to connect. This allows you to start tracing right from
|
|
the beginning of start_kernel() in init/main.c.
|
|
|
|
(*) "Console through GDB stub"
|
|
|
|
Set this to "Y" if you wish to be able to use "console=gdb0" on the
|
|
command line. That tells the kernel to pass system console messages to
|
|
GDB (which then prints them on its standard output). This is useful when
|
|
debugging the serial drivers that'd otherwise be used to pass console
|
|
messages to the outside world.
|
|
|
|
Then build as usual, download to the board and execute. Note that if
|
|
"Immediate activation" was selected, then the kernel will wait for GDB to
|
|
attach. If not, then the kernel will boot immediately and GDB will have to
|
|
interupt it or wait for an exception to occur if before doing anything with
|
|
the kernel.
|
|
|
|
|
|
=========================
|
|
KERNEL DEBUGGING WITH GDB
|
|
=========================
|
|
|
|
Set the serial port on the computer that's going to run GDB to the appropriate
|
|
baud rate. Assuming the board's debug port is connected to ttyS0/COM1 on the
|
|
computer doing the debugging:
|
|
|
|
stty -F /dev/ttyS0 115200
|
|
|
|
Then start GDB in the base of the kernel tree:
|
|
|
|
frv-uclinux-gdb linux [uClinux]
|
|
|
|
Or:
|
|
|
|
frv-uclinux-gdb vmlinux [MMU linux]
|
|
|
|
When the prompt appears:
|
|
|
|
GNU gdb frv-031024
|
|
Copyright 2003 Free Software Foundation, Inc.
|
|
GDB is free software, covered by the GNU General Public License, and you are
|
|
welcome to change it and/or distribute copies of it under certain conditions.
|
|
Type "show copying" to see the conditions.
|
|
There is absolutely no warranty for GDB. Type "show warranty" for details.
|
|
This GDB was configured as "--host=i686-pc-linux-gnu --target=frv-uclinux"...
|
|
(gdb)
|
|
|
|
Attach to the board like this:
|
|
|
|
(gdb) target remote /dev/ttyS0
|
|
Remote debugging using /dev/ttyS0
|
|
start_kernel () at init/main.c:395
|
|
(gdb)
|
|
|
|
This should show the appropriate lines from the source too. The kernel can
|
|
then be debugged almost as if it's any other program.
|
|
|
|
|
|
===============================
|
|
INTERRUPTING THE RUNNING KERNEL
|
|
===============================
|
|
|
|
The kernel can be interrupted whilst it is running, causing a jump back to the
|
|
GDB stub and the debugger:
|
|
|
|
(*) Pressing Ctrl-C in GDB. This will cause GDB to try and interrupt the
|
|
kernel by sending an RS232 BREAK over the serial line to the GDB
|
|
stub. This will (mostly) immediately interrupt the kernel and return it
|
|
to the debugger.
|
|
|
|
(*) Pressing the NMI button on the board will also cause a jump into the
|
|
debugger.
|
|
|
|
(*) Setting a software breakpoint. This sets a break instruction at the
|
|
desired location which the GDB stub then traps the exception for.
|
|
|
|
(*) Setting a hardware breakpoint. The GDB stub is capable of using the IBAR
|
|
and DBAR registers to assist debugging.
|
|
|
|
Furthermore, the GDB stub will intercept a number of exceptions automatically
|
|
if they are caused by kernel execution. It will also intercept BUG() macro
|
|
invokation.
|
|
|