Awesome
Build EAR
Bear is a tool that generates a compilation database for clang tooling.
The JSON compilation database is used in the clang project to provide information on how a single compilation unit is processed. With this, it is easy to re-run the compilation with alternate programs.
One way to get a compilation database is to use cmake
as the build
tool. Passing -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
to cmake generates
the compile_commands.json
file into the current directory.
For non-cmake projects, Bear generates the JSON file during the build process.
The concept behind Bear is: to execute the original build command and
intercept the exec
calls issued by the build tool. To achieve that,
Bear uses the LD_PRELOAD
or DYLD_INSERT_LIBRARIES
mechanisms provided
by the dynamic linker.
Bear has two components: the library and the binary. The library
redefines the exec
methods to be used by all child processes. The
executable enables the use of the library for child processes and
writes the output file.
How to build
Bear should be quite portable on UNIX operating systems. It has been tested on FreeBSD, GNU/Linux and OS X.
Prerequisites
- an ANSI C compiler, to compile the sources.
- cmake, to configure the build process.
- make, to run the build. The makefiles are generated by
cmake
. - python is a runtime dependency. The
bear
command is written in Python. (version >= 2.7) - lit is an optional dependency to run the functional tests
Build commands
Ideally, you should build Bear in a separate build directory.
cmake $BEAR_SOURCE_DIR
make all
make install # to install
make check # to run tests
make package # to make packages
You can configure the build process with passing arguments to cmake.
How to use
After installation the usage is like this:
bear make
The output file called compile_commands.json
found in current directory.
For more options you can check the man page or pass --help
parameter.
Known issues
Environment overriding caused problems
Because Bear uses LD_PRELOAD
or DYLD_INSERT_LIBRARIES
environment variables,
it does not append to it, but overrides it. So builds which are using these
variables might not work. (I don't know any build tool which does that, but
please let me know if you do.)
Build with multiple architecture support
Multilib is one of the solutions allowing users to run applications built for various application binary interfaces (ABIs) of the same architecture. The most common use of multilib is to run 32-bit applications on 64-bit kernel.
For OSX this is not an issue. The build commands from previous section will work, Bear will intercept compiler calls for 32-bit and 64-bit applications.
For Linux, a small tune is needed at build time. Need to compile libear.so
libray for 32-bit and for 64-bit too. Then install these libraries to the OS
preferred multilib directories. And replace the libear.so
path default
value with a single path, which matches both. (The match can be achieved by
the $LIB
token expansion from the dynamic loader. See man ld.so
for more.)
Debian derivatives are using lib/i386-linux-gnu
and lib/x86_64-linux-gnu
,
while many other distributions are simple lib
and lib64
. Here comes an
example build script to install a multilib capable Bear. It will install Bear
under /opt/bear
on a non Debian system.
(cd ~/build32; cmake "$BEAR_SOURCE_DIR" -DCMAKE_C_COMPILER_ARG1="-m32"; VERBOSE=1 make all;)
(cd ~/build64; cmake "$BEAR_SOURCE_DIR" -DCMAKE_C_COMPILER_ARG1="-m64" -DDEFAULT_PRELOAD_FILE='/opt/bear/$LIB/libear.so'; VERBOSE=1 make all;)
sudo install -m 0644 ~/build32/libear/libear.so /opt/bear/lib/libear.so
sudo install -m 0644 ~/build64/libear/libear.so /opt/bear/lib64/libear.so
sudo install -m 0555 ~/build64/bear/bear" /opt/bear/bin/bear
To check you installation, install lit
and run the test suite.
PATH=/opt/bear/bin:$PATH lit -v test
PATH=/opt/bear/bin:$PATH lit -v test -DMULTILIB=true
Empty compilation database on OS X Captain or Fedora
Security extension/modes on different operating systems might disable library
preloads. This case Bear behaves normally, but the result compilation database
will be empty. (Please make sure it's not the case when reporting bugs.)
Notable examples for enabled security modes are: OS X 10.11 (check with
csrutil status | grep 'System Integrity Protection'
), and Fedora, CentOS, RHEL
(check with sestatus | grep 'SELinux status'
).
Workaround could be to disable the security feature while running Bear. (This
might involve reboot of your computer, so might be heavy workaround.) Another
option if the build tool is not installed under certain directories.
Or use tools which are using compiler wrappers. (It injects a fake compiler
which does record the compiler invocation and calls the real compiler too.)
An example for such tool might be scan-build. The build system
shall respect CC
and CXX
environment variables.
Problem reports
If you find a bug in this documentation or elsewhere in the program or would like to propose an improvement, please use the project's github issue tracker. Please describing the bug and where you found it. If you have a suggestion how to fix it, include that as well. Patches are also welcome.