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Create x-compile_commands

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Overview

When cross-compiling for example with a Yocto sdk, most of the time we are using some kind of gcc with different flags. The flags are set when sourcing the environment script, and is stuck during the session. This is all fine, unfortunately this setup makes it hard to use any clang-tools which are available, which are great for both verification and for formatting code and many other things. Most of the time the clang tools (e.g clang-tidy ) needs to be able to read the compile_commands.json file, to be able perform its task. The compile_commands file as its name suggests consists of commands how the project-files are compiled into object code for each translation unit. The compile_commands.json can be generated in many different way (e.g cmake, bear …), but for this exercises I will stick to using cmake with the build command -DCMAKE_EXPORT_COMPILE_COMMANDS=1 which will generate a compile_commands.json in the build directory. This document will try to explain how to generate a compile_commands.json switching out the arm-gcc with clang and provide and exclude flags which are not synchronized between clang and gcc. I will be using only c++, the same should work for c. Lets dive right into it.

Building, generating compile_commands.json

The first task would be to setup the environment for cross-compiling by sourcing the yocto-environment.

source /opt/ocp/13.4.1/environment-setup-cortexa7t2hf-neon-poky-linux-gnueabi

We can now inspect the CXX and CXXFLAGS in the environment. This will be useful later on.

echo $CXX
arm-poky-linux-gnueabi-g++ -march=armv7ve -mthumb -mfpu=neon \
-mfloat-abi=hard -mcpu=cortex-a7 \
--sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi
echo $CXXFLAGS
-O2 -pipe -g -feliminate-unused-debug-types

Then its time start building the project with cmake but provide the generation of compile_commands e.g

cd src/project && mkdir build && cd build
cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=1 ..
.
.
.
.

This will generate the auxiliary cmake files and cache together with the make and compile_commands.json.

Compile commands

If we start inspecting the compile_commands.json we notice that its a json list with a structure. .eg

[
    {
        "directory": "/home/ocp/src/cpp1/darf/build/src/service",
        "command": "arm-poky-linux-gnueabi -march=armv7ve....... -std=gnu++17 -o main.cpp.o -c main.cpp",
        "file": "/home/ocp/src/cpp1/darf/src/service/main.cpp"
  }
]

If you want to parse the structure you can always use the quicktype excellent code generation for json structures. But for this exercise its not necessary.

Trying it out

The first task is to see what happens if we just grab one of the compile commands from the file and just replace the compiler (arm-poky-linux-gnueabi) with clang++ and see what happens So from the compile_commands.json I grab one command,

CMD="/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi  -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include   -O2 -pipe -g -feliminate-unused-debug-types  -Wno-psabi -Wno-maybe-uninitialized   -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
compile=$(echo ${CMD} | sed s#/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++#clang++#)
echo ${compile}

OK, if we run this we get

eval ${compile}
clang: warning: argument unused during compilation: '-mthumb' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-mfpu=neon' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-mfloat-abi=hard' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-mcpu=cortex-a7' [-Wunused-command-line-argument]
warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option]
warning: unknown warning option '-Wno-maybe-uninitialized'; did you mean
      '-Wno-uninitialized'? [-Wunknown-warning-option]
error: unknown target CPU 'armv7ve'
note: valid target CPU values are: nocona, core2, penryn, bonnell, atom, silvermont, slm,
      goldmont, goldmont-plus, tremont, nehalem, corei7, westmere, sandybridge, corei7-avx,
      ivybridge, core-avx-i, haswell, core-avx2, broadwell, skylake, skylake-avx512, skx,
      cascadelake, cannonlake, icelake-client, icelake-server, knl, knm, k8, athlon64,
      athlon-fx, opteron, k8-sse3, athlon64-sse3, opteron-sse3, amdfam10, barcelona, btver1,
      btver2, bdver1, bdver2, bdver3, bdver4, znver1, x86-64

If we ignore the warnings for the time being and focus on the errors, we can see that there is something wrong with specifying the target architecture. The problem is that clang is using different flags to get this to work, what we need is the clang version of cross-compiling. This information can be found at clang cross compile web site. So instead of using the -march... we need to provide the clang triple which in my case is --target=armv7e-unknown-linux-elf

So lets replace the -march=armv7ve flag with clangs equivalent (--target=armv7e-unknown-linux-elf)

CMD="/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi  -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include   -O2 -pipe -g -feliminate-unused-debug-types  -Wno-psabi -Wno-maybe-uninitialized   -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
compile=$(echo ${CMD} | sed s#/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++#clang++#)
compile=$(echo ${compile} | sed s/-march=armv7ve/--target=armv7e-unknown-linux-elf/)
echo ${compile}

Now the output file is not really what I want so will replace that with something better.

