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Wataru Ashihara
Wataru Ashihara

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Create compilation database (compile_commands.json) for NetBSD-kernel source

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にほんご

Source code structure of NetBSD kernel (netbsd-src/sys/) is so complicated that it is almost impossible for a static-source-analysis tool to provide an accurate location of a symbol. For an example, cscope can't understand where <machine/endian.h> is:

  • sys/arch/hpc/stand/include/machine/endian.h?
  • or sys/arch/hpcmips/stand/include/machine/endian.h?

Actually it's ${OBJDIR}/sys/arch/amd64/compile/GENERIC/machine/endian.h! cscope doesn't know that the compilation is done in ${OBJDIR}/sys/arch/amd64/compile/GENERIC with the -I. flag.

To realize an accurate code analysis, compiling information is needed -- so-called compilation database or compile_commands.json.

Here's how to create compile_commands.json for NetBSD kernel on Linux (Ubuntu 18.04):
(I'll write additional information when it's done on NetBSD and macOS soon... NetBSD may be faceed with an issue in bear. And it's may be avoided by using scan-build)



# https://github.com/rizsotto/Bear/
sudo apt install bear

cd netbsd-src/

# First, create ${OBJDIR}/sys/arch/amd64/compile/GENERIC/Makefile
# and confirm that the kernel can be built
./build.sh kernel=GENERIC

cd ${OBJDIR}/sys/arch/amd64/compile/GENERIC/
${TOOLDIR}/bin/nbmake-amd64 clean
bear ${TOOLDIR}/bin/nbmake-amd64             # creates compile_commands.json
mv compile_commands.json ${NETBSD-SRC}/sys/  # optional


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Then open the kernel sources with your preferred editor that supports compilation database, such like vim with YouCompleteMe or CLion (used in this article). You may get errors from cc:



Compiler exited with error code 1: /usr/bin/cc -xc -c -mcmodel=kernel (snip) -v -dD -E
    Using built-in specs.
    (snip)
    End of search list.
    cc1: error: code model kernel does not support PIC mode


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The editor executes /usr/bin/cc for the code analysis, whereas it's should be ${TOOLDIR}/bin/x86_64--netbsd-gcc[--<target>] This problem can be resolved by simply replacing the path to the compiler:



cp compile_commands.json compile_commands.json.bak
sed -i s!'"cc",'!'"/home/wsh/src/netbsd/tools/bin/x86_64--netbsd-gcc",'!g compile_commands.json


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Enjoy code jumping!

For maintainers of official documentations

I'd be glad to migrate all or part of this and other articles to official documentations. Please make a comment here or contact me to do so.

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