llvm学习（十）：修复 macOS Catalina 缺失 /usr/include 导致的clang无法使用

Posted on 2019-10-16 Edited on 2021-03-08 In llvm

今天升了macOS10.15，发现自己编译的llvm和clang坏掉了，重新编译也没用，而自带的/usr/clang是没有问题的，发现是 /usr/include 缺失。

==2020年11月19日：big sur 无法修改/usr/include，==

==2020年11月20日：使用cmake初始化时，添加-DDEFAULT_SYSROOT=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk，重新编译，即可解决==

一、背景

Command Line Tools 10.13系列，是拥有/usr/include目录的，之前一直在用。但是在macOS 10.15上无法安装它，就很气。 Command Line Tools 10.14系列，砍掉了32位的编译环境，也砍掉了/usr/include。 macOS 10.15砍掉了 32 位的运行环境，将 / 挂载为 read-only。而自己编译的llvm+clang是不会主动去寻找 MacOSXSDK的头文件的，就出现了找不到头文件的情况。

二、修复过程（中英双语，中文更简单、英文更详细）

人肉diff 一下曾经的

/usr/include

和现在的

/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include

发现后者比前者多出少量的.h 文件，但缺少 c++目录。而现在的 c++目录在

/Library/Developer/CommandLineTools/usr/include/c++

因此思路很简单

1、恢复 c++

1	sudo ln -s /Library/Developer/CommandLineTools/usr/include/c++ /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++

2、重启到 recovery 关掉 SIP

3、重启到操作系统

1 2	sudo mount -uw / sudo ln -s /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include /usr/include

4、重启到 recovery 开启 SIP

5、效果

1 2	➜ lsa /usr/include lrwxr-xr-x 1 root wheel 63B 10 16 14:31 include -> /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include

这时候/usr/include 下面就有 c 和 cpp 常用的头文件了，自己编译的 llvm 和 clang 也就可以正常使用了

三、Repair it

Since Command-Line-Tools >= 10.14, there is no /usr/include path. And after macOS Catalina, ‘/‘ partition is read-only. So I finally fix it by myself. I diff the /usr/include for 10.13 and /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include for 10.15. The only difference is that: - Most of them are the same. - 10.15 has more header files, maybe some new feature. - 10.13 has c++ directory, which is /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++ in macOS 10.15. So do the following things:

add c++ headers

sudo ln -s /Library/Developer/CommandLineTools/usr/include/c++ /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++

reboot to recovery and disable SIP
reboot to desktop,

sudo mount -uw / sudo ln -s /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include /usr/include

reboot to recovery and enable SIP.
result:

➜  lsa /usr/include
lrwxr-xr-x  1 root  wheel    63B 10 16 14:31 include -> /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include

➜  /tmp clang -v test.c
clang version 8.0.0 (tags/RELEASE_800/final)
Target: x86_64-apple-darwin19.0.0
Thread model: posix
........
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Users/leadroyal/pllvm/r/lib/clang/8.0.0/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.

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