3.7. Using GDB Server for Debugging
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## 3.7. Using GDB Server for Debugging

The GDB server utility provided with Sourcery G++ Lite can be used to debug a GNU/Linux application. While Sourcery G++ runs on your host system, `gdbserver` and the target application run on your target system. Even though Sourcery G++ and your application run on different systems, the debugging experience when using `gdbserver` is very similar to debugging a native application.

### 3.7.1. Running GDB Server

The GDB server executables are included in the sysroot in ABI-specific subdirectories of ``sysroot`/usr`. Use the executable from the sysroot and library subdirectory that match your program. See Section 3.2, “Library Configurations” for details.

You must copy the sysroot to your target system as described in Section 3.6.1, “Installing the Sysroot”. You must also copy the executable you want to debug to your target system.

If you have installed the sysroot in the root directory of the filesystem on the target, you can invoke `gdbserver` as:

    > gdbserver :10000 program arg1 arg2 ...

where `program` is the path to the program you want to debug and `arg1 arg2 ...` are the arguments you want to pass to it. The `:10000` argument indicates that `gdbserver` should listen for connections from GDB on port 10000. You can use a different port, if you prefer.

If you have installed the sysroot in an alternate directory, invoking `gdbserver` becomes more complicated. You must build your application using the link-time options to specify the location of the sysroot, as described in Section 3.6.2, “Using Linker Options to Specify the Sysroot Location”. You must also invoke `gdbserver` itself using the dynamic linker provided in the Sourcery G++ sysroot, as described in Section 3.6.3, “Specifying the Sysroot Location at Runtime”. In other words, the command to invoke `gdbserver` in this case would be similar to:

    > sysroot/lib/ld-linux.so.3 \
      --library-path sysroot/lib:sysroot/usr/lib \
      sysroot/usr/lib/bin/gdbserver :10000 program arg1 arg2 ...

### 3.7.2. Connecting to GDB Server from the Debugger

You can connect to GDB server by using the following command from within GDB:

    (gdb) target remote target:10000

where `target` is the host name or IP address of your target system.

When your program exits, `gdbserver` exits too. If you want to debug the program again, you must restart `gdbserver` on the target. Then, in GDB, reissue the `target` command shown above.

### 3.7.3. Setting the Sysroot in the Debugger

In order to debug shared libraries, GDB needs to map the pathnames of shared libraries on the target to the pathnames of equivalent files on the host system. Debugging of multi-threaded applications also depends on correctly locating copies of the libraries provided in the sysroot on the host system.

In some situations, the target pathnames are valid on the host system. Otherwise, you must tell GDB how to map target pathnames onto the equivalent host pathnames.

In the general case, there are two GDB commands required to set up the mapping:

    (gdb) set sysroot-on-target target-pathname
    (gdb) set sysroot host-pathname

This causes GDB to replace all instances of the `target-pathname` prefix in shared library pathnames reported by the target with `host-pathname` to get the location of the equivalent library on the host.

If you have installed the sysroot in the root filesystem on the target, you can omit the `set sysroot-on-target` command, and use only `set sysroot` to specify the location on the host system.

Refer to Section 3.6.1, “Installing the Sysroot” for more information about installing the sysroot on the target. Note that if you have installed a stripped copy of the provided libraries on the target, you should give GDB the location of an unstripped copy on the host.

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