ARM assembly debugging

I've been learning ARM assembly recently, but ARM is not as easy to debug as x86. Fortunately, there are virtual machines and universal debuggers like GDB. After searching Google for a long time and combining my own practice, I finally succeeded in debugging ARM assembly. I would like to share this with students who are interested in ARM embedded systems.

First, let me explain the tools you need
. 1. QEMU This emulator can not only simulate x86, but also ARM and MIPS, which is very powerful.
2. GDB (source code) Needless to say, it is a universal debugger, but it needs to be compiled from source code.
3. arm-linux cross toolchain I use the 3.4 version that comes with my own development board, but you can just download one from www.uclinux.org

(but it seems that uclinux has been blocked by GFW...) Compile GDB first and set the target to the ARM platform:
$ ./configure --target=arm-linux
$ make

$ make install

Note: The default directory is /usr/local/bin/

OK, start writing the assembly program. The sample code is very simple. It assigns values ​​to three registers and then loops endlessly. Note that there must be an endless loop, otherwise illegal instructions or unknown instructions will be encountered.

=======test.S========
.globl _start
_start:
  mov r0, #0
  mov r1, #1
  mov r2, #2
loop:
  b loop
=======EOF=========

Compile:
$ arm-linx-as -o test.o test.SLink
:
$ arm-linux-ld -o test test.oNow
you can use objdump to view the contents of test:
$ arm-linux-objdump -d testThe
next step is debugging. Use qemu to start gdb port monitoring:
$ qemu-arm -g 11111 testAfter
starting gdb, note that test must be specified when starting. You cannot use file to specify test after starting (why not, it's not clear, but it's the test result):
$ arm-linux-gdb /PATH_TO_TEST Note that the gdb here is not the system's gdb, but the gdb just compiled
(gdb) target remote localhost:11111 Set the target to the local port 11111
(gdb) disassemble Disassembly
(gdb) display /10i $pc-16 This command displays the 10 instructions near the current pc, replacing the list command for debugging x86 programs
(gdb) si si, not s, is a single-step execution instruction. If it is s, it will execute to the next label. Similar to ni
(gdb) info register Well, this is to view the value of the register~
(gdb) x /16 0 This is to view the memory information of the 16 words (32 bits per word) starting from 0x00000000

That's about it. There is a problem that I don't know how to set the breakpoint of the instruction. I'll try it later...
If you run the program directly, directly

qemu-arm test
Now you can practice while reading the book~ QEMU also supports Thumb instruction set and Jazelle instruction set, which should be debugged in this way