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0 pointsphire1y ago0 comments

Traditional emulators also recompile games to the target device's native machine code. It just happens dynamically at runtime, hence the name "dynamic recompiler" or "Just In Time recompiler".

This is just a static recompiler or ahead of time recompiler, except instead of directly targeting machine code, it's targeting C/C++ as a type of portable assembly. It basically just looks like a bunch of macros implementing the behaviour of powerpc instructions.

The recompiled result will preform nowhere near as good as a proper manual decompilation project, it's still baking in a huge number of quirks from PowerPC and the compiler they originally used, and will have noticeably worse performance. But, performance will usually be good enough, and it's easy to manually replace any bad code-gen that shows up as a bottleneck in profiles.

And while they did replace a bunch of graphics/audio code, they are still directly emulating a bunch of the original Xbox 360 Kernel and hardware.

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alt2271y ago

As I understand it, standard emulation is not dynamic recompiling or jit, it is emulating and converting system calls in realtime. So the game calls a system function unique to the original platform, the emulator sees that call and makes a similar one (or multiple) in the language of the emulating system, and then returns the correct response back to the original call from the game.

I dont think it is compiling anything here.

perching_aix1y ago

Your understanding is incorrect. Applications (games) written for older gaming consoles all had to ship some native code, and were even typically entirely native code. These consoles were also typically not x86 or x86-64 based, so for a PC-targeting emulator to run applications written for these platforms, they do need to have recompiler or interpreter facilities.

They also do not necessarily need to hook and replicate syscalls, provided the user provides a dump of the system software (they just run the system software and make it load the game - the original syscall codes are then ran).

This extends even to the graphics hardware side once programmable shaders became a thing.

alt2271y ago

Thanks for the explanation

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0 pointsphire1y ago0 comments

Traditional emulators also recompile games to the target device's native machine code. It just happens dynamically at runtime, hence the name "dynamic recompiler" or "Just In Time recompiler".

And while they did replace a bunch of graphics/audio code, they are still directly emulating a bunch of the original Xbox 360 Kernel and hardware.

0 comments

alt2271y ago

I dont think it is compiling anything here.

perching_aix1y ago

This extends even to the graphics hardware side once programmable shaders became a thing.

alt2271y ago

Thanks for the explanation

j / k navigate · click thread line to collapse