Hook trampoline does not pad remaining bytes with NOPs after JMP patch

[the1234321]

When hooking a function with libmem, the generated JMP patch does not fill the remaining overwritten bytes with NOP instructions.

Original code:

test.exe+28D5BF - 8B 04 85 54 42 A9 00  - mov eax,[eax*4+test.exe+694254]
test.exe+28D5C6 - C3                    - ret
test.exe+28D5C7 - 90                    - nop
test.exe+28D5C8 - 53                    - push ebx
test.exe+28D5C9 - 83 EC 1C              - sub esp,1C

After hooking test.exe+28D5BF, libmem correctly writes the JMP instruction, but the remaining bytes are left untouched:

test.exe+28D5BF - E9 3C2A5104           - jmp 04BA0000
test.exe+28D5C4 - A9 00C39053           - test eax,5390C300
test.exe+28D5C9 - 83 EC 1C              - sub esp,1C

This causes the disassembly to become corrupted because the original instruction length was 7 bytes, while the JMP instruction only uses 5 bytes.

Expected behavior:

test.exe+28D5BF - E9 3C2A1C0C           - jmp 0C850000
test.exe+28D5C4 - 90                    - nop
test.exe+28D5C5 - 90                    - nop
test.exe+28D5C6 - C3                    - ret
test.exe+28D5C7 - 90                    - nop
test.exe+28D5C8 - 53                    - push ebx
test.exe+28D5C9 - 83 EC 1C              - sub esp,1C

It would be helpful if libmem could automatically pad the remaining bytes with NOPs when the overwritten instruction size is larger than the JMP patch size.