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diff --git a/BUILD.md b/BUILD.md deleted file mode 100644 index 83f7e994..00000000 --- a/BUILD.md +++ /dev/null @@ -1,365 +0,0 @@ -<!-- -title: "The build system" -custom_edit_url: https://github.com/netdata/netdata/edit/master/BUILD.md ---> - -# The build system - -We are currently migrating from `autotools` to `CMake` as a build-system. This document -currently describes how we intend to perform this migration, and will be updated after -the migration to explain how the new `CMake` configuration works. - -## Stages during the build - -1. The `netdata-installer.sh`, take in arguments and environment settings to control the - build. -2. The configure step: `autoreconf -ivf ; ./configure` passing arguments into the configure - script. This becomes `generation-time` in CMake. This includes package / system detection - and configuration resulting in the `config.h` in the source root. -3. The build step: recurse through the generated Makefiles and build the executable. -4. The first install step: calls `make install` to handle all the install steps put into - the Makefiles by the configure step (puts binaries / libraries / config into target - tree structure). -5. The second install step: the rest of the installer after the make install handles - system-level configuration (privilege setting, user / groups, fetch/build/install `go.d` - plugins, telemetry, installing service for startup, uninstaller, auto-updates. - -The ideal migration result is to replace all of this with the following steps: -``` -mkdir build ; cd build ; cmake .. -D... ; cmake --build . --target install -``` - -The `-D...` indicates where the command-line arguments for configuration are passed into -`CMake`. - -## CMake generation time - -At generation time we need to solve the following issues: - -### Feature flags - -Every command-line switch on the installer and the configure script needs to becomes an -argument to the CMake generation, we can do this with variables in the CMake cache: - -CMakeLists.txt: -``` -option(ENABLE_DBENGINE "Enable the dbengine storage" ON) -... -if(${ENABLE_DBENGINE}) -... -endif() -``` - -Command-line interface -``` -cmake -DENABLE_DBENGINE -``` - -### Dependency detection - -We have a mixture of soft- and hard-dependencies on libraries. For most of these we expect -`pkg-config` information, for some we manually probe for libraries and include files. We -should treat all of the external dependencies consistently: - -1. Default to autodetect using `pkg-config` (e.g. the standard `jemalloc` drops a `.pc` - into the system but we do not check for it. -2. If no `.pc` is found perform a manual search for libraries under known names, and - check for accessible symbols inside them. -3. Check that include paths work. -4. Allow a command-line override (e.g. `-DWITH_JEMALLOC=/...`). -5. If none of the above work then fail the install if the dependency is hard, otherwise - indicate it is not present in the `config.h`. - -Before doing any dependency detection we need to determine which search paths are -really in use for the current compiler, after the `project` declaration we can use: -``` -execute_process(COMMAND ${CMAKE_C_COMPILER} "--print-search-dirs" - COMMAND grep "^libraries:" - COMMAND sed "s/^libraries: =//" - COMMAND tr ":" " " - COMMAND tr -d "\n" - OUTPUT_VARIABLE CC_SEARCH_DIRS - RESULTS_VARIABLE CC_SEARCH_RES) -string(REGEX MATCH "^[0-9]+" CC_SEARCH_RES ${CC_SEARCH_RES}) -#string(STRIP "${CC_SEARCH_RES}" CC_SEARCH_RES) -if(0 LESS ${CC_SEARCH_RES}) - message(STATUS "Warning - cannot determine standard compiler library paths") - # Note: we will probably need a different method for Windows... -endif() - -``` - -The output format for this switch works on both `Clang` and `gcc`, it also includes -the include search path, which can be extracted in a similar way. Standard advice here -is to list the `ldconfig` cache or use the `-V` flag to check, but this does not work -consistently across platforms - in particular `gcc` will reconfigure `ld` when it is -called to gcc's internal view of search paths. During experiments each of these -alternative missed / added unused paths. Dumping the compiler's own estimate of the -search paths seems to work consistently across clang/gcc/linux/freebsd configurations. - -The default behaviour in CMake is to search across predefined paths (e.g. `CMAKE_LIBRARY_PATH`) -that are based on heuristics about the current platform. Most projects using CMake seem -to overwrite this with their own estimates. - -We can use the extracted paths as a base, add our own heuristics based on OS and then -`set(CMAKE_LIBRARY_PATH ${OUR_OWN_LIB_SEARCH})` to get the best results. Roughly we do -the following for each external dependency: -``` -set(WITH_JSONC "Detect" CACHE STRING "Manually set the path to a json-c installation") -... -if(${WITH_JSONC} STREQUAL "Detect") - pkg_check_modules(JSONC json-c) # Don't set