Kernels in tract-linalg are built using templated assembly and via extern "C" calling conventions.
The templates are stored in linalg/$arch, and in general the file
and main entrypoint share name stem. However, the proc name has a
suffix based on the package version. In order to skip maintaining this
the extern_kernel! macro declares the matching function and
re-exports it sans suffix.
Kernels work like a VM. When dispatching a kernel there's a list of
instructions from FusedKerSpec that's dispatched in a jump
table. For example; as of writing a MatMatmUl is roughly encoded as
[Clear, AddMatMul, Store, Done]. The dispatch is called non_linear_loop.
When iterating on assembly; building the code and looking at the
generated assembly under
target/debug/build/tract-linalg-***/out/fma_mmm_*.S can be much
easier than tracking the flow through each macro.
If one needs to debug a kernel a useful workflow is to simply insert a
mov rNN, [0] at the appropriate point, and configure GDB with
handle SIGSEGV stop nopass. This'll pause in GDB but not send the
signal to the program.