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Debugging User Mode Applications
Please note that you should always set the correct paths
when debugging an application which uses shared
libraries.
Make Debug
To be able to debug a program, you must build it with
debugging in mind. With the Developer Board 82/LX SDK there is a make target that does this for you, called 'debug'
(check Rules.axis for details). To build your application
for debugging, simply 'make debug' (and 'make nodebug' to
reverse the effect') before 'make' and 'make install'.
Below follows a summary of what 'make debug' does (and what
you need to do if you don't use it).
- Adds -g to the compiler flags. This will
include debug information in the program. (The default debug
format is Dwarf-2.)
- Removes -s (which strips the program from its symbol
information) from the link flags. (If your
program is in ELF format, the 'file' command
will tell you whether it's stripped or not.) The symbols
are only needed on the host side when debugging, and 'make
install' automatically strips the binary when putting it
in the install directory (/bin, for example).
- Turns off optimizations (adds -O0 to the compiler flags).
This makes it easier to debug the program, but it may
affect the behaviour. You can debug optimized code, but be
aware that the compiler has probably rearranged the
execution order of your statements. Also, variables may
have been optimized away.
- Adds -fno-omit-frame-pointer to your
compiler flags. This is a nop when the optimization level
is set to 0, but it's there as a reminder that you should
keep it if you change the debug optimization level (gcc optimizations
starting at -O2 imply -fomit-frame-pointer). The
frame pointer acts as a local stack pointer inside a
function, and will be placed in register r8.
Starting a Program
Telnet, or log in via the serial port (if you have agetty
on that port) to your board. The preferred way to communicate
with gdb on the host side is over TCP/IP.
On the target:
gdbserver [<hostname/ip
address>]:<port> <program>
Example: gdbserver hostname:1234 /tmp/hello_world
Now start gdb-cris on the host. To connect to the target:
target <hostname/ip address>:<port> (make
sure you specify the same port number)
Example: (gdb) target remote 10.13.8.122:2345
To
debug over a serial connection, make sure it is enabled in the
kernel configuration (under "Drivers for Etrax built-in
interfaces") and not used for anything else. One of the
ports is often used by the kernel for debug printouts, or
agetty might be using it (check your /etc/inittab). On the
target:
gdbserver <device> <program>
Example: gdbserver /dev/ttyS2 /tmp/hello_world
Then start gdb-cris on the host. To connect you need
to specify what device on the host you have connected the
serial cable to:
target remote <device>
Example: (gdb) target remote /dev/ttyS0
After you have connected to the target, you will end up in
the startup routine for the C library the application is using
(often called _start). To get to the main function of your
application, simply
(gdb) until main
Attaching to a Process
You may attach to an already running process by giving
the process id as an argument to the gdbserver:
gdbserver [<hostname/ip
address/device>]:<port> <pid>
Example: gdbserver hostname:2345 32
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