| ===================== |
| Clang Offload Bundler |
| ===================== |
| |
| .. contents:: |
| :local: |
| |
| .. _clang-offload-bundler: |
| |
| Introduction |
| ============ |
| |
| For heterogeneous single source programming languages, use one or more |
| ``--offload-arch=<target-id>`` Clang options to specify the target IDs of the |
| code to generate for the offload code regions. |
| |
| The tool chain may perform multiple compilations of a translation unit to |
| produce separate code objects for the host and potentially multiple offloaded |
| devices. The ``clang-offload-bundler`` tool may be used as part of the tool |
| chain to combine these multiple code objects into a single bundled code object. |
| |
| The tool chain may use a bundled code object as an intermediate step so that |
| each tool chain step consumes and produces a single file as in traditional |
| non-heterogeneous tool chains. The bundled code object contains the code objects |
| for the host and all the offload devices. |
| |
| A bundled code object may also be used to bundle just the offloaded code |
| objects, and embedded as data into the host code object. The host compilation |
| includes an ``init`` function that will use the runtime corresponding to the |
| offload kind (see :ref:`clang-offload-kind-table`) to load the offload code |
| objects appropriate to the devices present when the host program is executed. |
| |
| :program:`clang-offload-bundler` is located in |
| `clang/tools/clang-offload-bundler`. |
| |
| .. code-block:: console |
| |
| $ clang-offload-bundler -help |
| OVERVIEW: A tool to bundle several input files of the specified type <type> |
| referring to the same source file but different targets into a single |
| one. The resulting file can also be unbundled into different files by |
| this tool if -unbundle is provided. |
| |
| USAGE: clang-offload-bundler [options] |
| |
| OPTIONS: |
| |
| Generic Options: |
| |
| --help - Display available options (--help-hidden for more) |
| --help-list - Display list of available options (--help-list-hidden for more) |
| --version - Display the version of this program |
| |
| clang-offload-bundler options: |
| |
| --### - Print any external commands that are to be executed instead of actually executing them - for testing purposes. |
| --allow-missing-bundles - Create empty files if bundles are missing when unbundling. |
| --bundle-align=<uint> - Alignment of bundle for binary files |
| --check-input-archive - Check if input heterogeneous archive is valid in terms of TargetID rules. |
| --inputs=<string> - [<input file>,...] |
| --list - List bundle IDs in the bundled file. |
| --outputs=<string> - [<output file>,...] |
| --targets=<string> - [<offload kind>-<target triple>,...] |
| --type=<string> - Type of the files to be bundled/unbundled. |
| Current supported types are: |
| i - cpp-output |
| ii - c++-cpp-output |
| cui - cuda/hip-output |
| d - dependency |
| ll - llvm |
| bc - llvm-bc |
| s - assembler |
| o - object |
| a - archive of bundled files |
| gch - precompiled-header |
| ast - clang AST file |
| --unbundle - Unbundle bundled file into several output files. |
| |
| Usage |
| ===== |
| |
| This tool can be used as follows for bundling: |
| |
| :: |
| |
| clang-offload-bundler -targets=triple1,triple2 -type=ii -inputs=a.triple1.ii,a.triple2.ii -outputs=a.ii |
| |
| or, it can be used as follows for unbundling: |
| |
| :: |
| |
| clang-offload-bundler -targets=triple1,triple2 -type=ii -outputs=a.triple1.ii,a.triple2.ii -inputs=a.ii -unbundle |
| |
| |
| Supported File Formats |
| ====================== |
| |
| Multiple text and binary file formats are supported for bundling/unbundling. See |
| :ref:`supported-file-formats-table` for a list of currently supported input |
| formats. Use the ``File Type`` column to determine the value to pass to the |
| ``--type`` option based on the type of input files while bundling/unbundling. |
| |
| .. table:: Supported File Formats |
| :name: supported-file-formats-table |
| |
| +--------------------------+----------------+-------------+ |
| | File Format | File Type | Text/Binary | |
| +==========================+================+=============+ |
| | CPP output | i | Text | |
| +--------------------------+----------------+-------------+ |
| | C++ CPP output | ii | Text | |
| +--------------------------+----------------+-------------+ |
| | CUDA/HIP output | cui | Text | |
