使用GCC与静态链接库

Question

我试图使用链接时优化与-flto标志海湾合作委员会（6.1.1）链接时优化。

虽然它与我的代码一起工作正常，但它并未链接到静态链接库我也在构建和链接我的项目（这是Engine和库是glsl-optimizer，仅供参考）。

这里是输出：

... 
/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 
... 

而在此之后，当然，我得到几个“未定义的引用”到一些功能。

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。

而且，我使用CMake的不支持LTO（除英特尔在某些平台上的编译器，所以我读了...）。尽管如此，我试过使用：

set_property(TARGET glsl_optimizer PROPERTY INTERPROCEDURAL_OPTIMIZATION True) 

哪一个没有工作。

而且，我试图GCC的-fuse-linker-plugin标志，没有工作。

我想我得做手工直接使用gcc-ar的老路上，也许还有一些其他的方法？

Answer 1

这里是一个MCVE CMake的项目能重现问题：

$ 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"); 
} 

配置还是不错的：

$ 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 

，生成失败按照问题：

$ 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 

有一个以上一个解决方案一个是将3个注释行 在上述CMakeLists.txt取消注释。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 

此修复程序利用以下事实。

构建破题：

/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的代名词，并gcc-ar是 提供该插件的ar的包装。

的CMake的一个C静态库构建模板是：

CMAKE_C_ARCHIVE_CREATE (= <CMAKE_AR> qc <TARGET> <LINK_FLAGS> <OBJECTS>) 
CMAKE_C_ARCHIVE_FINISH (= <CMAKE_RANLIB> <TARGET>) 

这对于GNU ar等同于：

CMAKE_C_ARCHIVE_CREATE (= <CMAKE_AR> qcs <TARGET> <LINK_FLAGS> <OBJECTS>) 
CMAKE_C_ARCHIVE_FINISH (= true) # Or any other no-op command 

使用这些设置

所以加：

SET(CMAKE_AR "gcc-ar") 

我们很好。

对于C++项目，当然，设置CMAKE_CXX_ARCHIVE_CREATE和CMAKE_CXX_ARCHIVE_FINISH