the REQUIRED flag - if(JSONC_FOUND) - message(STATUS "libjsonc found through .pc -> ${JSONC_CFLAGS_OTHER} ${JSONC_LIBRARIES}") - # ... setup using JSONC_CFLAGS_OTHER JSONC_LIBRARIES and JSONC_INCLUDE_DIRS - else() - find_library(LIB_JSONC - NAMES json-c libjson-c - PATHS ${CMAKE_LIBRARY_PATH}) # Includes our additions by this point - if(${LIB_JSONC} STREQUAL "LIB_JSONC-NOTFOUND") - message(STATUS "Library json-c not installed, disabling") - else() - check_library_exists(${LIB_JSONC} json_object_get_type "" HAVE_JSONC) - # ... setup using heuristics for CFLAGS and check include files are available - endif() - endif() -else() - # ... use explicit path as base to check for library and includes ... -endif() - -``` - -For checking the include path we have two options, if we overwrite the `CMAKE_`... variables -to change the internal search path we can use: -``` -CHECK_INCLUDE_FILE(json/json.h HAVE_JSONC_H) -``` -Or we can build a custom search path and then use: -``` -find_file(HAVE_JSONC_H json/json.h PATHS ${OUR_INCLUDE_PATHS}) -``` - -Note: we may have cases where there is no `.pc` but we have access to a `.cmake` (e.g. AWS SDK, mongodb,cmocka) - these need to be checked / pulled inside the repo while building a prototype. - -### Compiler compatibility checks - -In CMakeLists.txt: - -``` -CHECK_INCLUDE_FILE(sys/prctl.h HAVE_PRCTL_H) -configure_file(cmake/config.in config.h) -``` - -In cmake/config.in: - -``` -#cmakedefine HAVE_PRCTL_H 1 -``` - -If we want to check explicitly if something compiles (e.g. the accept4 check, or the -`strerror_r` typing issue) then we set the `CMAKE_`... paths and then use: -``` -check_c_source_compiles( - " - #include <string.h> - int main() { char x = *strerror_r(0, &x, sizeof(x)); return 0; } - " - STRERROR_R_CHAR_P) - -``` -This produces a bool that we can use inside CMake or propagate into the `config.h`. - -We can handle the atomic checks with: -``` -check_c_source_compiles( - " - int main (int argc, char **argv) - { - volatile unsigned long ul1 = 1, ul2 = 0, ul3 = 2; - __atomic_load_n(&ul1, __ATOMIC_SEQ_CST); - __atomic_compare_exchange(&ul1, &ul2, &ul3, 1, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); - __atomic_fetch_add(&ul1, 1, __ATOMIC_SEQ_CST); - __atomic_fetch_sub(&ul3, 1, __ATOMIC_SEQ_CST); - __atomic_or_fetch(&ul1, ul2, __ATOMIC_SEQ_CST); - __atomic_and_fetch(&ul1, ul2, __ATOMIC_SEQ_CST); - volatile unsigned long long ull1 = 1, ull2 = 0, ull3 = 2; - __atomic_load_n(&ull1, __ATOMIC_SEQ_CST); - __atomic_compare_exchange(&ull1, &ull2, &ull3, 1, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); - __atomic_fetch_add(&ull1, 1, __ATOMIC_SEQ_CST); - __atomic_fetch_sub(&ull3, 1, __ATOMIC_SEQ_CST); - __atomic_or_fetch(&ull1, ull2, __ATOMIC_SEQ_CST); - __atomic_and_fetch(&ull1, ull2, __ATOMIC_SEQ_CST); - return 0; - } - " - HAVE_C__ATOMIC) -``` - -For the specific problem of getting the correct type signature in log.c for the `strerror_r` -calls we can replicate what we have now, or we can delete this code completely and use a -better solution that is documented [here](http://www.club.cc.cmu.edu/~cmccabe/blog_strerror.html). -To replicate what we have now: -``` -check_c_source_compiles( - " - #include <string.h> - int main() { char x = *strerror_r(0, &x, sizeof(x)); return 0; } - " - STRERROR_R_CHAR_P) - -check_c_source_compiles( - " - #include <string.h> - int main() { int x = strerror_r(0, &x, sizeof(x)); return 0; } - " - STRERROR_R_INT) - -if("${STRERROR_R_CHAR_P}" OR "${STRERROR_R_INT}") - set(HAVE_DECL_STRERROR_R 1) -endif() -message(STATUS "Result was ${HAVE_DECL_STRERROR_R}") - -``` - -Note: I did not find an explicit way to select compiler when both `clang` and `gcc` are -present. We might have an implicit way (like redirecting `cc`) but we should put one in. - - - -### Debugging problems in test compilations - -Test compilations attempt to feed a test-input into the targeted compiler and result -in a yes/no decision, this is similar to `AC_LANG_SOURCE(.... if test $ac_...` in .`m4`. -We have two techniques to use in CMake: -``` -cmake_minimum_required(VERSION 3.1.0) -include(CheckCCompilerFlag) -project(empty C) - -check_c_source_compiles( - " - #include <string.h> - int main() { char x = *strerror_r(0, &x, sizeof(x)); return 0; } - " - STRERROR_R_CHAR_P) - -try_compile(HAVE_JEMALLOC ${CMAKE_CURRENT_BINARY_DIR} - ${CMAKE_CURRENT_SOURCE_DIR}/quickdemo.c - LINK_LIBRARIES jemalloc) -``` - -The `check_c_source_compiles` is light-weight: - -* Inline source for the test, easy to follow. -* Build errors are reported in `CMakeFiles/CMakeErrors.log` - -But we cannot alter the include-paths / library-paths / compiler-flags specifically for -the test without overwriting the current CMake settings. The alternative approach is -slightly more heavy-weight: - -* Can't inline source for `try_compile` - it requires a `.c` file in the tree. -* Build errors are not shown, the recovery process for them is somewhat difficult. - -``` -rm -rf * && cmake .. --debug-trycompile -grep jemal CMakeFiles/CMakeTmp/CMakeFiles/*dir/* -cd CMakeFiles/CMakeTmp/CMakeFiles/cmTC_d6f0e.dir # for example -cmake --build ../.. -``` - -This implies that we can do this to diagnose problems / develop test-programs, but we -have to make them *bullet-proof* as we cannot expose this to end-users. This means that -the results of the compilation must be *crisp* - exactly yes/no if the feature we are -testing is supported. - -### System configuration checks - -For any system configuration checks that fall outside of the above scope (includes, libraries, -packages, test-compilation checks) we have a fall-back that we can use to glue any holes -that we need, e.g. to pull out the packaging strings, inside the `CMakeLists.h`: -``` -execute_process(COMMAND cat ${CMAKE_CURRENT_SOURCE_DIR}/packaging/version - COMMAND tr -d '\n' - OUTPUT_VARIABLE VERSION_FROM_FILE) -message(STATUS "Packaging version ${VERSION_FROM_FILE}") -``` -and this in the `config.h.in`: -``` -#define VERSION_FROM_FILE "@VERSION_FROM_FILE@" -``` - -## CMake build time - -We have a working definition of the targets that is in use with CLion and works on modern -CMake (3.15). It breaks on older CMake version (e.g. 3.7) with an error message (issue#7091). -No PoC yet to fix this, but it looks like changing the target properties should do it (in the -worst case we can drop the separate object completely and merge the sources directly into -the final target). - -Steps needed for building a prototype: - -1. Pick a reasonable configuration. -2. Use the PoC techniques above to do a full generation of `CMAKE_` variables in the cache - according to the feature options and dependencies. -3. Push these into the project variables. -4. Work on it until the build succeeds in at least one known configuration. -5. Smoke-test that the output is valid (i.e. the executable loads and runs, and we can - access the dashboard). -6. Do a full comparison of the `config.h` generated by autotools against the CMake version - and document / fix any deviations. - -## CMake install target - -I've only looked at this superficially as we do not have a prototype yet, but each of the -first-stage install steps (in `make install`) and the second-stage (in `netdata-installer.sh`) -look feasible. - -## General issues - -* We need to choose a minimum CMake version that is an available package across all of our - supported environments. There is currently a build issue #7091 that documents a problem - in the compilation phase (we cannot link in libnetdata as an object on old CMake versions - and need to find a different way to express this). - -* The default variable-expansion / comparisons in CMake are awkward, we need this to make it - sane: - ``` - cmake_policy(SET CMP0054 "NEW") - ``` -* Default paths for libs / includes are not comprehensive on most environments, we still need - some heuristics for common locations, e.g. `/usr/local` on FreeBSD. - -# Recommendations - -We should follow these steps: - -1. Build a prototype. -2. Build a test-environment to check the prototype against environments / configurations that - the team uses. -3. Perform an "internal" release - merge the new CMake into master, but not announce it or - offer to support it. -4. Check it works for the team internally. -5. Do a soft-release: offer it externally as a replacement option for autotools. -6. Gather feedback and usage reports on a wider range of configurations. -7. Do a hard-release: switch over the preferred build-system in the installation instructions. -8. Gather feedback and usage reports on a wider range of configurations (again). -9. Deprecate / remove the autotools build-system completely (so that we can support a single - build-system). - -Some smaller miscellaneous suggestions: - -1. Remove the `_Generic` / `strerror_r` config to make the system simpler (use the technique - on the blog post to make the standard version re-entrant so that it is thread-safe). -2. Pull in jemalloc by source into the repo if it is our preferred malloc implementation. - -# Background - -* [Stack overflow starting point](https://stackoverflow.com/questions/7132862/how-do-i-convert-an-autotools-project-to-a-cmake-project#7680240) -* [CMake wiki including previous autotools conversions](https://gitlab.kitware.com/cmake/community/wikis/Home) -* [Commands section in old CMake docs](https://cmake.org/cmake/help/v2.8.8/cmake.html#section_Commands) -* [try_compile in newer CMake docs](https://cmake.org/cmake/help/v3.7/command/try_compile.html) -* [configure_file in newer CMake docs](https://cmake.org/cmake/help/v3.7/command/configure_file.html?highlight=configure_file) -* [header checks in CMake](https://stackoverflow.com/questions/647892/how-to-check-header-files-and-library-functions-in-cmake-like-it-is-done-in-auto) -* [how to write platform checks](https://gitlab.kitware.com/cmake/community/wikis/doc/tutorials/How-To-Write-Platform-Checks) - - |