Ship the merged CPU kernels as their own library

[shoumikhin]

The CPU operator kernels are compiled into whichever component links
them. The Python extension therefore carries a full private copy, which makes it large, and a
C++ application cannot get the same operators without building them from source.

before:
  _portable_lib.so     contains its own copy of every CPU kernel
  your C++ app         cannot get them without building from source

after:
  executorch/lib/libexecutorch_optimized_native_cpu_ops_lib.so.1
    _portable_lib.so   -> links it
    your C++ app       -> links it

There is a correctness reason too, not just size. Operators register themselves into a table
when their library loads. Two copies in one process means two independent registrations of the
same operator set, and which one a model resolves to is then a matter of load order.

How you use it

find_package(executorch REQUIRED)
target_link_libraries(my_app PRIVATE executorch::runtime executorch::kernels)

The target name is the contract, not the file name. A model running the usual CPU operators
needs nothing else.

Tested

Built the wheel on Linux x86_64 and aarch64, installed it into a clean environment, and
confirmed by symbol inspection that exactly one shipped library registers the CPU operator set.
Linked a C++ application against the component, ran a model through it, and ran the existing
Python tests so current users are unaffected.

[shoumikhin]

Stack from ghstack (oldest at bottom):

• Check the shipped device code covers the GPUs a wheel claims #21567
• Publish CUDA wheels so a GPU user does not build from source #21569
• Ship the CUDA delegate as its own library #21531
• Ship the XNNPACK delegate as its own library #21526
• -> Ship the merged CPU kernels as their own library #21524
• Ship the thread pool as its own library so a process has one pool #21522
• Ship a linkable shared runtime and make the Python bindings use it #21514

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/21524

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 24 New Failures, 269 Pending, 1 Unrelated Failure, 4 Unclassified Failures

As of commit 4cb6fbb with merge base b5239a5 ():

NEW FAILURES - The following jobs have failed:

