adding more space to linear executable dos games

[dion]

Hi,
i am working on an old LE exe dos game, and would like to change some opcodes. the problem is, i need more space on the code segment to make my changes. i have search the internet for tools, but i don't find any. Does anyone know something like that?

[Rufflito]

Originally Posted by dion

Hi,
i am working on an old LE exe dos game, and would like to change some opcodes. the problem is, i need more space on the code segment to make my changes. i have search the internet for tools, but i don't find any. Does anyone know something like that?

Creating code caves is trivial for PEs but if it's for a native DOS app I need to see the executable first (some very old ones impose the 640 kb limit for RAM). Consider posting it?
Or for a start you can do a google search for "code caves" if you didn't already do so.

[dion]

Yes, i have search for code cave, but nothing for LE file.
The game was compiled with watcom c++ with dos4gw stub. It was mix of 16 and 32 bit program. The program itself is 32 bit, the loader is 16 bit.

For a reason, i would not post the file here, but there seems to be many dos4gw games out there. There is a github that make program to edit LE, but it is not implemented yet. I also see a wiki that have tutorial's title the same with this thread, but it was empty, unfortunately.

[chants]

Is there padding between functions? Often single byte padding of 0s, int3s, nops will pad functions to align them, not sure in the old LE exes if this was common. The only key is to jump there and back making sure to not interfere with any code containing relocated addresses.

[NON]

Originally Posted by chants

Is there padding between functions? Often single byte padding of 0s, int3s, nops will pad functions to align them, not sure in the old LE exes if this was common. The only key is to jump there and back making sure to not interfere with any code containing relocated addresses.

It's much better to add another new section. Then no major limits to the bytes you can add.

[sendersu]

Originally Posted by dion

Hi,
i am working on an old LE exe dos game, and would like to change some opcodes. the problem is, i need more space on the code segment to make my changes. i have search the internet for tools, but i don't find any. Does anyone know something like that?

I"m wondering how did you manage to debug this kind of ancient stuff?
what kind of tools are you using

[dion]

Originally Posted by sendersu

I"m wondering how did you manage to debug this kind of ancient stuff?
what kind of tools are you using

Using dosbox debugger.

[OldieHans]

Originally Posted by sendersu

I"m wondering how did you manage to debug this kind of ancient stuff?
what kind of tools are you using

That is not the most important question here...
The most shocking question that is staring at me is, how someone (user @dion) with just 2... That is right... Someone with just TWO freaking reps can gain the VIP status in this forum while many a genuine users need to wait for a day to get their posts 'approved' by the admins...

What a huge disparity...

[dion]

for anyone need, i put my own tool here here