Fix asm() instruction consistency

[rtlcopymemory]

Fix asm() instruction consistency

Expected Behaviour

When using either asm() with the vma parameter or the ELF.asm() function with an instruction like nop I expect it to write 1 byte 0x90 at the specified position.

Actual behaviour

Depending on the memory address specified (either as vma or as first parameter of ELF.asm()) it will add padding nop bytes before the instruction. More specifically, if the address is not a multiple of 4 (address % 4 != 0) it will add 4 - (address % 4) padding bytes making it sometimes hard to patch instructions smaller than 4 bytes.

Example Script

Running this script will quickly demonstrate the effect

from pwn import *

for i in range(17):
    print(f"{i}", asm("INT 3", vma=i))

Output before changes

0 b'\xcc'
1 b'f\x90\x90\xcc'
2 b'f\x90\xcc'
3 b'\x90\xcc'
4 b'\xcc'
5 b'f\x90\x90\xcc'
6 b'f\x90\xcc'
7 b'\x90\xcc'
8 b'\xcc'
9 b'f\x90\x90\xcc'
10 b'f\x90\xcc'
11 b'\x90\xcc'
12 b'\xcc'
13 b'f\x90\x90\xcc'
14 b'f\x90\xcc'
15 b'\x90\xcc'
16 b'\xcc'

Output after changes

0 b'\xcc'
1 b'\xcc'
2 b'\xcc'
3 b'\xcc'
4 b'\xcc'
5 b'\xcc'
6 b'\xcc'
7 b'\xcc'
8 b'\xcc'
9 b'\xcc'
10 b'\xcc'
11 b'\xcc'
12 b'\xcc'
13 b'\xcc'
14 b'\xcc'
15 b'\xcc'
16 b'\xcc'

Testing

I was not able to start the whole test suite but I tried testing at least the asm part which doesn't start on only one architecture (it isn't failing, I'm missing some dependency).
The Docker image also seems to fail to build at the apt update step.
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

This, therefore, might require at least someone who can run all the tests to test them again

(First time contributing to a project, I hope I did this right, I apologize if I made a mistake either choosing the wrong target branch or in the rest of the pull request)

[Arusekk]

TIL: apparently thumb also needs .p2align 2, the CI is failing now. :-)