Metal Gear annotated disassembly published

by konamiman on 05-10-2018, 21:34
Topic: Software
Languages:

Manuel Pazos has been spending a good amount of time reverse-engineering the classic MSX game Metal Gear and publishing some interesting findings about it in his twitter account. The process has finished and Manuel has just published the result of his work as a GitHub respository containing a fully annotated disassembly of the game, for both the Japanese and the English versions. So now we have the opportunity to take a look at the ins and outs of this masterpiece and learn a bit about how Konami developed their masterpieces.

Relevant link: Metal Gear annotated disassembly at GitHub

Comments (38)

By Dustin Pease

Resident (50)

Dustin Pease's picture

06-10-2018, 00:05

Manuel,
You are awesome. Thank you so much for this!

By Victor

Champion (402)

Victor's picture

06-10-2018, 05:27

What a titanic work...

Thanks for sharing, Manuel!!

By Pippo

Champion (419)

Pippo's picture

06-10-2018, 07:31

Astonishing work!!! Shocked! Shocked!
You spent very happy hours, didn't you, Master Manuel? Smile2

By cax

Prophet (3721)

cax's picture

06-10-2018, 07:56

Very impressive. Can you share the insights now - e.g. how many different code styles can you spot, hidden features etc. ?

By Pippo

Champion (419)

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06-10-2018, 08:07

Many, many thanks, Master Manuel, for your deep dedication to the Sacred System. Smile Smile

By Guillian

Prophet (3164)

Guillian's picture

06-10-2018, 09:00

Thanks guys!

@cax: there are at least two different coding styles. In this Twitter thread I posted some oddities (most of them in Spanish). There are a few more commented in the code.

By KdL

Paragon (1122)

KdL's picture

06-10-2018, 11:35

Congrats Manuel !! Smile

By Pencioner

Hero (654)

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06-10-2018, 12:09

Great stuff! Can't imagine how much of efforts has been put on this Big smile

By ren

Paragon (1154)

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06-10-2018, 13:38

Wow.. So I guess we might expect some fan game(s) / 'remixes' based on these sources..? Cool

Would there be other works you're interested in to disassemble? Gradius 2 or Usas perhaps? Hannibal

By Guillian

Prophet (3164)

Guillian's picture

06-10-2018, 15:14

Thanks!

@ren: I could do the same with other games, but... not really sure if it is worth the effort.

By sd_snatcher

Prophet (2837)

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06-10-2018, 15:49

Impressive, Snake! I mean, Manuel! Smile

By Wolverine_nl

Paladin (938)

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06-10-2018, 16:05

Great job Manuel! Big smile
It is nice to see in the 80's Konami kitchen this way. Your effort was definitly worth it.

By gdx

Prophet (2268)

gdx's picture

06-10-2018, 16:11

Thanks for sharing this impressive work.
Which disassembler did you use?

By lintweaker

Expert (77)

lintweaker's picture

06-10-2018, 16:12

Wow, great job!

By Giangiacomo Zaffini 2

Expert (73)

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06-10-2018, 19:53

Thank Manuel for his gigantic effort.
I cannot even imagine how to revert machine code blob into source assembly modules, functions and variables.
Are You an university resercher or university instructor or professor?

By Guillian

Prophet (3164)

Guillian's picture

06-10-2018, 21:59

Thanks!

@gdx: I used IDA

@Giangiacomo: I'm not related to univertity or teaching. I'm just a MSX fan (^_^)

By Meits

Scribe (5108)

Meits's picture

06-10-2018, 22:54

But... Are there things you can NOT do as well?

By konamiman

Paladin (949)

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07-10-2018, 12:15

Meits wrote:

But... Are there things you can NOT do as well?

He almost can't write README files. Big smile

By Guillian

Prophet (3164)

Guillian's picture

07-10-2018, 13:02

konamiman wrote:
Meits wrote:

But... Are there things you can NOT do as well?

He almost can't write README files. Big smile

Hahahaha!
That's true!

By Huey

Prophet (2642)

Huey's picture

08-10-2018, 14:09

Great work!