| +--------------------------+----------------+-------------+ |
| | Dependency | d | Text | |
| +--------------------------+----------------+-------------+ |
| | LLVM | ll | Text | |
| +--------------------------+----------------+-------------+ |
| | LLVM Bitcode | bc | Binary | |
| +--------------------------+----------------+-------------+ |
| | Assembler | s | Text | |
| +--------------------------+----------------+-------------+ |
| | Object | o | Binary | |
| +--------------------------+----------------+-------------+ |
| | Archive of bundled files | a | Binary | |
| +--------------------------+----------------+-------------+ |
| | Precompiled header | gch | Binary | |
| +--------------------------+----------------+-------------+ |
| | Clang AST file | ast | Binary | |
| +--------------------------+----------------+-------------+ |
| |
| .. _clang-bundled-code-object-layout-text: |
| |
| Bundled Text File Layout |
| ======================== |
| |
| The text file formats are concatenated with comments that have a magic string |
| and bundle entry ID in between. The BNF syntax to represent a code object |
| bundle file is: |
| |
| :: |
| |
| <file> ::== <bundle> | <bundle> <file> |
| <bundle> ::== <comment> <start> <bundle_id> <eol> <bundle> <eol> |
| <comment> end <bundle_id> <eol> |
| <start> ::== OFFLOAD_BUNDLER_MAGIC_STR__START__ |
| <end> ::== OFFLOAD_BUNDLER_MAGIC_STR__END__ |
| |
| **comment** |
| The symbol used for starting single-line comment in the file type of |
| constituting bundles. E.g. it is ";" for ll ``File Type`` and "#" for "s" |
| ``File Type``. |
| |
| **bundle_id** |
| The :ref:`clang-bundle-entry-id` for the enclosing bundle. |
| |
| **eol** |
| The end of line character. |
| |
| **bundle** |
| The code object stored in one of the supported text file formats. |
| |
| **OFFLOAD_BUNDLER_MAGIC_STR__** |
| Magic string that marks the existence of offloading data i.e. |
| "__CLANG_OFFLOAD_BUNDLE__". |
| |
| .. _clang-bundled-code-object-layout: |
| |
| Bundled Binary File Layout |
| ========================== |
| |
| The layout of a bundled code object is defined by the following table: |
| |
| .. table:: Bundled Code Object Layout |
| :name: bundled-code-object-layout-table |
| |
| =================================== ======= ================ =============================== |
| Field Type Size in Bytes Description |
| =================================== ======= ================ =============================== |
| Magic String string 24 ``__CLANG_OFFLOAD_BUNDLE__`` |
| Number Of Bundle Entries integer 8 Number of bundle entries. |
| 1st Bundle Entry Code Object Offset integer 8 Byte offset from beginning of |
| bundled code object to 1st code |
| object. |
| 1st Bundle Entry Code Object Size integer 8 Byte size of 1st code object. |
| 1st Bundle Entry ID Length integer 8 Character length of bundle |
| entry ID of 1st code object. |
| 1st Bundle Entry ID string 1st Bundle Entry Bundle entry ID of 1st code |
| ID Length object. This is not NUL |
| terminated. See |
| :ref:`clang-bundle-entry-id`. |
| \... |
| Nth Bundle Entry Code Object Offset integer 8 |
| Nth Bundle Entry Code Object Size integer 8 |
| Nth Bundle Entry ID Length integer 8 |
| Nth Bundle Entry ID string 1st Bundle Entry |
| ID Length |
| 1st Bundle Entry Code Object bytes 1st Bundle Entry |
| Code Object Size |
| \... |
| Nth Bundle Entry Code Object bytes Nth Bundle Entry |
| Code Object Size |
| =================================== ======= ================ =============================== |
| |
| .. _clang-bundle-entry-id: |
| |
| Bundle Entry ID |
| =============== |
| |
| Each entry in a bundled code object (see :ref:`clang-bundled-code-object-layout-text` |
| and :ref:`clang-bundled-code-object-layout`) has a bundle entry ID that indicates |
| the kind of the entry's code object and the runtime that manages it. |
| |
| Bundle entry ID syntax is defined by the following BNF syntax: |
| |
| .. code:: |
| |
| <bundle-entry-id> ::== <offload-kind> "-" <target-triple> [ "-" <target-id> ] |
| |
| Where: |
| |
| **offload-kind** |
| The runtime responsible for managing the bundled entry code object. See |
| :ref:`clang-offload-kind-table`. |
| |
| .. table:: Bundled Code Object Offload Kind |
| :name: clang-offload-kind-table |
| |
| ============= ============================================================== |
| Offload Kind Description |
