Lua 5.1 compiled file. Is it possible to modify one or more bytes value to change a equal operation from == to ~=?

Asked Dec 30 '18 at 16:33

Active Dec 30 '18 at 18:16

Viewed 197 times

I have a Lua Compiled file (5.1). I decompiled it and I have this operation:

if L2_3 == "MS" then
  L3_4 = print
  L4_5 = "Mfg install mode"
  L3_4(L4_5)
  L3_4 = true
  return L3_4
else
  L3_4 = print
  L4_5 = "Normal install mode"
  L3_4(L4_5)
end

I need to change bytes oh compiled file, to obtain this:

if L2_3 ~= "MS" then
  L3_4 = print
  L4_5 = "Mfg install mode"
  L3_4(L4_5)
  L3_4 = true
  return L3_4
else
  L3_4 = print
  L4_5 = "Normal install mode"
  L3_4(L4_5)
end

It run on a QNX platform.. I need to change from == to ~= by changing one or more bytes, with a hexadecimal editor, in the compiled lua file... is it possible? thanks

I have witten this on a file and compiled, with == and with ~=, but bytes differences are not applicable on original compiled file...

edited Dec 30 '18 at 18:16

asked Dec 30 '18 at 16:33

Tajadela

Yes, it is possible. But the result file will be bigger in size (as your new strings are longer than old ones). – Egor Skriptunoff Dec 30 '18 at 18:08
Sorry, you are right. I wrote the correct version. Only == to ~= should be the change.. How can I find the byte to modify? thanks – Tajadela Dec 30 '18 at 18:17
Google for a pdf article "A No-Frills Introduction to Lua 5.1 VM Instructions" – Egor Skriptunoff Dec 30 '18 at 22:31
thanks for answer. I have read document, but I'm not a programmer... If I have understood, I have to search 23h to find a EQ operator? If yes, in file, there are no 23h values... – Tajadela Dec 31 '18 at 08:55
Upload your file – Egor Skriptunoff Dec 31 '18 at 11:17
https://drive.google.com/file/d/1a9h4Q73OvTmpTh6BfJfAwRiDs_PzcL1G/view – Tajadela Dec 31 '18 at 11:55
Search for `17,C0,43,03` (at offset `A8`) and replace `17` with `57` – Egor Skriptunoff Dec 31 '18 at 15:08
thanks, it work!. but another question: in similar file, the same change don't work: – Tajadela Dec 31 '18 at 15:49
https://drive.google.com/file/d/1A1RCTEwVYSgoxSDEE7yFjn-Jn4IX-lqF/view?usp=sharing – Tajadela Dec 31 '18 at 15:49
offset `9AB` replace `17` with `57` – Egor Skriptunoff Dec 31 '18 at 16:57
Wonderful! thanks! – Tajadela Dec 31 '18 at 17:23
Hi, another question about same file isochkSingleIso.lua: is it possible to know address where "MS" string is located?? – Tajadela Jan 30 '20 at 09:12
The old link is broken, I don't have a local copy of the file. – Egor Skriptunoff Jan 30 '20 at 10:23
https://drive.google.com/open?id=1NY3ZDM_EX7di1TMtkh0-QGgkyS158LAC – Tajadela Jan 30 '20 at 17:12
in the files I'd like to know the address (absolute or relative) where the MS string is stored. thanks – Tajadela Jan 30 '20 at 17:14
I'm using [this](https://lua-bytecode.github.io/) tool to view bytecode files. File offset is `0x0E60` (isochkSingleIso.lua) and `0x04A9` (isochk.lua). You can replace the string "MS" only with a string of length 2. – Egor Skriptunoff Jan 30 '20 at 19:03

Lua 5.1 compiled file. Is it possible to modify one or more bytes value to change a equal operation from == to ~=?

0 Answers0