macOS gdb: please check gdb is codesigned

# 问题描述：Mac OS Sierra 无法使用gdb调试

• Unable to find Mach task port for process-id 47072: (os/kern) failure (0x5).
• (please check gdb is codesigned - see taskgated(8))
• During startup program terminated with signal SIG113, Real-time event 113.

# 如果是用Homebrew安装的gdb，brew install gdb，安装完有提示

gdb requires special privileges to access Mach ports.
You will need to codesign the binary. For instructions, see:
https://sourceware.org/gdb/wiki/BuildingOnDarwin

On 10.12 (Sierra) or later with SIP, you need to run this:
echo “set startup-with-shell off” >> ~/.gdbinit

在macOS上，gdb使用Mach ports需要特殊权限
你需要对二进制文件进行签名。指导步骤，查看：
https://sourceware.org/gdb/wiki/BuildingOnDarwin

在10.12 (Sierra) 或之后带SIP的操作系统版本，你还需要运行这个命令：
echo “set startup-with-shell off” >> ~/.gdbinit

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# 解决方法

# 具体操作，按照https://sourceware.org/gdb/wiki/BuildingOnDarwin步骤2开始
# 2. Giving gdb permission to control other processes

1. 启动 /Applications/Utilities/Keychain Access.app
2. 顶部菜单选择 /Keychain Access/Certificate Assistant/Create a Certificate…
3. Create Your Certificate
   
   • Name: gdb-cert
   • Identity Type: Self Signed Root
   • Certificate Type: Code Signing
   • 勾选 Let me override defaults
4. 一直按continue，直到Specify a Location For The Certificate
   
   • Keychain: System
   • tips: 如果无法将Certificate保存到System keychain，就先保存到login keychain，然后导出，再导入到System keychain。
5. Create
6. 如附图，右键选择gdb-cert的Get Info，打开Trust项，将Code Signing改成Always Trust
7. 最后退出Keychain Access以刷新存储证书
8. codesign gdb，执行
   
   • codesign -s gdb-cert $(which gdb)
9. macOS 10.12 (Sierra) 或以上版本的操作系统
   
   • 需要使用 gdb 7.12.1 之上的版本
   • 此外，为防止gdb利用shell来启动程序开始debug，执行下面的语句
     echo "set startup-with-shell off" >> ~/.gdbinit
10. 重启系统

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