$ cat /etc/apt/sources.list
deb https://mirrors.ustc.edu.cn/debian testing main non-free contrib
deb https://http.debian.net/debian jessie-backports main

$ apt-get install gcc-arm-none-eabi gdb-arm-none-eabi cmake openocd

$ mkdir build
$ cd build
$ cmake ../hello
$ make

$ openocd -f ../openocd.cfg

$ telnet localhost 4444
> halt
target state: halted
target halted due to debug-request, current mode: Thread
xPSR: 0x01000000 pc: 0x080001f8 msp: 0x20001fe8
> flash write_image main.bin 0x08000000
wrote 1200 bytes from file main.bin in 0.064027s (18.303 KiB/s)
>

$ arm-none-eabi-gdb main.elf
(gdb) target remote localhost:3333
Remote debugging using localhost:3333
0x080001da in inc () at /home/tom/Desktop/stm32/demo/hello/main.c:6
6     i+=off;
(gdb) monitor reset halt
...
(gdb) load
Loading section .text, size 0x498 lma 0x8000000
Loading section .data, size 0x18 lma 0x8000498
Start address 0x8000214, load size 1200
Transfer rate: 2 KB/sec, 600 bytes/write.

(gdb) p i
$1 = 0
(gdb) p off
$2 = 5

(gdb) continue
...