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by JonChesterfield 803 days ago
In fairness it wasn't Apple who implemented the non-mac uses of their hardware.

AMD's driver is in your kernel, all the userspace is on GitHub. The ISA is documented. It's entirely possible to treat the ASICs as mass market subsidized floating point machines and run your own code on them.

Modulo firmware. I'm vaguely on the path to working out what's going on there. Changing that without talking to the hardware guys in real time might be rather difficult even with the code available though.
1 comments
imtringued 802 days ago
You are ignoring that AMD doesn't use an intermediate representation and every ROCm driver is basically compiling to a GPU specific ISA. It wouldn't surprise me that there are bugs they have fixed for one ISA that they didn't bother porting to the others. The other problem is that most likely their firmware contains classic C bugs like buffer overflows, undefined behaviour, or stuff like deadlocks.
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JonChesterfield 802 days ago
This is sort of true. Graphics compiles to spir-v, moves that around as deployment, then runs it through llvm to create the compiled shaders. Compute doesn't bother with spir-v (to the distress of some of our engineers) and moves llvm IR around instead. That goes through the llvm backend which does mostly the same stuff for each target machine. There probably are some bugs that were fixed on one machine and accidentally missed on another - the compiler is quite branchy - but it's nothing like as bad as a separate codebase per ISA. Nvidia has a specific ISA per card too, they just expose PTX and SASS as abstractions over it.

I haven't found the firmware source code yet - digging through confluence and perforce tries my patience and I'm supposed to be working on llvm - but I hear it's written in assembly, where one of the hurdles to open sourcing it is the assembler is proprietary. I suspect there's some common information shared with the hardware description language (tcl and verilog or whatever they're using). To the extent that turns out to be true, it'll be immune to C style undefined behaviour, but I wouldn't bet on it being free from buffer overflows.

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