如果您使用-v
標誌運行g++
,您會看到它使用的鏈接行。這裏有一個簡單的例子程序:
#include <iostream>
int main(void)
{
std::cout << "Hello, world!" << std::endl;
return 0;
}
而且從運行g++ -v -o example example.cpp
輸出:
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.4-14ubuntu5.1' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5.1)
COLLECT_GCC_OPTIONS='-v' '-o' 'example' '-shared-libgcc' '-mtune=generic'
/usr/lib/gcc/x86_64-linux-gnu/4.4.5/cc1plus -quiet -v -D_GNU_SOURCE example.cpp -D_FORTIFY_SOURCE=2 -quiet -dumpbase example.cpp -mtune=generic -auxbase example -version -fstack-protector -o /tmp/ccV8qjvd.s
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/usr/include/x86_64-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
/usr/include/c++/4.4
/usr/include/c++/4.4/x86_64-linux-gnu
/usr/include/c++/4.4/backward
/usr/local/include
/usr/lib/gcc/x86_64-linux-gnu/4.4.5/include
/usr/lib/gcc/x86_64-linux-gnu/4.4.5/include-fixed
/usr/include
End of search list.
GNU C++ (Ubuntu/Linaro 4.4.4-14ubuntu5.1) version 4.4.5 (x86_64-linux-gnu)
compiled by GNU C version 4.4.5, GMP version 4.3.2, MPFR version 3.0.0-p3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: d92fbc2d715a3b7e0f4133f0c40053e4
COLLECT_GCC_OPTIONS='-v' '-o' 'example' '-shared-libgcc' '-mtune=generic'
as -V -Qy -o /tmp/ccGHR0pc.o /tmp/ccV8qjvd.s
GNU assembler version 2.20.51 (x86_64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.20.51-system.20100908
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../:/lib/:/usr/lib/:/usr/lib/x86_64-linux-gnu/
COLLECT_GCC_OPTIONS='-v' '-o' 'example' '-shared-libgcc' '-mtune=generic'
/usr/lib/gcc/x86_64-linux-gnu/4.4.5/collect2 --build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o example -z relro /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../.. -L/usr/lib/x86_64-linux-gnu /tmp/ccGHR0pc.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crtn.o
哇,什麼亂七八糟的。方便地,鏈接線是最後一個,所以你可以很容易地看到發生了什麼。
正如您在下面的註釋中注意到的,前端使用collect2
而不是ld
。幸運的是,collect2
只是ld
的別名。下面是使用它的一個示例:
首先,讓我們產生一個目標文件:
$ ls
example.cpp
$ c++ -c example.cpp
$ ls
example.cpp example.o
然後,我們將使用前端鏈接它,看看鏈接線:
$ c++ -v -o example example.o
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.4.4-14ubuntu5.1' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.4 --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --disable-werror --with-arch-32=i686 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5.1)
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../:/lib/:/usr/lib/:/usr/lib/x86_64-linux-gnu/
COLLECT_GCC_OPTIONS='-v' '-o' 'example' '-shared-libgcc' '-mtune=generic'
/usr/lib/gcc/x86_64-linux-gnu/4.4.5/collect2 --build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o example -z relro /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib -L/lib/../lib -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../.. -L/usr/lib/x86_64-linux-gnu example.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crtn.o
然後扔掉二進制文件,並鏈接自己(通常,我只是複製/粘貼該行,但爲了便於閱讀,我使用\
s的多行方式):
$ ls
example example.cpp example.o
$ rm example
$ ls
example.cpp example.o
$ ld \
> --build-id \
> --eh-frame-hdr \
> -m elf_x86_64 \
> --hash-style=gnu \
> -dynamic-linker \
> /lib64/ld-linux-x86-64.so.2 \
> -o example \
> -z relro \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crt1.o \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crti.o \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtbegin.o \
> -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 \
> -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 \
> -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib \
> -L/lib/../lib \
> -L/usr/lib/../lib \
> -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../.. \
> -L/usr/lib/x86_64-linux-gnu \
> example.o \
> -lstdc++ \
> -lm \
> -lgcc_s \
> -lgcc \
> -lc \
> -lgcc_s \
> -lgcc \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtend.o \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crtn.o
最後,運行它!
$ ls
example example.cpp example.o
$ ./example
Hello, world!
您可以通過刪除一些參數顯着縮短該鏈接線。下面是最少的一組,我想出了一些試驗後:
$ ld \
> -dynamic-linker \
> /lib64/ld-linux-x86-64.so.2 \
> -o example \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crt1.o \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crti.o \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtbegin.o \
> example.o \
> -L/usr/lib/gcc/x86_64-linux-gnu/4.4.5 \
> -lstdc++ \
> -lc \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/crtend.o \
> /usr/lib/gcc/x86_64-linux-gnu/4.4.5/../../../../lib/crtn.o
這組標誌和庫當然會依靠什麼庫函數和語言功能程序使用。
這樣做是不切實際的。 – rubenvb
@rubenvb是的,我已經說過,我並沒有將它用於實際目的:「我只是這樣做來學習如何去做,而不是爲了實際目的。」你是否倒下了? – gsingh2011
是的,我是downvote。這是一件不好的事情。唯一一次你應該使用ld的時候是你開發自己的操作系統,在這種情況下你可能自己寫了所有的系統庫。這是如此極端的操作系統和系統和配置,它甚至不好笑。 – rubenvb