我正在尝试使用GCC(6.1.1)的-flto
标志进行链接时优化。
虽然它与我的代码工作正常,但它没有链接到静态链接库我也正在建立和链接我的项目(这是Engine和库是glsl-optimizer,仅供参考)。
这是输出:
...
/usr/bin/ranlib: ir_expression_flattening.cpp.o: plugin needed to handle lto object
/usr/bin/ranlib: opt_function_inlining.cpp.o: plugin needed to handle lto object
/usr/bin/ranlib: opt_copy_propagation_elements.cpp.o: plugin needed to handle lto object
...
在那之后,当然,我得到一些函数的几个“未定义的引用”。
我做了一些研究,发现它可能是因为ar
,我应该尝试使用gcc-ar
,但我不知道我该怎么做。
另外,我正在使用不支持lto的CMake(在某些平台上除英特尔编译器外,所以我读了......)。尽管如此,我尝试使用:
set_property(TARGET glsl_optimizer PROPERTY INTERPROCEDURAL_OPTIMIZATION True)
哪个没用。
此外,我尝试了GCC的-fuse-linker-plugin
旗帜,但没有奏效。
我想我将不得不直接使用gcc-ar
手动执行旧方法,或者可能还有其他一些方法?
这是一个重现问题的MCVE CMake项目:
$ ls -R hellow
hellow:
CMakeLists.txt hello.c libhello.c
$ cat hellow/CMakeLists.txt
cmake_minimum_required (VERSION 2.6)
project (hellow)
SET(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -flto")
SET(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -flto")
#SET(CMAKE_AR "gcc-ar")
#SET(CMAKE_C_ARCHIVE_CREATE "<CMAKE_AR> qcs <TARGET> <LINK_FLAGS> <OBJECTS>")
#SET(CMAKE_C_ARCHIVE_FINISH true)
add_library(hello STATIC libhello.c)
add_executable(hellow hello.c)
target_link_libraries(hellow hello)
add_dependencies(hellow hello)
$ cat hellow/hello.c
extern void hello(void);
int main(void)
{
hello();
return 0;
}
$ cat hellow/libhello.c
#include <stdio.h>
void hello(void)
{
puts("Hello");
}
配置很好:
$ mkdir build_hellow
$ cd build_hellow/
$ cmake ../hellow
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/imk/dev/so/build_hellow
根据问题构建失败:
$ make
Scanning dependencies of target hello
[ 25%] Building C object CMakeFiles/hello.dir/libhello.c.o
[ 50%] Linking C static library libhello.a
/usr/bin/ar: CMakeFiles/hello.dir/libhello.c.o: plugin needed to handle lto object
/usr/bin/ranlib: libhello.c.o: plugin needed to handle lto object
[ 50%] Built target hello
Scanning dependencies of target hellow
[ 75%] Building C object CMakeFiles/hellow.dir/hello.c.o
[100%] Linking C executable hellow
/tmp/ccV0lG36.ltrans0.ltrans.o: In function `main':
<artificial>:(.text+0x5): undefined reference to `hello'
collect2: error: ld returned 1 exit status
CMakeFiles/hellow.dir/build.make:95: recipe for target 'hellow' failed
make[2]: *** [hellow] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/hellow.dir/all' failed
make[1]: *** [CMakeFiles/hellow.dir/all] Error 2
Makefile:83: recipe for target 'all' failed
make: *** [all] Error 2
有多个解决方案。一个是在上面的CMakeLists.txt
中取消注释3个注释行。然后:
$ cmake ../hellow/
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/imk/dev/so/build_hellow
$ make
Scanning dependencies of target hello
[ 25%] Building C object CMakeFiles/hello.dir/libhello.c.o
[ 50%] Linking C static library libhello.a
[ 50%] Built target hello
Scanning dependencies of target hellow
[ 75%] Building C object CMakeFiles/hellow.dir/hello.c.o
[100%] Linking C executable hellow
[100%] Built target hellow
$ ./hellow
Hello
此修复程序使用以下事实。
破坏性问题:
/usr/bin/ar: CMakeFiles/hello.dir/libhello.c.o: plugin needed to handle lto object
...
/usr/bin/ranlib: libhello.c.o: plugin needed to handle lto object
可以通过给ar
和ranlib
选项解决:
--plugin=$(gcc --print-file-name=liblto_plugin.so)
然而,GNU ranlib
仅仅是ar -s
的同义词,而gcc-ar
是ar
的包装,提供该插件。
CMake的C静态库的构建模板是:
CMAKE_C_ARCHIVE_CREATE ( = <CMAKE_AR> qc <TARGET> <LINK_FLAGS> <OBJECTS>)
CMAKE_C_ARCHIVE_FINISH ( = <CMAKE_RANLIB> <TARGET>)
对于GNU ar
来说相当于:
CMAKE_C_ARCHIVE_CREATE ( = <CMAKE_AR> qcs <TARGET> <LINK_FLAGS> <OBJECTS>)
CMAKE_C_ARCHIVE_FINISH ( = true) # Or any other no-op command
所以使用这些设置加:
SET(CMAKE_AR "gcc-ar")
我们很好。
当然,对于C ++项目,设置CMAKE_CXX_ARCHIVE_CREATE
和CMAKE_CXX_ARCHIVE_FINISH