Modules

Kinds

A backend owns identity, extra HWCAP bits, and the tuned kernels. There is no vm_cpu_part() in the base library: the backend probes, then registers VM_CPU_BACKEND. A width module does not register a backend. The core owns the storage type; the module only overrides a slot. See doc/fp16.md.

A feature module contributes sources via VECMAT_MODULE_HOOKS (the same hook the float object libraries call) and may append VECMAT_MODULE_TEST_SOURCES / VECMAT_MODULE_BENCH_SOURCES. It must not append to a backend or width register list. No feature module ships in 0.3.x; the kind exists so 0.4.x can land domain helpers without another loader change.

Layout

A module is a directory with module.cmake. Under the recommended layout that is vendors/<vendor>/<name>/. module.cmake is the only file the top-level build includes. It must set VECMAT_MODULE_KIND. Use CMAKE_CURRENT_LIST_DIR for its own sources.

A backend module:

vendors/arm/cortex-a5x
├── doc
│   └── cortex-a5x.md
├── include
│   └── vecmat_cortex_a5x.h
├── module.cmake
└── src
    ├── a5x.h
    ├── gemm_a53.c
    ├── gemm_a55.c
    ├── probe.c
    ├── register.c
    └── sched.c

A width module:

vendors/arm/fp16
├── doc
│   └── fp16.md
├── include
│   └── vecmat_arm_fp16.h
├── module.cmake
└── src
    ├── arm_fp16.h
    ├── neon.c
    ├── probe.c
    └── register.c

Build

Empty VECMAT_MODULES is the default. With vendors/ checked out under this tree:

cmake -S . -B build -G Ninja \
  -DCMAKE_BUILD_TYPE=Release \
  -DVECMAT_MODULES=arm/fp16 \
  -DVECMAT_RUNTIME_DISPATCH=ON
cmake --build build

If the modules are elsewhere, add -DVECMAT_MODULES_PATH=../vecmat-vendors. VECMAT_MODULES entries are paths relative to vendors/ (or to each VECMAT_MODULES_PATH root). A private vendors tree is the same.

module.cmake appends, depending on kind:

• backend: VECMAT_MODULE_HOOKS (called from vecmat_add_float_objects, once per float width), VECMAT_MODULE_REGISTER_INCLUDES, VECMAT_MODULE_REGISTER_CALLS, and optionally VECMAT_MODULE_TEST_HOOKS, VECMAT_MODULE_TEST_SOURCES, VECMAT_MODULE_BENCH_SOURCES.
• width: the lists for the width it implements (VECMAT_FP16_MODULE_HOOKS, VECMAT_FP16_MODULE_REGISTER_CALLS). Those lists are consumed only by that width's object lib. The module's own module.cmake errors if that width's switch is off. A width module must not append to the backend lists; the loader rejects that.

Test and bench sources live in the vendor tree. The mains do not include a module header. VECMAT_MODULE_TEST_HOOKS runs after the test targets exist and may add the public include dir. Do not define a module macro in the test mains.

Backend registration

The base library keeps this surface for backends:

• vm_backend_register() / VM_CPU_BACKEND — a registered table wins
• vm_backend_builtin() — copy a compiled ISA table and override slots. NEON, SVE, and SVE2 are provided. Returns NULL if that ISA was not compiled.
• vm_cpu_set_note() / vm_cpu_note() — one extra banner line, printed only if set
• vm_backend_modules_register() — test and benchmark hook, generated, not a library export
• VECMAT_FORCE_ISA — override the compiled/runtime pick when no backend is registered

Tests and benchmarks do not include a backend header. They call the generated hook, then vm_cpu_init():

vm_backend_modules_register();
vm_cpu_init();
if (vm_cpu_note())
    printf("%s\n", vm_cpu_note());

With no backends selected, the generated function is empty. A backend that does not match the CPU returns 0 and leaves the builtin table in place. A registered backend wins over VECMAT_FORCE_ISA. The same pointer is idempotent. A table with a missing slot is rejected. VM_BACKEND_MAX is 8.

The descriptor:

Copy the builtin table, then replace the slots this schedule owns. vm_backend_builtin(VM_CPU_NEON) is NULL when NEON was not compiled.

const vm_backend_ops *builtin = vm_backend_builtin(VM_CPU_NEON);
ops = *builtin;
ops.vm_gemm_ukernel = my_ukernel;
ops.quat_mul_ptr = my_quat_mul;
backend.name = "my-backend";
backend.features = VM_CPU_BACKEND;
backend.priority = 100;
backend.ops = &ops;
vm_cpu_set_note("backend my-backend part=...");
return vm_backend_register(&backend);

Float symbols are width-suffixed. Internal functions that both object libs define need the same treatment.

Benchmarks keep the selected/compiled/runtime/precision line. They print vm_cpu_note() on the next line only when a backend set one.

string(APPEND VECMAT_MODULE_REGISTER_INCLUDES "#include <vecmat_cortex_a5x.h>\n")
string(APPEND VECMAT_MODULE_REGISTER_CALLS "    vm_cortex_a5x_register();\n")

Adding a module

1. Add vendors/<vendor>/<name>/ with module.cmake, include/, src/, and doc/<name>.md.
2. In module.cmake, set VECMAT_MODULE_KIND to backend or width.
3. Append the lists for that kind. Do not add an #ifdef to test/test_main.c or test/bench_main.c.
4. For a backend: probe in the module, not in src/features/cpu.c. Build the ops table from vm_backend_builtin() plus overrides. Pass VM_CPU_BACKEND unless the schedule is one of the existing ISA bits.
5. Document the register call and any VECMAT_FORCE_* knobs in the module's own doc.