33

我正在尝试使用带有-fltoGCC (6.1.1) 标志的链接时优化。

虽然它适用于我的代码，但它没有链接到我也在构建和链接我的项目的静态链接库（它是Engine并且库是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，我得到了一些对某些函数的“未定义引用”。

我做了一些研究，发现这可能是因为ar，我应该尝试使用gcc-ar，但我不确定我该怎么做。

另外，我正在使用不支持 lto 的 CMake（某些平台上的英特尔编译器除外，所以我读了......）。即使，我尝试使用：

set_property(TARGET glsl_optimizer PROPERTY INTERPROCEDURAL_OPTIMIZATION True)

这没有用。

另外，我尝试了 GCC 的-fuse-linker-plugin标志，但它不起作用。

我想我必须直接使用旧方法手动完成gcc-ar，或者可能有其他方法？

4

2 回答 2

30

这是一个重现该问题的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");
}

配置不错：

$ 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

解决方案不止一种。一种是取消注释CMakeLists.txt上面的 3 行注释。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

此修复程序利用了以下事实。

构建破坏问题：

/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

可以通过给出ar和ranlib选项来解决：

--plugin=$(gcc --print-file-name=liblto_plugin.so)

但是，GNUranlib只是 的同义词ar -s，并且是提供该插件gcc-ar的包装器。ar

CMake 的 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 GNUar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

因此，通过这些设置加上：

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

于 2016-08-31T17:49:24.733 回答
0

移植到 g++-11 后我遇到了类似的问题。这可能是由于默认值的更改 - 使用“slim”对象而不是“fat” - 并添加-ffat-lto-objects解决了它。

另请参阅此 SO 答案和那里的评论。

于 2021-09-01T17:19:32.163 回答