Open Terminal:
sudo apt install gdb-multiarch
if gdb - uses i386 registers:
sudo apt remove gdb gdbserver
sudo apt install gdb-arm-none-eabi
qemu-system-arm -M sx1 -S -kernel a.out -s -nographic -serial pty
-M sx1 http://wiki.qemu.org/Documentation/Platforms/ARM
-S freeze CPU at startup (use 'c' to start execution)
-s shorthand for -gdb tcp::1234
-nographic disable graphical output and redirect serial I/Os to console
-monitor stdio redirect the monitor to stdio
Inspect Registers:
info registers
Run qemu-system-arm in a seprate window:
Run GDB:
gdb-multiarch
or
arm-none-eabi-gdb
Connect to running code:
target remote localhost:1234
Set PC to beginning of ADD.s
set $pc = 0x10010034
Inspect Registers
info registers
View RAM
x/4i $pc
x/4i $pc
Examine 4 Instructions from current PC + 12 (Bytes) i.e. 3 instructions
PC ends on 0x10010040 Therefore program begins on 0x10010034
0x10010040 - 12 (3 lines x 4 bytes) = 0x10010034
x/4i $pc - 12 to see RAM at the end.
View instructions in HEX:
x/4w $pc
Step through code:
stepi
Print Register:
p $r0
Print Register 0
R15 in ARM is the PC
add.s example PC ends on 0x10010040
Each instruction is 32 bits wide or 4 Bytes
There are 3 instructions of width 4 (bytes)
If -S then PC is 0x10000000
By default the registers are little-endian (smallest on the right)
R0-R12 are general purpose
R13, R14, R15 & PSR are special purpose
R13: Stack Pointer, R14: Link Register, R15: Program Counter
PSR: Program Status Register
4 left most bits of the PSR register are status flags NZCV
- Negative
- Zero
- Carry
- oVerflow
Ref:
https://www.ece.cmu.edu/~ee349/f-2012/lab2/qemu.pdf
http://users.ece.utexas.edu/~valvano/EE345M/Arm_EE382N_4.pdf