| ============= ============================================================== |
| host Host code object. ``clang-offload-bundler`` always includes |
| this entry as the first bundled code object entry. For an |
| embedded bundled code object this entry is not used by the |
| runtime and so is generally an empty code object. |
| |
| hip Offload code object for the HIP language. Used for all |
| HIP language offload code objects when the |
| ``clang-offload-bundler`` is used to bundle code objects as |
| intermediate steps of the tool chain. Also used for AMD GPU |
| code objects before ABI version V4 when the |
| ``clang-offload-bundler`` is used to create a *fat binary* |
| to be loaded by the HIP runtime. The fat binary can be |
| loaded directly from a file, or be embedded in the host code |
| object as a data section with the name ``.hip_fatbin``. |
| |
| hipv4 Offload code object for the HIP language. Used for AMD GPU |
| code objects with at least ABI version V4 when the |
| ``clang-offload-bundler`` is used to create a *fat binary* |
| to be loaded by the HIP runtime. The fat binary can be |
| loaded directly from a file, or be embedded in the host code |
| object as a data section with the name ``.hip_fatbin``. |
| |
| openmp Offload code object for the OpenMP language extension. |
| ============= ============================================================== |
| |
| **target-triple** |
| The target triple of the code object. See `Target Triple |
| <https://clang.llvm.org/docs/CrossCompilation.html#target-triple>`_. |
| |
| The bundler accepts target triples with or without the optional environment |
| field: |
| |
| ``<arch><sub>-<vendor>-<sys>``, or |
| ``<arch><sub>-<vendor>-<sys>-<env>`` |
| |
| However, in order to standardize outputs for tools that consume bitcode |
| bundles, bundles written by the bundler internally use only the 4-field |
| target triple: |
| |
| ``<arch><sub>-<vendor>-<sys>-<env>`` |
| |
| **target-id** |
| The canonical target ID of the code object. Present only if the target |
| supports a target ID. See :ref:`clang-target-id`. |
| |
| .. _code-object-composition: |
| |
| Bundled Code Object Composition |
| ------------------------------- |
| |
| * Each entry of a bundled code object must have a different bundle entry ID. |
| * There can be multiple entries for the same processor provided they differ |
| in target feature settings. |
| * If there is an entry with a target feature specified as *Any*, then all |
| entries must specify that target feature as *Any* for the same processor. |
| |
| There may be additional target specific restrictions. |
| |
| .. _compatibility-bundle-entry-id: |
| |
| Compatibility Rules for Bundle Entry ID |
| --------------------------------------- |
| |
| A code object, specified using its Bundle Entry ID, can be loaded and |
| executed on a target processor, if: |
| |
| * Their offload kinds are the same. |
| * Their target triples are compatible. |
| * Their Target IDs are compatible as defined in :ref:`compatibility-target-id`. |
| |
| .. _clang-target-id: |
| |
| Target ID |
| ========= |
| |
| A target ID is used to indicate the processor and optionally its configuration, |
| expressed by a set of target features, that affect ISA generation. It is target |
| specific if a target ID is supported, or if the target triple alone is |
| sufficient to specify the ISA generation. |
| |
| It is used with the ``-mcpu=<target-id>`` and ``--offload-arch=<target-id>`` |
| Clang compilation options to specify the kind of code to generate. |
| |
| It is also used as part of the bundle entry ID to identify the code object. See |
| :ref:`clang-bundle-entry-id`. |
| |
| Target ID syntax is defined by the following BNF syntax: |
| |
| .. code:: |
| |
| <target-id> ::== <processor> ( ":" <target-feature> ( "+" | "-" ) )* |
| |
| Where: |
| |
| **processor** |
| Is a the target specific processor or any alternative processor name. |
| |
| **target-feature** |
| Is a target feature name that is supported by the processor. Each target |
| feature must appear at most once in a target ID and can have one of three |
| values: |
| |
| *Any* |
| Specified by omitting the target feature from the target ID. |
| A code object compiled with a target ID specifying the default |
| value of a target feature can be loaded and executed on a processor |
| configured with the target feature on or off. |
| |
| *On* |
