1From fa5ec96a94646492a3f908e12905b3e48a8e800b Mon Sep 17 00:00:00 2001 2From: Romain Naour <romain.naour@gmail.com> 3Date: Wed, 18 Apr 2018 20:24:13 +0200 4Subject: [PATCH] src/cpp: fix cmake >= 3.11 build 5 6CMake < 3.11 doesn't support add_library() without any source file 7(i.e add_library(foo SHARED)). But flann CMake use a trick that use 8an empty string "" as source list (i.e add_library(foo SHARED "")). 9This look like a bug in CMake < 3.11. 10 11With CMake >= 3.11, the new behaviour of add_library() break the 12existing flann CMake code. 13 14From CMake Changelog [1]: 15"add_library() and add_executable() commands can now be called without 16 any sources and will not complain as long as sources are added later 17 via the target_sources() command." 18 19Note: flann CMake code doesn't use target_sources() since no source file 20are provided intentionally since the flann shared library is created by 21linking with the flann_cpp_s static library with this line: 22 23target_link_libraries(flann_cpp -Wl,-whole-archive flann_cpp_s -Wl,-no-whole-archive) 24 25If you try to use "add_library(flann_cpp SHARED ${CPP_SOURCES})" (as it should 26be normally done), the link fail due to already defined symbol. 27 28They are building the shared version using the static library "to speedup the 29build time" [3] 30 31This issue is already reported upstream [2] with a proposed solution. 32 33Upstream status: Pending 34 35Fixes: 36http://autobuild.buildroot.net/results/b2f/b2febfaf8c44ce477b3e4a5b9b976fd25e8d7454 37 38[1] https://cmake.org/cmake/help/v3.11/release/3.11.html 39[2] https://github.com/mariusmuja/flann/issues/369 40[3] https://github.com/mariusmuja/flann/commit/0fd62b43be2fbb0b8d791ee36290791224dc030c 41 42Signed-off-by: Romain Naour <romain.naour@gmail.com> 43--- 44 src/cpp/CMakeLists.txt | 4 ++-- 45 src/cpp/empty.cpp | 1 + 46 2 files changed, 3 insertions(+), 2 deletions(-) 47 create mode 100644 src/cpp/empty.cpp 48 49diff --git a/src/cpp/CMakeLists.txt b/src/cpp/CMakeLists.txt 50index b44a735..a816863 100644 51--- a/src/cpp/CMakeLists.txt 52+++ b/src/cpp/CMakeLists.txt 53@@ -29,7 +29,7 @@ if (BUILD_CUDA_LIB) 54 endif() 55 56 if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND CMAKE_COMPILER_IS_GNUCC) 57- add_library(flann_cpp SHARED "") 58+ add_library(flann_cpp SHARED "empty.cpp") 59 set_target_properties(flann_cpp PROPERTIES LINKER_LANGUAGE CXX) 60 target_link_libraries(flann_cpp -Wl,-whole-archive flann_cpp_s -Wl,-no-whole-archive) 61 62@@ -85,7 +85,7 @@ if (BUILD_C_BINDINGS) 63 set_property(TARGET flann_s PROPERTY COMPILE_DEFINITIONS FLANN_STATIC) 64 65 if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND CMAKE_COMPILER_IS_GNUCC) 66- add_library(flann SHARED "") 67+ add_library(flann SHARED "empty.cpp") 68 set_target_properties(flann PROPERTIES LINKER_LANGUAGE CXX) 69 target_link_libraries(flann -Wl,-whole-archive flann_s -Wl,-no-whole-archive) 70 else() 71diff --git a/src/cpp/empty.cpp b/src/cpp/empty.cpp 72new file mode 100644 73index 0000000..40a8c17 74--- /dev/null 75+++ b/src/cpp/empty.cpp 76@@ -0,0 +1 @@ 77+/* empty */ 78-- 792.14.3 80 81