So lets extend the substitution.

CMD="/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi  -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include   -O2 -pipe -g -feliminate-unused-debug-types  -Wno-psabi -Wno-maybe-uninitialized   -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
compile=$(echo ${CMD} | sed s#/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++#clang++#)
compile=$(echo ${compile} | sed -e 's/-march=armv7ve/--target=armv7e-unknown-linux-elf/' -e 's/-o.*.cpp.o /-o test.o /' )
echo $compile

and if we now run the compile command we get

eval $compile
warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option]
warning: unknown warning option '-Wno-maybe-uninitialized'; did you mean
      '-Wno-uninitialized'? [-Wunknown-warning-option]
In file included from /home/ocp/src/cpp1/eden/src/adam/src/main.cpp:3:
In file included from /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/boost/asio.hpp:20:
In file included from /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/boost/asio/async_result.hpp:18:
In file included from /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/boost/asio/detail/config.hpp:26:
In file included from /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/boost/config.hpp:44:
/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/boost/config/select_stdlib_config.hpp:18:12: fatal error: 
      'cstddef' file not found
#  include <cstddef>
           ^~~~~~~~~
2 warnings and 1 error generated.

This is what we wanted, we almost got it to work, we are still having some warnings, but we will fix them. We could not find the system includes, so we need to add them. But lets first check out the warnings.

Fix Warnings

Ok we still have some warnings that needs to be handled. We start with the -Wno-psabi which seems to be a flag that is not supported in clang, the -Wno-maybe-uninitialized also seems to be a warning that is not supported by clang. So lets remove them both.

CMD="/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi  -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include   -O2 -pipe -g -feliminate-unused-debug-types  -Wno-psabi -Wno-maybe-uninitialized   -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
compile=$(echo ${CMD} | sed s#/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++#clang++#)
compile=$(echo ${compile} | sed -e \
's/-march=armv7ve/--target=armv7e-unknown-linux-elf/' \
-e 's/-o.*.cpp.o /-o test.o /' \
-e 's/-Wno-psabi//' \
-e 's/-Wno-maybe-uninitialized//')
echo $compile

and running the command now results in

eval $compile
In file included from /home/ocp/src/cpp1/eden/src/adam/src/main.cpp:3:
.
.
.
.
/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/boost/config/select_stdlib_config.hpp:18:12: fatal error: 
      'cstddef' file not found
#  include <cstddef>
           ^~~~~~~~~
1 error generated.

Finally! no errors or warnings, but we still have an issue with the include files. So lets figure that one out.

Finding includes

as we saw in the previous section we are missing the system paths, these needs to be the same as when we ran the arm-poky-linux-gnueabi. One way to find out which they are is to compile with syntax-only flag, which basically compiles without output.

eval $CXX -v -std=c++17 -xc++ -fsyntax-only /dev/null

This outputs quite a bit of information but we are just interested in the system include paths, these can be figured out by checking between the lines

#include <...> search starts here:
.
.
.  
.
.
End of search list.

So lets construct something that takes out these include directories. Unfortunately the eval-command will print to stderr which is a bit of a hassle and we need to be able to extract the include directories, and discard all the other output. This might be a bit wild, but I will try to explain each of the rows and try to explain what it does.

