7 ms·

Patching MechCommander's "left arm bug" for fun and profit

92 points by Narann 2mo ago

derac 2mo ago
This is cool, maybe "target left arm" implies that it's your left, when targetting them and you're facing each other. So, their right arm.
- derac 2mo ago
  Btw, I recently did my first patches with ghidra. Is there any way to avoid jumping into a code cave by shifting all the instructions up then updating any statements referring to those memory locations? Seems like it should be simple enoigh in theory, but I didn't find an implementation on a cursory search. Could probably code up a plugin pretty easily.
  - BobbyTables2 2mo ago
    How can you be dead certain that all references are known in Ghidra? Just non-disassembled function or unidentified struct would ruin your plans…
  - ACCount37 2mo ago
    It's basically re-linking the executable. Way too easy to shoot foot - miss one reference and things break in a spectacular, or, worse, subtle fashion. Which means: you definitely need to know where all the references are and what they point to. References are under no obligation to be presented in a sensible, decompiler-friendly way. Which is why "jump out into the patch, jump back in" is such a staple of patching. The other way is the hard way, full of pitfalls and potential issues.
    - derac 2mo ago
      Thanks for this explanation!
20k 2mo ago
Oh man this was my biggest pet peeve with mechcommander as a kid, thanks for fixing it!
pkhuong 2mo ago
If you need a compact byte -> bit lookup table on x86, consider using the memory form of the bit test (BT) instruction.
golden-face 2mo ago
Great writeup! Vividly remember this being a thing especially in multiplayer. What was that janky match matching service, MSN something? Also a really underrated game, the mechanics (line of sight over the horizon stuff) and isometric graphics were pretty cool for the time and it had a well developed story/campaign mode.
- deleted 2mo ago
  [deleted]
- CincinnatiMan 2mo ago
  Mplayer maybe?
- officeplant 2mo ago
  gamespy flash backs for me.
protocolture 2mo ago
I really need to put some of these techniques to the test with Metal Fatigue.
- tangenter 2mo ago
  A rare gem to see someone talking about MF. I used to play lots of it with friends, our games would last for over 48 hours (we wouldn’t sleep). Different time.
  - protocolture 2mo ago
    My games would last until whoever was hosting had the bug that kills the game due to having too many units, or running out of names for pilots. And it was somehow still incredibly satisfying, even though there was probably just one bugger who went underground at the start and all the people who over invested in giant robots would have to play whack a mole to find him.
tangenter 2mo ago
I wish they would release MC1 source the way they did with MC2.
Night_Thastus 2mo ago
Now let's see this working for Darkest Hours. ;) (Assuming they didn't fix it themselves, it is a pretty big overhaul to MC1) 99% sure it should work fine for (Exodus and Turncoat), (X-Ray and DSC Raid), and (Xenocide and Bengal Lancers) since those are just custom campaigns. Lovely stuff. Always a joy to see anything MechWarrior related end up here on HN.
- MHLoppy 2mo ago
  As far as I know even DH is still only modifying the game at the data files level, not the "actual code" level (with the exclusion of the resolution edits). So probably the fix for the left arm bug will work fine for DH or any of RizZen's other campaigns, but because of the new weapons I wouldn't bother using the weapon classification fix unless you revise the fix to match the modded weapons (which is unlikely to be worth the effort tbh).
blobbers 2mo ago
I never played this game! I didn't realize there was a RTS after Crescent Hawk's revenge. I'm looking at the MC2 source code now... it looks like there is a Linux port, meaning could probably get it working for Apple using Fable 5, AI haters, I will challenge you to a batchall.
- officeplant 2mo ago
  >probably get it working for Apple I've gotten older games running just fine with Whisky/game porting toolkit. Sometimes you also need something to fix old DirectX issues like dgvoodoo2. If you want to make it even easier you could try loading it via Heroic Launcher which supports game porting toolkit. (Do note: whisky.app is out of development now that the Dev quit to do being pestered by the community so much)
toast0 2mo ago
I wonder if the board game materials have rules or guidance about where equipment goes? I dunno how close the computer games stick to the board game materials though.
- murderfs 2mo ago
