Debug build of the application

First, prepare the application source code (hello_world.c).

Next, build the application, but run "nios2-linux-uclibc-gcc" with the "-g" option to add debug information.

In addition, in the case of μClinux, it is necessary to use a flat binary format executable file, so add “-elf2flt” to the option.

If it finishes without errors, an executable file (hello) and a debug information file (hello.gdb) will be generated. Transfer the completed executable file (hello) to a directory on μClinux that has an execution path through ftp or the like.

Application debugging

Next, I will show you how to remotely debug your application using “gdbserver” and Insight.

“gdbserver” spawns the debuggee program as a child process using the “vfork” system call. In addition, the "ptrace" system call is used to implement functions such as reading and writing registers and memory, and setting breakpoints.

The “gdbserver” source code is included in the “gdb” source package and must be built for each CPU architecture. For this reason, Next Dimension ported “gdbserver” for Nios II, which runs on μClinux, and built an application debugging environment.

In this porting, we mainly add and modify the following parts.

・Correction of ptrace.c in uClinux-dist

・Addition and modification of break_handler and exception_handler

・Development of CPU dependent part in gdbserver

・Modification of hardware such as deletion of JTAG_Debug module

See below for details. (http://www.next-dimension.co.jp/Nios2uClinux.html) Figure 9 shows the application debugging environment.

Figure 9 Application debug environment

First, execute the “gdbserver” command on μClinux with options for the IP address of the host PC, port number, and application to be debugged (“hello” here).

“gdbserver” spawns a “hello” process and stops it. After that, "gdbserver" waits for a connection from the host PC (debugger).

Next, launch Insight Debugger with the “nios2-elf-insight” command and open the “hello.gdb” file generated by the debug build. Start the “Target Selection” screen from “File ⇒ Target Setting”, set as follows, and click the Run button.

・target: “Remote/TCP”

・Hostname: <target IP address>

・Port: <Port number specified in nios2-gdb-server.exe>

・Uncheck More Option ⇒ Download Program

“gdbserver” and Insight Debugger are connected, and the program stops at the first line of the main function. Note that Linux does not know where the application will be loaded in memory, so the base address of the application is set during the connection process.

Figure 10 Application debug screen

Normally, the program is downloaded from the debugger, but when using "gdbserver", the process is already created by "gdbserver", so please note that the program will not be downloaded from the Insight Debugger. .

Application release build and run

Once you have finished debugging your application and are ready to incorporate it into your final product, you need to run a release build. The release build method is to build without the "-g" option added when running "nios2-linux-uclibc-gcc". Copy the generated executable file (hello) to the /bin directory of μClinux as described in the section "Application debug build and debug" and rebuild the kernel.

After starting μClinux, execute “hello” and if it works normally, the application development is finished. Figure 11 shows the execution result of “hello”.

Figure 11 Executing hello