EPA=$( { eval $CXX -v -std=c++17 -xc++ -fsyntax-only /dev/null; } 2>&1 )
echo ${EPA} | \
    sed -E -n -e '/<...>/,/End/p' | \
    sed -E -e 's/^End.*$//' \
        -e 's/^.*<...>.*$//' \
        -e 's/^\s*//' \
        -e '/^\s*$/d' | \
    awk 'BEGIN{print "include_directories(SYSTEM"} \
                     {print "    \"" $0 "\"" } \
         END{print")"}'

line 1
This line will output both stdin and stderr to the variable. The curly braces are used for output grouping, where the 2>&1 indicates that both the stdin and stderr should be outputted to the variable.
line 3
This little neat trick is Ranges by pattern it only includes the line between the two regexp. e.g
sed '/<regexp Begin>/,/<Regexp End>/p'

That means we are picking out the lines between <...> and ^End

line 4,5

Now piping the output from the previous range pattern we have to remove the End and the Begin (<..>) since those are included. One might do this with another range , e.g combining line number and range. .eg

echo $EPA | sed -n  '/<...>/,/End/p' | sed  -n '2,/^End/p' | sed '/^End/d'
line 6
Extending the sed expression, we now remove the white space from the beginning of every row.
line 7
And finally removes the lines without anything.
line 8
finally we create an awk expression that prints out the content as a cmake file.

The output of this expression would be:

include_directories(SYSTEM
    "/usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8"
    "/usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8"
    "/usr/bin/../lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward"
    "/usr/include/clang/8.0.1/include"
    "/usr/local/include"
    "/usr/include/x86_64-linux-gnu"
    "/usr/include"
)

If we redirect the output to a cmake file e.g clang-compile, we can then include that file into our own project cmake file.

Building the first clang++ object.

If we now start to wrap things up , we can use both of the above methods to construct a command which hopefully build a complete object.

Lets start with creating a compile command (see Fix warnings).

CMD="/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include   -O2 -pipe -g -feliminate-unused-debug-types  -Wno-psabi -Wno-maybe-uninitialized   -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
compile=$(echo ${CMD} | sed s#/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++#clang++#)
compile=$(echo ${compile} | sed -e \
's/-march=armv7ve/--target=armv7e-unknown-linux-elf/' \
-e 's/-o.*.cpp.o /-o test.o /' \
-e 's/-Wno-psabi//' \
-e 's/-Wno-maybe-uninitialized//')
echo $compile

We need to include the paths for the $compile command

EPA=$( { eval $CXX -v -std=c++17 -xc++ -fsyntax-only /dev/null; } 2>&1 )
includes=$(echo ${EPA} | \
    sed -E -n -e '/<...>/,/End/p' | \
    sed -E -e 's/^End.*$//' \
        -e 's/^.*<...>.*$//' \
        -e 's/^\s*//' \
        -e '/^\s*$/d' | \
        awk '{print " -isystem " $0}' | \
        tr -d '\n')

I removed the cmake output from the awk expression and added isystem instead , and the last pipe will remove the new lines, since otherwise each of the lines would be seen as a command in bash.

So the final output

CMD="/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++   -march=armv7ve -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include   -O2 -pipe -g -feliminate-unused-debug-types  -Wno-psabi -Wno-maybe-uninitialized   -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
compile=$(echo ${CMD} | sed s#/opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-g++#clang++#)
compile=$(echo ${compile} | sed -e \
                                's/-march=armv7ve/--target=armv7e-unknown-linux-elf/' \
                                -e 's/-o.*.cpp.o /-o test.o /' \
                                -e 's/-Wno-psabi//' \
                                -e 's/-Wno-maybe-uninitialized//')

EPA=$( { eval $CXX -v -std=c++17 -xc++ -fsyntax-only /dev/null; } 2>&1 )
includes=$(echo ${EPA} | \
               sed -E -n -e '/<...>/,/End/p' | \
               sed -E -e 's/^End.*$//' \
                   -e 's/^.*<...>.*$//' \
                   -e 's/^\s*//' \
                   -e '/^\s*$/d' | \
               awk '{print " -isystem " $0}' | \
               tr -d '\n')

echo $compile $includes
eval $compile $includes

This will construct and create the object code using clang++.

Building a complete project

In the previous section we built an object using clang++, but what about building a complete project? This section, will show how to build the project. Even though each and every translation unit will be compiled into a object file, the complete project will end up failing due to that linking together the object files will fail.