  The board game has extensive rules on mech design, but for weapons, it's just wherever they'll fit. Some of the built-in hardware has fixed locations: cockpit, life support, sensors go in the head; engines go in the center torso (with light and xtralight fusion engines spilling out into the side torsos as well), arm and hand actuators go in the arms, and hip, leg, and foot actuators go in the legs. You can see this in the critical slot section in a record sheet: https://i.redd.it/jt3p2f1v14gf1.jpeg https://i.redd.it/jt3p2f1v14gf1.jpeg This one definitely deviates from tabletop: pretty much everything except the smallest weapons have an integral tonnage, and the weapons themselves don't line up directly with their tabletop versions. The newer games tend to be absolutely consistent with the mech design rules in terms of what weapons are available, and their weights and sizes, such that board game designs are legal in the game (and usually the state you get the mechs in before you customize them), and customized mechs are legal board game designs. They tend to limit the customization by doing things like having mechs have predefined hardpoints that limit what types/sizes of guns can go where, because otherwise you just end up with every mech being identical, with maximum armor and the rest of the tonnage being spent on whatever happens to be the most optimal weapon.
iamacyborg 2mo ago
Dear god I loved this game when it came out. It was hard.
- protocolture 2mo ago
  I remember it taking me ages to complete the demo missions. And once I had, there being tons of replay value just in the demo missions.
  - iamacyborg 2mo ago
    That damned Vulture in the base in the second demo mission was rough. I hit a serious wall in the campaign in Op1M5 when you had to defend the farm. It’s almost a shame that MC2 is so easy in comparison
    - efromvt 2mo ago
      Op1M5 was scarring the first (dozen) time around! Thank you minelayers
      - iamacyborg 2mo ago
        Yeah I had to go back to M3 to salvage the madcat before I was able to finally get past it
- deleted 2mo ago
  [deleted]
close04 2mo ago
It just hit me, in 2026, that MeshCommander [1] (the Intel AMT remote management tool) is probably a homage naming after MechCommander. Came here excited that MeshCommander is maintained again. [1] https://github.com/Ylianst/MeshCommander https://github.com/Ylianst/MeshCommander
notrealyme123 2mo ago
A bit off topic, but a very nice niche YouTubers "SardonicSays" posted a great Retrospective about MechCommander yesterday. https://www.youtube.com/watch?v=8CVvOWlfl1U https://www.youtube.com/watch?v=8CVvOWlfl1U
- deleted 2mo ago
  [deleted]
efromvt 2mo ago
I wonder if all those different heavy shenanigans are just to get the hollander's gauss/hunchback autoconnon in the right torso by default. (original Mechcommander is still the best of the series, even if mission 5 broke my soul for awhile).
srean 2mo ago
I have forever been confused by 'left' and 'right'. It takes me a few seconds of deliberate thinking to get it right. So in one of my first piece of software that I wrote for real money I had two functions. One called create_scene_left(), the other called create_scene_rght(). I was very pleased with myself for sneaking in creating_a_scene, but the left and right versions did the opposite of what their names indicated. Users of the software had no problems, but I am sure it would confuse any maintainer. It even took me an year to even realize that the names were wrong.
M95D 2mo ago
> Mantis targets 64-bit Windows systems and requires .NET 8 or higher to run. So, it won't work on the same retro PC as the game.
- MHLoppy 2mo ago
  In my experience it was not that hard (as far as 25 year old games go) to get running on a Windows 10 system, which is what I played MC1 on and made Mantis on. I wrote down the steps I used[1] but there are alternative approaches using e.g., dgVoodoo which are not hard to find if you search for them. As far as I'm aware there's no need to use a retro system to reliably run MC1. If you are for some reason intent on playing MC1 on a retro rather than modern system, Mantis is just a glorified automated hex editor and you can byte-for-byte replicate what it does to the game exe by copy-pasting the hex edits which are already outlined in the OP (for the bug fixes) and elsewhere (for the rest of what Mantis does). --- [1] https://mhloppy.com/2026/04/mechcommander-windows-10-without-crashes/ https://mhloppy.com/2026/04/mechcommander-windows-10-without...
  - M95D 2mo ago
    I was just noticing that there was a whole lot of work fixing these minor bugs, and then went all lazy writing the patch... Or maybe I was spoiled by decades of scene patches, cracks and tiny demos with chiptune music and funny graphics.
    - MHLoppy 2mo ago
      There is a certain irony I guess, but in my eyes the "patch" is the hex edits, not Mantis. If I had published these fixes but never gone back and made Mantis, I would still have considered the work "complete". Mantis was made nearly one month after the actual patching was done partly as an excuse to test out a few things like the build settings available in newer .NET releases (e.g., framework-dependent vs self-contained build with trimming, JIT vs AoT vs ReadyToRun compilation). It wasn't really laziness to target .NET 8 because exploring those build options made it take longer than just building using e.g., .NET Framework since Mantis is so basic. As I said, glorified automated hex editor.