• Build Presets / linux (linux, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID 8116:35C64D:5AC3C9:12D6265:6A72A0D7 and timestamp 2026-08-05 02:32:55 UTC. For more on scraping GitHub and how it may affect your rights, please review our Terms of Service (https://docs.github.com/en/site-policy/github-terms/github-terms-of-service) - https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api#rate-limiting
• Build Presets / linux (llm, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID 9A36:34AF96:5BB69E:130A3F3:6A72A0CC and timestamp 2026-08-05 02:32:44 UTC. For more on scraping GitHub and how it may affect your rights, please review our Terms of Service (https://docs.github.com/en/site-policy/github-terms/github-terms-of-service) - https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api#rate-limiting
• Build Presets / linux (pybind, linux.arm64.2xlarge, executorch-ubuntu-22.04-gcc11-aarch64) / build (gh)
  ##[error]API rate limit exceeded for installation. If you reach out to GitHub Support for help, please include the request ID E17A:2EBEB3:5A49C3:12CB26B:6A72A0CE and timestamp 2026-08-05 02:32:46 UTC. For more on scraping GitHub and how it may affect your rights, please review our Terms of Service (https://docs.github.com/en/site-policy/github-terms/github-terms-of-service) - https://docs.github.com/en/rest/using-the-rest-api/getting-started-with-the-rest-api#rate-limiting
• nightly / link-check / lint-urls (gh)
• nightly / link-check / lint-xrefs (gh)
• pull / test-arm-backend-public-api-backward-compatibility / linux-job (gh)
  RuntimeError: Command docker exec -t 456967ffe3df9ac6a4bfd260b995be57285d186ad65905fecb998758d2cf9211 /exec failed with exit code 1
• pull / test-lora-linux / linux-job (gh)
  AttributeError: '_OpNamespace' 'llama' object has no attribute 'sdpa_with_kv_cache'
• pull / test-lora-multimethod-linux / linux-job (gh)
  AttributeError: '_OpNamespace' 'llama' object has no attribute 'sdpa_with_kv_cache'
• pull / test-models-linux (emformer_join, xnnpack-quantization-delegation, linux.4xlarge.memory) / linux-job (gh)
  RuntimeError: Command docker exec -t 8f17bad9318f99544ba6c62c213370b918d40ef204a9fadcad616730f1f5cf8c /exec failed with exit code 1
• pull / test-models-linux (ic4, xnnpack-quantization-delegation, linux.4xlarge.memory) / linux-job (gh)
  RuntimeError: Command docker exec -t a0de0cba3cd3c028b97310c438ad2d849c6c6d584f0f3113876f20be7b13dbef /exec failed with exit code 1
• pull / test-multimodal-linux (gemma3-4b) / linux-job (gh)
  RuntimeError: Command docker exec -t c7f672f804c457366a50577462bf8c3b60848b48d5299efe6b8378956523ef24 /exec failed with exit code 1
• pull / test-phi-3-mini-runner-linux / linux-job (gh)
  AttributeError: '_OpNamespace' 'llama' object has no attribute 'sdpa_with_kv_cache'
• Test CUDA Builds / export-model-cuda-artifact (SocialLocalMobile, Qwen3.5-35B-A3B-HQQ-INT4, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command bash /__w/_temp/exec_script failed with exit code 1
• Test WebGPU Native (Dawn) / test-webgpu-native / linux-job (gh)
  [ FAILED ] WebGPUNative.SdpaAllFamiliesRanWhenDirSet
• trunk / test-arm-backend-ethos-u (test_deit_e2e_ethos_u) / linux-job (gh)
  RuntimeError: Command docker exec -t 6b1cf5385217ba1cf01df6d9ec0c8648bc27329d73e163c14c051e4b9c87fde1 /exec failed with exit code 1
• trunk / test-arm-backend-ethos-u (test_model_smollm2_135M_ethos_u85) / linux-job (gh)
  RuntimeError: Command docker exec -t de7ca6ba629a2ab25213b5fe7383170d1cd2615bea617a620c8d5d748c2a4d84 /exec failed with exit code 1
• trunk / test-arm-backend-ethos-u (test_ootb_tests_ethos_u) / linux-job (gh)
  RuntimeError: Command docker exec -t 3229b31914365ebe868bfd655cfa893cbbf45988ded849afca88da2fd02f6273 /exec failed with exit code 1
• trunk / test-arm-backend-ethos-u (test_ootb_tests_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t ec3225401676ede8505aa289edc145d771c331d512f7511b70af02fe0efc0d3c /exec failed with exit code 1
• trunk / test-huggingface-transformers-xnnpack (gemma3-1b|xnnpack|--quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 94f327b60904b500ce2a0056c6ab9d1e954612bbe5fd9fbf3c4c61242e78cd2b /exec failed with exit code 1
• trunk / test-huggingface-transformers-xnnpack (llama3.2-1b|xnnpack|--quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 4adb016659a74e1af8decd4008c3b13033ce3b354faa68dae4e2c92f32e34388 /exec failed with exit code 1
• trunk / test-huggingface-transformers-xnnpack (qwen3-0.6b|xnnpack|--quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 14670521c21dc42b80e3b0a2c6bafe2fc4dd2febe831e4eee46585e8a68ad0ee /exec failed with exit code 1
• trunk / test-huggingface-transformers-xnnpack (qwen3-1.7b|xnnpack|--quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 42b9b6e5f9d1a5938ebc0ad471a63238a2b38ad0b8ef0d9cc32f02abde41fbdd /exec failed with exit code 1
• trunk / test-huggingface-transformers-xnnpack (smollm2-135m|xnnpack|--quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 6ff40a271f062a2c54464108f75134676dbd6d6035b6deb950271fe9961e71ce /exec failed with exit code 1
• trunk / test-huggingface-transformers-xnnpack (smollm3-3b|xnnpack|--quantize) / linux-job (gh)
  RuntimeError: Command docker exec -t 168555037dbb20b4a6792a54f003930b719a2bdcf1dfcedf5847813e112b1aac /exec failed with exit code 1

UNCLASSIFIED FAILURES - DrCI could not classify the following jobs because the workflow did not run on the merge base. The failures may be pre-existing on trunk or introduced by this PR:

• Build macOS Wheels / pytorch/executorch / build-wheel-py3_14-cpu (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  pyarrow
• Build macOS Wheels / pytorch/executorch / upload / upload-wheel-py3_14-cpu (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  Unable to download artifact(s): Artifact not found
• Build Windows Wheels / pytorch/executorch / build-wheel-py3_14-cpu (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  pyarrow
• Build Windows Wheels / pytorch/executorch / upload / upload-wheel-py3_14-cpu (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  Unable to download artifact(s): Artifact not found

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / unittest-editable / windows / windows-job (gh) (trunk failure)

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