Lets start with creating a the cmake file with the system includes that is needed, from the expression show here we just output the result to a file as the following expression shows. The output file is created in the project root directory

EPA=$( { eval $CXX -v -std=c++17 -xc++ -fsyntax-only /dev/null; } 2>&1 )
echo ${EPA} | \
    sed -E -n -e '/<...>/,/End/p' | \
    sed -E -e 's/^End.*$//' \
        -e 's/^.*<...>.*$//' \
        -e 's/^\s*//' \
        -e '/^\s*$/d' | \
    awk 'BEGIN{print "include_directories(SYSTEM"} \
                     {print "    \"" $0 "\"" } \
         END{print")"}' > clang_sys_includes.cmake

Next part is removing the flags which are not wanted , we did that in Fix Warning section. But since we are using cmake we need another way of removing the flags. We already identified the flags, all we need to do now is to remove those flags, and that can be done easily in the cmake and string replace.

cat >> clang_sys_includes.cmake <<EOF
string(REPLACE "-Wno-psabi" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
string(REPLACE "-Wno-maybe-uninitialized" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
EOF

If we now include this file into our root CMakeLists.txt e.g

  cmake_minimum_required(VERSION 3.11)
  include(clang_sys_includes)
.
.
.

If for some reason you set the CXX_FLAGS somewhere in you cmake files. Make sure that the include is added afterwards, otherwise it might overwrite the changes we made.

The next part is to actually run the cmake from a build directory. I just created a build_clang directory and ran this command.

CXX="clang++ --target=armv7e-unknown-linux-elf \
-mthumb \                                                           
-mfpu=neon \
-mfloat-abi=hard \
-mcpu=cortex-a7" \
cmake ..

This will unfortunately not work. The reason is that cmake will try to build a small program to test the compiler, and since the linker is not working properly it will fail. But there is a way of getting away from this error, and that is to override the test.

CXX="clang++ --target=armv7e-unknown-linux-elf \
-mthumb \
-mfpu=neon \
-mfloat-abi=hard \
-mcpu=cortex-a7" \
cmake -DCMAKE_CXX_COMPILER_WORKS=1 -DCMAKE_EXPORT_COMPILE_COMMANDS=1 ..

And finally we have got cmake to pass through the build. We could not open compile_commands.json and check the content.

[
{
  "directory": "/home/ocp/src/cpp1/eden/build_clang/src/adam",
  "command": "/usr/bin/clang++  --target=armv7e-unknown-linux-elf -mthumb -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a7 --sysroot=/opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi  -DBOOST_ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION -DBOOST_ENABLE_ASSERT_HANDLER -I/home/ocp/src/cpp1/eden/include -I/home/ocp/src/cpp1/eden/src/adam/include -I/home/ocp/src/cpp1/eden/src/serpent/include -I/home/ocp/user_sysroots/13.4.1/usr/include -I/home/ocp/src/cpp1/eden/gen_files -I/home/ocp/src/cpp1/eden/src/adam/../include -isystem /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/c++/8.2.0 -isystem /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/c++/8.2.0/arm-poky-linux-gnueabi -isystem /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/include/c++/8.2.0/backward -isystem /opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/lib/arm-poky-linux-gnueabi/gcc/arm-poky-linux-gnueabi/8.2.0/include -isystem /opt/ocp/13.4.1/sysroots/cortexa7t2hf-neon-poky-linux-gnueabi/usr/lib/gcc/arm-poky-linux-gnueabi/8.2.0/include -isystem /opt/ocp/13.4.1/sysroots/x86_64-ocpsdk-linux/usr/lib/arm-poky-linux-gnueabi/gcc/arm-poky-linux-gnueabi/8.2.0/include-fixed    -Wall -Wextra -pedantic -funsigned-char -std=gnu++17 -o CMakeFiles/adam_app.dir/src/main.cpp.o -c /home/ocp/src/cpp1/eden/src/adam/src/main.cpp",
  "file": "/home/ocp/src/cpp1/eden/src/adam/src/main.cpp"
},
.
.
.
]

Finally we have a compile_command.json which the clang tools understands. We can notice that the flags are removed and that the isystem is include. Now what happens if we actually run the build command on it?

/usr/bin/ld: unrecognised emulation mode: armelf_linux_eabi
Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 elf_iamcu i386linux elf_l1om elf_k1om i386pep i386pe
clang: error: linker command failed with exit code 1 (use -v to see invocation)
.
.
.

That was kind of expected, its able to build the object files. But the linker fails.

Date: 2019-10-04 Fri 09:02

Author: calle

Created: 2019-10-15 Tue 11:56

Validate