92 points by Narann 2mo ago

derac 2mo ago

This is cool, maybe "target left arm" implies that it's your left, when targetting them and you're facing each other. So, their right arm.

derac 2mo ago
Btw, I recently did my first patches with ghidra. Is there any way to avoid jumping into a code cave by shifting all the instructions up then updating any statements referring to those memory locations? Seems like it should be simple enoigh in theory, but I didn't find an implementation on a cursory search. Could probably code up a plugin pretty easily.
- BobbyTables2 2mo ago
  How can you be dead certain that all references are known in Ghidra? Just non-disassembled function or unidentified struct would ruin your plans…
- ACCount37 2mo ago
  It's basically re-linking the executable. Way too easy to shoot foot - miss one reference and things break in a spectacular, or, worse, subtle fashion. Which means: you definitely need to know where all the references are and what they point to. References are under no obligation to be presented in a sensible, decompiler-friendly way. Which is why "jump out into the patch, jump back in" is such a staple of patching. The other way is the hard way, full of pitfalls and potential issues.
  - derac 2mo ago
    Thanks for this explanation!

20k 2mo ago

Oh man this was my biggest pet peeve with mechcommander as a kid, thanks for fixing it!

pkhuong 2mo ago

If you need a compact byte -> bit lookup table on x86, consider using the memory form of the bit test (BT) instruction.

golden-face 2mo ago

Great writeup! Vividly remember this being a thing especially in multiplayer. What was that janky match matching service, MSN something? Also a really underrated game, the mechanics (line of sight over the horizon stuff) and isometric graphics were pretty cool for the time and it had a well developed story/campaign mode.

deleted 2mo ago
[deleted]
CincinnatiMan 2mo ago
Mplayer maybe?
officeplant 2mo ago
gamespy flash backs for me.

protocolture 2mo ago

I really need to put some of these techniques to the test with Metal Fatigue.

tangenter 2mo ago
A rare gem to see someone talking about MF. I used to play lots of it with friends, our games would last for over 48 hours (we wouldn’t sleep). Different time.
- protocolture 2mo ago
  My games would last until whoever was hosting had the bug that kills the game due to having too many units, or running out of names for pilots. And it was somehow still incredibly satisfying, even though there was probably just one bugger who went underground at the start and all the people who over invested in giant robots would have to play whack a mole to find him.

tangenter 2mo ago

I wish they would release MC1 source the way they did with MC2.

Night_Thastus 2mo ago

Now let's see this working for Darkest Hours. ;) (Assuming they didn't fix it themselves, it is a pretty big overhaul to MC1) 99% sure it should work fine for (Exodus and Turncoat), (X-Ray and DSC Raid), and (Xenocide and Bengal Lancers) since those are just custom campaigns. Lovely stuff. Always a joy to see anything MechWarrior related end up here on HN.

MHLoppy 2mo ago
As far as I know even DH is still only modifying the game at the data files level, not the "actual code" level (with the exclusion of the resolution edits). So probably the fix for the left arm bug will work fine for DH or any of RizZen's other campaigns, but because of the new weapons I wouldn't bother using the weapon classification fix unless you revise the fix to match the modded weapons (which is unlikely to be worth the effort tbh).

blobbers 2mo ago

I never played this game! I didn't realize there was a RTS after Crescent Hawk's revenge. I'm looking at the MC2 source code now... it looks like there is a Linux port, meaning could probably get it working for Apple using Fable 5, AI haters, I will challenge you to a batchall.

officeplant 2mo ago
>probably get it working for Apple I've gotten older games running just fine with Whisky/game porting toolkit. Sometimes you also need something to fix old DirectX issues like dgvoodoo2. If you want to make it even easier you could try loading it via Heroic Launcher which supports game porting toolkit. (Do note: whisky.app is out of development now that the Dev quit to do being pestered by the community so much)

toast0 2mo ago

I wonder if the board game materials have rules or guidance about where equipment goes? I dunno how close the computer games stick to the board game materials though.

