How can I pass git SHA1 to compiler as definition

Question

In a Makefile this would be done with something like:

g++ -DGIT_SHA1="`git log -1 | head -n 1`" ...

This is very useful, because the binary knows exact commit SHA1 so it can dump it in case of segfault.

How can I achieve the same with CMake?

Answer 1

It would be nice to have a solution that catches changes to the repository (from git describe --dirty), but only triggers recompilation if something about the git information has changed.

Some of the existing solutions:

1. Use 'execute_process'. This only gets the git information at configure time, and can miss changes to the repository.
2. Depend on .git/logs/HEAD. This only triggers recompilation when something in the repo changes, but misses the changes to get the '-dirty' state.
3. Use a custom command to rebuild the version information every time a build is run. This catches changes resulting in the -dirty state, but triggers a recompilation all the time (based on the updated timestamp of the version information file)

One fix to the third solution is to use the CMake 'copy_if_different' command, so the timestamp on the version information file only changes if the contents change.

The steps in the custom command are:

1. Collect the git information to a temporary file
2. Use 'copy_if_different' to copy the temporary file to the real file
3. Delete the temporary file, to trigger the custom command to run again on the next 'make'

The code (borrowing heavily from kralyk's solution):

# The 'real' git information file
SET(GITREV_BARE_FILE git-rev.h)
# The temporary git information file
SET(GITREV_BARE_TMP git-rev-tmp.h)
SET(GITREV_FILE ${CMAKE_BINARY_DIR}/${GITREV_BARE_FILE})
SET(GITREV_TMP ${CMAKE_BINARY_DIR}/${GITREV_BARE_TMP})

ADD_CUSTOM_COMMAND(
  OUTPUT ${GITREV_TMP}
  COMMAND ${CMAKE_COMMAND} -E echo_append "#define GIT_BRANCH_RAW " > ${GITREV_TMP}
  COMMAND ${GIT_EXECUTABLE} rev-parse --abbrev-ref HEAD >> ${GITREV_TMP}
  COMMAND ${CMAKE_COMMAND} -E echo_append "#define GIT_HASH_RAW " >> ${GITREV_TMP}
  COMMAND ${GIT_EXECUTABLE} describe --always --dirty --abbrev=40 --match="NoTagWithThisName" >> ${GITREV_TMP}
  COMMAND ${CMAKE_COMMAND} -E copy_if_different ${GITREV_TMP} ${GITREV_FILE}
  COMMAND ${CMAKE_COMMAND} -E remove ${GITREV_TMP}
  WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
  VERBATIM
)
# Finally, the temporary file should be added as a dependency to the target

ADD_EXECUTABLE(test source.cpp ${GITREV_TMP})

Answer 2

Here's my solution, which I think is reasonably short yet effective ;-)

First, a file is needed in the source tree (I name it git-rev.h.in), it should looks something like this:

#define STR_EXPAND(x) #x
#define STR(x) STR_EXPAND(x)
#define GIT_REV STR(GIT_REV_)
#define GIT_REV_ \ 
 

(Please never mind those macros, that's a little bit insane trick to make a string out of a raw value.) It is essential that this file has exactly one empty newline at the end so that value can be appended.

And now this code goes in respective CMakeLists.txt file:

# --- Git revision ---
add_dependencies(your_awesome_target gitrev)      #put name of your target here
include_directories(${CMAKE_CURRENT_BINARY_DIR})  #so that the include file is found
set(gitrev_in git-rev.h.in)                       #just filenames, feel free to change them...
set(gitrev git-rev.h)
add_custom_target(gitrev
  ${CMAKE_COMMAND} -E remove -f ${CMAKE_CURRENT_BINARY_DIR}/${gitrev}
  COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/${gitrev_in} ${CMAKE_CURRENT_BINARY_DIR}/${gitrev}
  COMMAND git rev-parse HEAD >> ${CMAKE_CURRENT_BINARY_DIR}/${gitrev}
  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}         #very important, otherwise git repo might not be found in shadow build
  VERBATIM                                              #portability wanted
)

This command ensuers that the git-rev.h.in is copied in the build tree as git-rev.h and git revision is appended at its end.

So all you need to do next is include git-rev.h in one of your files and do whatever you want with the GIT_REV macro, which yields current git revision hash as a string value.

The nice thing about this solution is that the git-rev.h is recreated each time you build the associated target, so you don't have to run cmake over and over again.

