gdb doesn't work on macos High Sierra 10.13.3

I have installed gdb 8.1 with brew.

I have codesign gdb also and .gdbinit as below:

set startup-with-shell off.

I have disabled SIP feature:

$ csrutil status
System Integrity Protection status: disabled.

But gdb still doesn't work:

#include <iostream>
using namespace std;

int main() {
  cout << "hello world!" << endl;
  return 0;
}

Compile command:

g++ -g test.cpp

gdb output:

GNU gdb (GDB) 8.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-apple-darwin17.3.0".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from a.out...Reading symbols from /Users/mypc/Downloads/a.out.dSYM/Contents/Resources/DWARF/a.out...done.
done.
(gdb) run
Starting program: /Users/mypc/Downloads/a.out 
[New Thread 0x2503 of process 802]
[New Thread 0x2303 of process 802]
During startup program terminated with signal ?, Unknown signal.
(gdb) 

What correct steps to make gdb work on macos sierra?

This is caused by latest gdb 8.1, downgrade gdb to 8.0.1 could solve this problem.

How to downgrade to gdb 8.0.1

• Unlink current gdb: brew unlink gdb
• Install gdb 8.0.1: brew install https://raw.githubusercontent.com/Homebrew/homebrew-core/9ec9fb27a33698fc7636afce5c1c16787e9ce3f3/Formula/gdb.rb
• Optional: avoid upgrade gdb with brew pin gdb

in my case downgrading to 8.0.1 didn't help.
but the following steps helped.

(i inserted step 12, "check if it works" because, instead of restarting i've tested gdb and it worked just fine. i didn't follow the steps 12+)

1. Open Keychain Access
2. In menu, open Keychain Access > Certificate Assistant > Create a certificate
3. Give it a name (e.g. gdb-cert)
   • Identity type: Self Signed Root
   • Certificate type: Code Signing
   • Check: let me override defaults
4. Continue until "specify a location for..."
5. Set Keychain location to System
6. Create certificate and close Certificate Assistant.
7. Find certificate in System keychain.
8. Double click the certificate
9. Expand Trust, set Code signing to always trust
10. Restart taskgated in terminal: killall taskgated
11. Codesign gdb using your certificate: codesign -fs gdb-cert /usr/local/bin/gdb
12. --- CHECK IF IT WORKS ---
13. Shut down your mac and restart in recovery mode (hold down command-Runtil apple logo appears)
14. Open terminal window
15. Modify System Integrity Protection to allow debugging: csrutil enable --without debug
16. Reboot your Mac
17. Debugging with gdb should now work as expected.

information source:
pre Sierra: https://gist.github.com/hlissner/898b7dfc0a3b63824a70e15cd0180154
Sierra: https://gist.github.com/gravitylow/fb595186ce6068537a6e9da6d8b5b96d