murderfs 2mo ago
The board game has extensive rules on mech design, but for weapons, it's just wherever they'll fit. Some of the built-in hardware has fixed locations: cockpit, life support, sensors go in the head; engines go in the center torso (with light and xtralight fusion engines spilling out into the side torsos as well), arm and hand actuators go in the arms, and hip, leg, and foot actuators go in the legs. You can see this in the critical slot section in a record sheet: https://i.redd.it/jt3p2f1v14gf1.jpeg https://i.redd.it/jt3p2f1v14gf1.jpeg This one definitely deviates from tabletop: pretty much everything except the smallest weapons have an integral tonnage, and the weapons themselves don't line up directly with their tabletop versions. The newer games tend to be absolutely consistent with the mech design rules in terms of what weapons are available, and their weights and sizes, such that board game designs are legal in the game (and usually the state you get the mechs in before you customize them), and customized mechs are legal board game designs. They tend to limit the customization by doing things like having mechs have predefined hardpoints that limit what types/sizes of guns can go where, because otherwise you just end up with every mech being identical, with maximum armor and the rest of the tonnage being spent on whatever happens to be the most optimal weapon.

iamacyborg 2mo ago

Dear god I loved this game when it came out. It was hard.

protocolture 2mo ago
I remember it taking me ages to complete the demo missions. And once I had, there being tons of replay value just in the demo missions.
- iamacyborg 2mo ago
  That damned Vulture in the base in the second demo mission was rough. I hit a serious wall in the campaign in Op1M5 when you had to defend the farm. It’s almost a shame that MC2 is so easy in comparison
  - efromvt 2mo ago
    Op1M5 was scarring the first (dozen) time around! Thank you minelayers
    - iamacyborg 2mo ago
      Yeah I had to go back to M3 to salvage the madcat before I was able to finally get past it
deleted 2mo ago
[deleted]

close04 2mo ago

It just hit me, in 2026, that MeshCommander [1] (the Intel AMT remote management tool) is probably a homage naming after MechCommander. Came here excited that MeshCommander is maintained again. [1] https://github.com/Ylianst/MeshCommander https://github.com/Ylianst/MeshCommander

notrealyme123 2mo ago

A bit off topic, but a very nice niche YouTubers "SardonicSays" posted a great Retrospective about MechCommander yesterday. https://www.youtube.com/watch?v=8CVvOWlfl1U https://www.youtube.com/watch?v=8CVvOWlfl1U

deleted 2mo ago
[deleted]

efromvt 2mo ago

I wonder if all those different heavy shenanigans are just to get the hollander's gauss/hunchback autoconnon in the right torso by default. (original Mechcommander is still the best of the series, even if mission 5 broke my soul for awhile).

srean 2mo ago

I have forever been confused by 'left' and 'right'. It takes me a few seconds of deliberate thinking to get it right. So in one of my first piece of software that I wrote for real money I had two functions. One called create_scene_left(), the other called create_scene_rght(). I was very pleased with myself for sneaking in creating_a_scene, but the left and right versions did the opposite of what their names indicated. Users of the software had no problems, but I am sure it would confuse any maintainer. It even took me an year to even realize that the names were wrong.

M95D 2mo ago

> Mantis targets 64-bit Windows systems and requires .NET 8 or higher to run. So, it won't work on the same retro PC as the game.

MHLoppy 2mo ago
In my experience it was not that hard (as far as 25 year old games go) to get running on a Windows 10 system, which is what I played MC1 on and made Mantis on. I wrote down the steps I used[1] but there are alternative approaches using e.g., dgVoodoo which are not hard to find if you search for them. As far as I'm aware there's no need to use a retro system to reliably run MC1. If you are for some reason intent on playing MC1 on a retro rather than modern system, Mantis is just a glorified automated hex editor and you can byte-for-byte replicate what it does to the game exe by copy-pasting the hex edits which are already outlined in the OP (for the bug fixes) and elsewhere (for the rest of what Mantis does). --- [1] https://mhloppy.com/2026/04/mechcommander-windows-10-without-crashes/ https://mhloppy.com/2026/04/mechcommander-windows-10-without...
- M95D 2mo ago
  I was just noticing that there was a whole lot of work fixing these minor bugs, and then went all lazy writing the patch... Or maybe I was spoiled by decades of scene patches, cracks and tiny demos with chiptune music and funny graphics.
  - MHLoppy 2mo ago
    There is a certain irony I guess, but in my eyes the "patch" is the hex edits, not Mantis. If I had published these fixes but never gone back and made Mantis, I would still have considered the work "complete". Mantis was made nearly one month after the actual patching was done partly as an excuse to test out a few things like the build settings available in newer .NET releases (e.g., framework-dependent vs self-contained build with trimming, JIT vs AoT vs ReadyToRun compilation). It wasn't really laziness to target .NET 8 because exploring those build options made it take longer than just building using e.g., .NET Framework since Mantis is so basic. As I said, glorified automated hex editor.