| Specified by ``+``, indicating the target feature is enabled. A code |
| object compiled with a target ID specifying a target feature on |
| can only be loaded on a processor configured with the target feature on. |
| |
| *Off* |
| specified by ``-``, indicating the target feature is disabled. A code |
| object compiled with a target ID specifying a target feature off |
| can only be loaded on a processor configured with the target feature off. |
| |
| .. _compatibility-target-id: |
| |
| Compatibility Rules for Target ID |
| --------------------------------- |
| |
| A code object compiled for a Target ID is considered compatible for a |
| target, if: |
| |
| * Their processor is same. |
| * Their feature set is compatible as defined above. |
| |
| There are two forms of target ID: |
| |
| *Non-Canonical Form* |
| The non-canonical form is used as the input to user commands to allow the user |
| greater convenience. It allows both the primary and alternative processor name |
| to be used and the target features may be specified in any order. |
| |
| *Canonical Form* |
| The canonical form is used for all generated output to allow greater |
| convenience for tools that consume the information. It is also used for |
| internal passing of information between tools. Only the primary and not |
| alternative processor name is used and the target features are specified in |
| alphabetic order. Command line tools convert non-canonical form to canonical |
| form. |
| |
| Target Specific information |
| =========================== |
| |
| Target specific information is available for the following: |
| |
| *AMD GPU* |
| AMD GPU supports target ID and target features. See `User Guide for AMDGPU Backend |
| <https://llvm.org/docs/AMDGPUUsage.html>`_ which defines the `processors |
| <https://llvm.org/docs/AMDGPUUsage.html#amdgpu-processors>`_ and `target |
| features <https://llvm.org/docs/AMDGPUUsage.html#amdgpu-target-features>`_ |
| supported. |
| |
| Most other targets do not support target IDs. |
| |
| Archive Unbundling |
| ================== |
| |
| Unbundling of a heterogeneous device archive (HDA) is done to create device specific |
| archives. HDA is in a format compatible with GNU ``ar`` utility and contains a |
| collection of bundled device binaries where each bundle file will contain |
| device binaries for a host and one or more targets. The output device-specific |
| archive is in a format compatible with GNU ``ar`` utility and contains a |
| collection of device binaries for a specific target. |
| |
| :: |
| |
| Heterogeneous Device Archive, HDA = {F1.X, F2.X, ..., FN.Y} |
| where, Fi = Bundle{Host-DeviceBinary, T1-DeviceBinary, T2-DeviceBinary, ..., |
| Tm-DeviceBinary}, |
| Ti = {Target i, qualified using Bundle Entry ID}, |
| X/Y = \*.bc for AMDGPU and \*.cubin for NVPTX |
| |
| Device Specific Archive, DSA(Tk) = {F1-Tk-DeviceBinary.X, F2-Tk-DeviceBinary.X, ... |
| FN-Tk-DeviceBinary.Y} |
| where, Fi-Tj-DeviceBinary.X represents device binary of i-th bundled device |
| binary file for target Tj. |
| |
| The clang-offload-bundler extracts compatible device binaries for a given target |
| from the bundled device binaries in a heterogeneous device archive and creates |
| a target-specific device archive without bundling. |
| |
| The clang-offload-bundler determines whether a device binary is compatible |
| with a target by comparing bundle IDs. Two bundle IDs are considered |
| compatible if: |
| |
| * Their offload kinds are the same |
| * Their target triples are the same |
| * Their Target IDs are the same |
| |
| Creating a Heterogeneous Device Archive |
| --------------------------------------- |
| |
| 1. Compile source file(s) to generate object file(s) |
| |
| :: |
| |
| clang -O2 -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa,amdgcn-amd-amdhsa,\ |
| nvptx64-nvidia-cuda, nvptx64-nvidia-cuda \ |
| -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906:sramecc-:xnack+ \ |
| -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906:sramecc+:xnack+ \ |
| -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_70 \ |
| -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_80 \ |
| -c func_1.c -o func_1.o |
| |
| clang -O2 -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa,amdgcn-amd-amdhsa, |
| nvptx64-nvidia-cuda, nvptx64-nvidia-cuda \ |
| -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906:sramecc-:xnack+ \ |
