April 23, 2015

Kernel development for OpenEmbedded with Eclipse

by Yuri Nenakhov

Eclipse with C Development Tool (CDT) is a very powerful and feature-rich IDE for developing embedded Linux applications, such as Elphel393 camera. CDT includes CODAN — static code analysis tool which helps user to track possible problems in his code without compiling it, and Code Indexer, giving an auto-complete and code navigating (F3) features. They work independently from compiler, thus parsing the code in the same manner as compiler does is essential for producing meaningful results. As project grows, the interconnections between its parts tend to become more and more complicated, and maintaining the congruency of code processing for compiler and CODAN/Code Indexer becomes a non-trivial task. In the Internet, the most frequent recommendation for users who wish to develop Linux kernel with Eclipse is to disable CODAN feature since messy false error markers make it practically unusable. The situation becomes even worse for developers using external build tools (such as OpenEmbedded’s BitBake) as CODAN relies on output of a CDT-integrated build system to find correct way of code parsing. Anyway, embedded Linux applications usually involve kernel development, so we’ll try to find a practical approach to get the power of CODAN and Code Indexer into our hands.


Preparing the source code

I assume Poky image build environment is already set up. More info can be found here.

Main source of analysis errors are incorrect include paths, large number of unused source files which don’t contribute to build and break the index by redefining already defined symbols, and additional parameters that don’t present in a code and are transmitted to compiler via '-D' and '-include' flags. We can get all this data from build output. This will require a specific BitBake recipe and a parser script (the script is written in Python).

In Elphel, we use a specially arranged project tree for kernel development — it allows us to plug developed drivers and patches to any kernel used by BitBake with a number of symlinks. Two sets of symlinks allow BitBake to “see” developed source files while compiling the kernel and Eclipse to “see” the main kernel source code. To create this project tree, navigate to poky/ and run:

git clone https://git.elphel.com/Elphel/linux-elphel.git

Required links are described in a kernel build recipe and created by BitBake during the ‘unpack’ task. Build is needed to produce all automatically generated header files.

. ./oe-init-build-env
bitbake linux-xlnx -c clean -f
bitbake linux-xlnx -c unpack -f
bitbake linux-xlnx -f

Setting up the Eclipse project
Created project tree already contains prepared project settings file (.cproject). If you’re interested in Linux development for Elphel393 camera, you can use it with a couple of easy initial steps described in README.md. If you’re interested in tuning your own project, I’ll give a summary of required settings in this blog.

Run Eclipse. Some additional heap memory may be required for indexing the kernel source:

./eclipse -vmargs -Xmx4G

  • File → New → C Project
    • Name = linux-elphel (this is hard-coded in a parser script so if you want to change it, edit the script as well)
    • Uncheck “Use default location”
    • Location = path to linux-elphel/ project directory
    • Project type = Makefile project → Empty Project
    • Toolchain = Linux GCC
    • [Next] → Advanced Settings (OK to overwrite)
  • C/C++ General → Preprocessor Include Paths → Entries → GNU C → CDT User Settings
    • [Add…] → Select “Preprocessor macros file” → linux/include/generated/autoconf.h → [OK]
    • [Add…] → Select “Preprocessor macros file” → linux/include/linux/compiler.h → [OK]
  • C/C++ General → Indexer
    • Check “Enable project specific setttings”
    • Check “Enable indexer”
    • Uncheck “Index source files not included in the build”
    • Uncheck “Index unused headers”
    • Check “Index header variants”
    • Uncheck “Index source and header files opened in editor”
    • Uncheck “Allow heuristic resolution of includes”
    • Set size of files to be skipped >100MB (effectively disabling this feature)
    • Uncheck all “Skip…” options
  • C/C++ General → Paths and symbols → Includes → GNU C → [Add…] → [Workspace] → /linux-elphel/linux/include → [OK] → [Ok]
  • C/C++ General → Paths and symbols → Source Location → [Add Folder…] → select linux/ → [OK]
    • In the same window delete default source location entry (/linux-elphel)
  • C/C++ General → Paths and symbols → Symbols → GNU C → [Add…] → Name=__GNUC__, value=4 → [OK]
  • C/C++ General → Preprocessor Include Paths → Providers → Uncheck all except CDT User Setting Entries and CDT Managed Build Setting Entries
  • [OK] to close Advanced Settings window → Finish.

The project is created. Close Eclipse for now.

Running the parser
You’ll need a modified recipe file and a parser script. To make BitBake output all the information required, add a variable assignment to the recipe:

EXTRA_OEMAKE = "${_MAKEFLAGS}"

Download the parser script into poky/build/ directory:

git clone https://git.elphel.com/Elphel/kernel-bitbake-parser.git

This script is heavily dependent on the project structure and has to be customized for your project. Feel free to ask if you have any questions about it. Build kernel with specific set of flags (it’ll take a while) and parse the output:

export _MAKEFLAGS="-s -w -j1 -B KCFLAGS='-v'"
export BB_ENV_EXTRAWHITE="$BB_ENV_EXTRAWHITE _MAKEFLAGS"
bitbake linux-xlnx -c clean -f
bitbake linux-xlnx -c compile -v -f|python3 ./kernel-bitbake-parser/kbparse.py

The output consists of 4 sections — Define statements, Include paths, Source paths and Extra include files. First 3 of them are formatted as XML tags allowing to copy’n’paste them directly into respective nodes of a .cproject file. Script will attempt to automatically modify .cproject file as well. Extra includes have to be manually added from Eclipse. (C/C++ General → Preprocessor Include Paths → Entries → GNU C → CDT User Settings → [Add…] → Select “Include file” → Copy the path from parser output → [OK])

Run Eclipse:

./eclipse -vmargs -Xmx4G

Project → C/C++ Index → Rebuild.

The result is less than 0.005% of unresolved symbols (this can be seen from the Error Log, Window → Show view → Other… → Error Log) and no error markers from CODAN.


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