RFC: Porting ROCm to FreeBSD

[Yohello1]

Hello, I'm an intern at the FreeBSD Foundation working with Ed Maste to port ROCm to FreeBSD.

So far we've been able to successfully compile rocr-runtime, and verified that rocminfo runs without errors, and outputs ROCk module is NOT loaded, possibly no GPU devices, then gracefully exits.

We've also gotten one patch merged into ROCM/llvm-project to clear compiler blocks on the toolchain side.

As of now, I am working on cleaning up and refactoring my local patches to rocr-runtime to upstream them in bite-sized pieces. Concurrently, we are working to re-enable amdkfd within FreeBSD's native amdgpu driver port, updating it to match Linux kernel version 6.18.4. We are currently testing this on a Framework Desktop powered by a Strix Halo APU, where hardware support was stabilized in the 6.18.x kernel series.

The patchset is still a work in progress, and I am still parsing through it to extract clean commits. But I wanted to reach out to the systems architects here to ask; What is the preferred architectural pattern for introducing a new operating system target to rocr-runtime?

I have noticed the existing os_t enums and scattered platform checks in CMakeLists.txt. When introducing large platform specific overrides (like OS memory mapping, and threading wrappers), is it better to encapsulate these into entirely separate files (i.e a separate os_freebsd.cpp), or extending existing files via preprocessor macros.

[Yohello1]

@dayatsin-amd @kentrussell Sorry to bug you guys again, but I have two questions about adding in new platforms;

1. Should I care about the current_os variable? It's never called

 siracha   users/Yohello1/libhsakmt-types-change ?:1  ~/code/rocm-systems/projects/rocr-runtime  grep -R current_os
runtime/hsa-runtime/core/runtime/runtime.cpp:  // extensions_.LoadFinalizer(kFinalizerLib[os_index(os::current_os)]);
runtime/hsa-runtime/core/util/os.h:static const os_t current_os = os_t::OS_WIN;
runtime/hsa-runtime/core/util/os.h:static const os_t current_os = os_t::OS_LINUX;
 siracha   users/Yohello1/libhsakmt-types-change ?:1  ~/code/rocm-systems/projects/rocr-runtime  

2. Im going to need to add in a file called rocr-runtime/libhsakmt/include/hsakmt/freebsd/kfd_ioctl.h which is pretty big, and is going to involve me editing the rocr-runtime/libhsakmt/CMakeLists.txt so the correct header gets included at compile time. Is there a preferred method for adding in the os conditions, or should I just go with what seems correct? As of now Im just going to add in 3~ if/ifelse conditions depending on whether your on Linux or FreeBSD on what to include