arm-elf-gdb stepping through the program

1
votes

In my school lab I've been asked to debug a program (written in assembly) step by step using arm-elf-gdb. When I set a break point at _start and then run the program and step through it to display the registers' current values. However, when I try to step, the debugger doesn't show the values of the registers. I used "i r" to display the final values of the registers but I need to see the values changing step by step. Any idea why the debugger isn't displaying the values?

Thanks in advance.

The assembly code:

        .text                          @ Executable code below

_start: .global _start                 @ "_start" is required by the linker
        .global main                   @ "main" is the main program

        b       main                   @ Start the main program

main:                                  @ Entry to function "main"

        mov     r0, #10
        mov     r1, #3
        add     r2, r1, r0             @ r2 = r1 + r0
        sub     r3, r0, r1             @ r3 = r1 - r0
        mul     r1, r0, r1             @ r1 = r0 * r1
        swi     0x11                   @ Software interrupt to terminate

        .end
2
assemblygdbarm

2 Answers

2
votes

You could create a gdb macro to show the registers after every step:

(gdb) def z
Type commands for definition of "z".
End with a line saying just "end".
>si
>i r
>end
(gdb) z
r0             0x1  1
r1             0x69b6cae8   1773587176
r2             0x0  0
r3             0x69b6502c   1773555756
r4             0x620f14c0   1645155520
r5             0x68613870   1751201904
r6             0x0  0
r7             0x632aa214   1663738388
r8             0x699c5c50   1771854928
r9             0x632aa20c   1663738380
1
votes

You could use gdb's display command. But you do need to add all registers manually.

display $r0
display $r1
...

You can save some typing by using gdb startup script (-x parameter).