I've spend already quite some time reading the code and going through the structures.

By Guillian

Prophet (3164)

Guillian's picture

08-10-2018, 15:51

Thanks, Huey!
I hope you will find it interesting.

By Giangiacomo Zaffini 2

Expert (73)

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08-10-2018, 16:49

I tested it, if I'm not mistaken, sjasm 0.39c compiles codebase but sjasm 0.42c does not compile.

It is quite a feeling having such Metal Gear compiled in a second after enter key smashed. Cool

By iamweasel2

Champion (485)

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09-10-2018, 05:41

This is amazing ! Thanks very much for this great work ! Smile

If I may suggest, it would be nice a full dissassembly of a small classic MSX game (16 k). Anyone would do: Hyper Rally, King's valley, Hero, River Raid etc... It would help a lot for people learning asm if they could understand how to code a small msx action game.

By theNestruo

Expert (66)

theNestruo's picture

09-10-2018, 06:47

Thank you, Manuel!!!
I love reading code to discover different approaches and alternative solutions, and usually to improve my own code.
It's great to study how Konami did some things (such as reading input; much easier than what I was trying to do!).

iamweasel2 wrote:

If I may suggest, it would be nice a full dissassembly of a small classic MSX game (16 k). Anyone would do: Hyper Rally, King's valley, Hero, River Raid etc... It would help a lot for people learning asm if they could understand how to code a small msx action game.

Does Pyramid Warp (T&E, 1983) qualify? https://github.com/theNestruo/msx-pyramidwarpex

By Guillian

Prophet (3164)

Guillian's picture

09-10-2018, 09:55

@Giangiacomo The sources compile with sjasm 0.39 as explained in the readme. But it is possible to adapt them to work with 0.42 (Fernando García aka Bitvision did it)

@iamweasel2 Perhaps in a future I'll release more sources/disassemblies (King's Valley, Knight Lore, etc.)

@theNestruo It is nice to hear that the sources are helping to improve your game!

By Manuel

Ascended (14667)

Manuel's picture

09-10-2018, 21:20

Guillian: just wondering: of that 128kB, how much is code, how much is data? And how is the data divided? I guess mostly graphics and map data. Any idea of how much of each?

By Sandy Brand

Expert (117)

Sandy Brand's picture

10-10-2018, 00:11

Wow! That is some really impressive retro archeology! Smile

By Guillian

Prophet (3164)

Guillian's picture

10-10-2018, 09:00

Manuel: a rough estimation could be about 36 kB of code, 16 kB of sprites, 8 kB of music/sfx, 6 kB of text, 32 kB of graphics, 10 kB of rooms, 10 kB of metaTiles, 10 kB other data.

By Manuel

Ascended (14667)

Manuel's picture

10-10-2018, 22:21

Thanks Smile Interesting!

By Edevaldo

Resident (61)

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12-10-2018, 05:14

Quote:

Manuel: a rough estimation could be about 36 kB of code, 16 kB of sprites, 8 kB of music/sfx, 6 kB of text, 32 kB of graphics, 10 kB of rooms, 10 kB of metaTiles, 10 kB other data.

I was very curious about that as well. Thanks!

Could you comment on your disassemble process? I would like to try it on a simpler game.

By theNestruo

Expert (66)

theNestruo's picture

12-10-2018, 11:41

I'm used to use zero flag (z) for true/false return values, and I can see that carry flag (c) is widely used here.
Is it usual in Z80 assembler to use C for that purpose? Is my BASIC and C background tricking me to think in terms of Z/NZ?

By Guillian

Prophet (3164)

Guillian's picture

12-10-2018, 14:34

Edevaldo wrote:

Could you comment on your disassemble process? I would like to try it on a simpler game.

Probably it is easier to show it on a video that explain it. It can be done in different ways:

- 1st pass: disassembly, analyze and annotate the flow of the program
- 2nd pass: fix the parts that were wrongly identified

Or:
- 1st pass: Fully disassembly the code
- 2nd pass: Analyze and annotate the code
- 3rd pass: Fixes

theNestruo wrote:

I'm used to use zero flag (z) for true/false return values, and I can see that carry flag (c) is widely used here.
Is it usual in Z80 assembler to use C for that purpose? Is my BASIC and C background tricking me to think in terms of Z/NZ?