| -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906:sramecc+:xnack+ \ |
| -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_70 \ |
| -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_80 \ |
| -c func_2.c -o func_2.o |
| |
| 2. Create a heterogeneous device archive by combining all the object file(s) |
| |
| :: |
| |
| llvm-ar cr libFatArchive.a func_1.o func_2.o |
| |
| Extracting a Device Specific Archive |
| ------------------------------------ |
| |
| UnbundleArchive takes a heterogeneous device archive file (".a") as input |
| containing bundled device binary files, and a list of offload targets (not |
| host), and extracts the device binaries into a new archive file for each |
| offload target. Each resulting archive file contains all device binaries |
| compatible with that particular offload target. Compatibility between a |
| device binary in HDA and a target is based on the compatibility between their |
| bundle entry IDs as defined in :ref:`compatibility-bundle-entry-id`. |
| |
| Following cases may arise during compatibility testing: |
| |
| * A binary is compatible with one or more targets: Insert the binary into the |
| device-specific archive of each compatible target. |
| * A binary is not compatible with any target: Skip the binary. |
| * One or more binaries are compatible with a target: Insert all binaries into |
| the device-specific archive of the target. The insertion need not be ordered. |
| * No binary is compatible with a target: If ``allow-missing-bundles`` option is |
| present then create an empty archive for the target. Otherwise, produce an |
| error without creating an archive. |
| |
| The created archive file does not contain an index of the symbols and device |
| binary files are named as <<Parent Bundle Name>-<DeviceBinary's TargetID>>, |
| with ':' replaced with '_'. |
| |
| Usage |
| ----- |
| |
| :: |
| |
| clang-offload-bundler --unbundle --inputs=libFatArchive.a -type=a \ |
| -targets=openmp-amdgcn-amdhsa-gfx906:sramecc+:xnack+, \ |
| openmp-amdgcn-amdhsa-gfx908:sramecc-:xnack+ \ |
| -outputs=devicelib-gfx906.a,deviceLib-gfx908.a |
| |
| .. _additional-options-archive-unbundling: |
| |
| Additional Options while Archive Unbundling |
| ------------------------------------------- |
| |
| **-allow-missing-bundles** |
| Create an empty archive file if no compatible device binary is found. |
| |
| **-check-input-archive** |
| Check if input heterogeneous device archive follows rules for composition |
| as defined in :ref:`code-object-composition` before creating device-specific |
| archive(s). |
| |
| **-debug-only=CodeObjectCompatibility** |
| Verbose printing of matched/unmatched comparisons between bundle entry id of |
| a device binary from HDA and bundle entry ID of a given target processor |
| (see :ref:`compatibility-bundle-entry-id`). |
| |
| Compression and Decompression |
| ============================= |
| |
| ``clang-offload-bundler`` provides features to compress and decompress the full |
| bundle, leveraging inherent redundancies within the bundle entries. Use the |
| `-compress` command-line option to enable this compression capability. |
| |
| The compressed offload bundle begins with a header followed by the compressed binary data: |
| |
| - **Magic Number (4 bytes)**: |
| This is a unique identifier to distinguish compressed offload bundles. The value is the string 'CCOB' (Compressed Clang Offload Bundle). |
| |
| - **Version Number (16-bit unsigned int)**: |
| This denotes the version of the compressed offload bundle format. The current version is `2`. |
| |
| - **Compression Method (16-bit unsigned int)**: |
| This field indicates the compression method used. The value corresponds to either `zlib` or `zstd`, represented as a 16-bit unsigned integer cast from the LLVM compression enumeration. |
| |
| - **Total File Size (32-bit unsigned int)**: |
| This is the total size (in bytes) of the file, including the header. Available in version 2 and above. |
| |
| - **Uncompressed Binary Size (32-bit unsigned int)**: |
| This is the size (in bytes) of the binary data before it was compressed. |
| |
| - **Hash (64-bit unsigned int)**: |
| This is a 64-bit truncated MD5 hash of the uncompressed binary data. It serves for verification and caching purposes. |
| |
| - **Compressed Data**: |
| The actual compressed binary data follows the header. Its size can be inferred from the total size of the file minus the header size. |