It also should be pretty portable - no non-portable external tools were used and even the bloody stupid windows cmd supports the > and >> operators ;-)

Answer 3

For a quick and dirty, possibly not portable way to get the git SHA-1 into a C or C++ project using CMake, I use this in CMakeLists.txt:

add_custom_target(git_revision.h
 git log -1 "--format=format:#define GIT_REVISION \"%H\"%n" HEAD > git_revision.h
 WORKING_DIRECTORY ${CMAKE_SOURCE_DIR} VERBATIM)

It assumes that CMAKE_SOURCE_DIR is part of a git repository, and that git is available on the system, and that an output redirection will be properly parsed by the shell.

You can then make this target a dependency of any other target using

add_dependencies(your_program git_revision.h)

Each time your_program is built, the Makefile (or other build system, if this works on other build systems) will recreate git_revision.h in the source directory, with the contents

#define GIT_REVISION "<SHA-1 of the current git revision>"

So you can #include git_revision.h from some source code file and use it that way. Note that the header is created at literally every build, i.e. even if every other object file is up to date, it will still run this command to recreate git_revision.h. I figure that shouldn't be a huge problem because usually you don't rebuild the same git revision over and over again, but it's something to be aware of, and if it is a problem for you, then don't use this. (It's probably possible to hack up a workaround using add_custom_command but I haven't needed it so far.)

Answer 4

I can't help you with the CMake side, but with respect to Git side I would recommend taking a look how Linux kernel and Git project itself does it, via GIT-VERSION-GEN script, or how tig does it in its Makefile, by using git describe if there is git repository present, falling back to "version" / "VERSION" / "GIT-VERSION-FILE" generated and present in tarballs, finally falling back to default value hardcoded in script (or Makefile).

The first part (using git describe) requires that you tag releases using annotated (and possibly GPG signed) tags. Or use git describe --tags to use also lightweight tags.

Answer 5

The following solution is based on the observation that Git updates the HEAD log whenever you pull or commit something. Note that e.g. Drew's suggestion above will update the Git information only if you rebuild the CMake cache manually after every commit.

I use a CMake "custom command" that generates a one-line header file ${SRCDIR}/gitrevision.hh where ${SRCDIR} is the root of your source tree. It will be re-made only when a new commit is made. Here is the necessary CMake magic with some comments:

# Generate gitrevision.hh if Git is available
# and the .git directory is present
# this is the case when the software is checked out from a Git repo
find_program(GIT_SCM git DOC "Git version control")
mark_as_advanced(GIT_SCM)
find_file(GITDIR NAMES .git PATHS ${CMAKE_SOURCE_DIR} NO_DEFAULT_PATH)
if (GIT_SCM AND GITDIR)
    # Create gitrevision.hh
    # that depends on the Git HEAD log
    add_custom_command(OUTPUT ${SRCDIR}/gitrevision.hh
        COMMAND ${CMAKE_COMMAND} -E echo_append "#define GITREVISION " > ${SRCDIR}/gitrevision.hh
        COMMAND ${GIT_SCM} log -1 "--pretty=format:%h %ai" >> ${SRCDIR}/gitrevision.hh
        DEPENDS ${GITDIR}/logs/HEAD
        VERBATIM
    )
else()
    # No version control
    # e.g. when the software is built from a source tarball
    # and gitrevision.hh is packaged with it but no Git is available
    message(STATUS "Will not remake ${SRCDIR}/gitrevision.hh")
endif()

The contents of gitrevision.hh will look like this:

#define GITREVISION cb93d53 2014-03-13 11:08:15 +0100

If you want to change this then edit the --pretty=format: specification accordingly. E.g. using %H instead of %h will print the full SHA1 digest. See the Git manual for details.

Making gitrevision.hh a fully-fledged C++ header file with include guards etc. is left as an exercise to the reader :-)

Answer 6

I'd use sth. like this in my CMakeLists.txt:

exec_program(
    "git"
    ${CMAKE_CURRENT_SOURCE_DIR}
    ARGS "describe"
    OUTPUT_VARIABLE VERSION )

string( REGEX MATCH "-g.*$" VERSION_SHA1 ${VERSION} )
string( REGEX REPLACE "[-g]" "" VERSION_SHA1 ${VERSION_SHA1} )

add_definitions( -DGIT_SHA1="${VERSION_SHA1}" )