lang似乎使用gcc [英] clang appears to use gcc
问题描述
当我使用clang编译一个简单的hello world程序时，在elf64文件的注释中，我仍然找到与GCC相关的信息。为什么？我正在使用clang而不是gcc。
When I compile a simple hello world program using clang, in the comments of the elf64 file I still find information related to GCC. Why? I'm using clang not gcc.
我正在使用ubuntu 16.04。
I'm using ubuntu 16.04.
username@ubuntu:~$ clang++ -stdlib=libc++ test.cpp
username@ubuntu:~$ objdump --full-contents --section=.comment a.out
a.out: file format elf64-x86-64
Contents of section .comment:
0000 4743433a 20285562 756e7475 20352e34 GCC: (Ubuntu 5.4
0010 2e302d36 7562756e 7475317e 31362e30 .0-6ubuntu1~16.0
0020 342e3429 20352e34 2e302032 30313630 4.4) 5.4.0 20160
0030 36303900 636c616e 67207665 7273696f 609.clang versio
0040 6e20342e 302e3020 28746167 732f5245 n 4.0.0 (tags/RE
0050 4c454153 455f3430 302f6669 6e616c29 LEASE_400/final)
0060 00 .
username@ubuntu:~$
test.cpp是：
test.cpp is:
#include <iostream>
int main(int argc, char* argv[])
{
std::cout << argc << std::endl;
return 0;
}
我也参加了
username@ubuntu:~$ sudo update-alternatives --config c++
[sudo] password for username:
There are 2 choices for the alternative c++ (providing /usr/bin/c++).
Selection Path Priority Status
------------------------------------------------------------
0 /usr/bin/g++ 20 auto mode
* 1 /usr/bin/clang++-libc++ 5 manual mode
2 /usr/bin/g++ 20 manual mode
Press <enter> to keep the current choice[*], or type selection number:
username@ubuntu:~$
可以吗？为什么？
推荐答案
这是因为您正在与使用GCC构建的C运行时（来自Glibc）进行链接，并且链接器正在合并
It's because you're linking with a C runtime (from Glibc) built with GCC, and the linker is merging the two together.
$ clang++ -c --stdlib=libc++ test.cpp
$ objdump --full-contents --section=.comment test.o
test.o: file format elf64-x86-64
Contents of section .comment:
0000 00636c61 6e672076 65727369 6f6e2034 .clang version 4
0010 2e302e30 20287461 67732f52 454c4541 .0.0 (tags/RELEA
0020 53455f34 30302f66 696e616c 2900 SE_400/final).
$ clang++ --verbose test.o
"/usr/bin/ld" --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crt1.o /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crti.o /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/crtbegin.o -L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1 -L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64 -L/usr/bin/../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../.. -L/usr/bin/../lib -L/lib -L/usr/lib test.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/crtend.o /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crtn.o
$ objdump --full-contents --section=.comment /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crt1.o
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/6.3.1/../../../../lib64/crt1.o: file format elf64-x86-64
Contents of section .comment:
0000 00474343 3a202847 4e552920 362e332e .GCC: (GNU) 6.3.
0010 31203230 31373033 303600 1 20170306.
$ objdump --full-contents --section=.comment a.out
a.out: file format elf64-x86-64
Contents of section .comment:
0000 4743433a 2028474e 55292036 2e332e31 GCC: (GNU) 6.3.1
0010 20323031 37303330 3600636c 616e6720 20170306.clang
0020 76657273 696f6e20 342e302e 30202874 version 4.0.0 (t
0030 6167732f 52454c45 4153455f 3430302f ags/RELEASE_400/
0040 66696e61 6c2900 final).
我的系统的版本与您的系统略有不同，但是您可以看到Clang编译的对象仅具有其中的Clang标识符，C运行时对象中具有GCC标识符，而最终的二进制文件中都包含GCC标识符。
My system has slightly different versions from yours, but you can see that the Clang-compiled object only has the Clang identifier in it, the C runtime object has the GCC identifier in it, and the final binary has both.
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