Debug.mac cannot handle argument involving rsp correctly

Programming x86-64 Assembly
1

Reproducible code snippet:

    push 2
    debugx64 [rsp]
    mov rax, rsp
    debugx64 [rax]
    pop rax
    debugx64 rax

Expected result: print 2 three times.

Actual result:

debug hexadecimal... 75BF700F1CB0
debug hexadecimal... 2
debug hexadecimal... 2

(Note that 75BF700F1CB0 part is always changing)

It might because of debug routine using stack to preserve other registers.

If it is implementation limitation, I recommended to document involving rsp causes unexpected result.

1 Like
2

Yes, this is documented in the document on the section CALLING CONVENTION

; Note that the stack is modified temporarily by all macros.
; This means any value pointed by RSP won't be valid at the time it is dereferenced.
; Such value should be loaded on a register before debugging.

Do you think this message could be more evident? Perhaps I could reinforce it on the other sections.

3

Then, this is my fault not looking debug.mac thoughtfully.

For excuse, it would be good to mention this on “How to debug” part on instruction of each exercise.

1 Like
4

You’re right, I’ll add this information. Thank you!

5

This PR added a note on “How to debug”.