It depends on what you need to check. I.e.: checking threshold values, or if a value in within a range, the C and NC are better choices.

By ren

Paragon (1154)

ren's picture

12-10-2018, 16:39

Guillian wrote:

I could do the same with other games, but... not really sure if it is worth the effort.

May I ask you how long you've been working on this disassemble?

Some n00b questions from me.. Murdoch I now very little (to nothing) about assembly language, but I reckon having it disassembled says (to an extend) nothing about any higher level language the programmers might have used, right? Or are there any conclusion you can draw based on what you've seen/come across?

I wonder to what extend the structure you present the disassemble in, also represents the source structure Konami employed? High probability, or some guesses/own interpretations here & there?

Cheers / thanks for illuminating! Smile

By iamweasel2

Champion (485)

iamweasel2's picture

12-10-2018, 16:57

theNestruo wrote:

Thank you, Manuel!!!
I love reading code to discover different approaches and alternative solutions, and usually to improve my own code.
It's great to study how Konami did some things (such as reading input; much easier than what I was trying to do!).

iamweasel2 wrote:

If I may suggest, it would be nice a full dissassembly of a small classic MSX game (16 k). Anyone would do: Hyper Rally, King's valley, Hero, River Raid etc... It would help a lot for people learning asm if they could understand how to code a small msx action game.

Does Pyramid Warp (T&E, 1983) qualify? https://github.com/theNestruo/msx-pyramidwarpex

Of course it qualifies ! :) Thanks very much theNestruo, I'll check it out. :)

By Guillian

Prophet (3164)

Guillian's picture

12-10-2018, 20:44

ren wrote:

May I ask you how long you've been working on this disassemble?

I disassembled the game and analyzed it in two months one year ago.
Then two months ago I started adding annotations.
So it took me about 4 months in my spare time.

ren wrote:

Some n00b questions from me.. Murdoch I now very little (to nothing) about assembly language, but I reckon having it disassembled says (to an extend) nothing about any higher level language the programmers might have used, right? Or are there any conclusion you can draw based on what you've seen/come across?

I'm almost 100% sure that the game was programmed in assembler.

ren wrote:

I wonder to what extend the structure you present the disassemble in, also represents the source structure Konami employed? High probability, or some guesses/own interpretations here & there?

I have no idea how Konami structured the code. But I know they reused different "modules", that probably they included/imported into different projects (i.e.: the code for the Konami logo, for reading and storing the controls, for calculating the trajectory/speed of a shot, etc.)

The main structure in all Konami games is almost the same, except in some of them that were not really made by Konami (i.e: Contra, or Green Beret)

By MOA

Champion (288)

MOA's picture

16-10-2018, 00:56

Wow, very well done!

This was definitely written in assembly by the Konami coders; no compiler would generate such code. Code quality is actually very decent; much better than I would expect from a company trying to make money, hehe.

By Wolverine_nl

Paladin (938)

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16-10-2018, 09:22

MOA wrote:

Wow, very well done!

This was definitely written in assembly by the Konami coders; no compiler would generate such code. Code quality is actually very decent; much better than I would expect from a company trying to make money, hehe.

Unlike some nowadays, that release a game which isn't a 100% finished game yet. And you get an update every other day. oO
The old days, games needed to be 100% working. Smile

By Grauw

Enlighted (7407)

Grauw's picture

16-10-2018, 09:42

theNestruo wrote:

I'm used to use zero flag (z) for true/false return values, and I can see that carry flag (c) is widely used here.
Is it usual in Z80 assembler to use C for that purpose? Is my BASIC and C background tricking me to think in terms of Z/NZ?

I use both as is convenient, but I prefer carry as it's easier to set explicitly (scf/ccf/and a), is modified by less instructions (e.g. inc & bit don't), and is easier to use directly in math (e.g. sbc a,a); with the zero flag you always need to branch.

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