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[clang-offload-bundler] Add support for -check-input-archive (llvm#73709
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In this patch, we add support for checking a heterogeneous archive. We
also significantly improve the clang-offload-bundler documentation.
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@lamb-j
lamb-j authored Nov 30, 2023
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312 changes: 254 additions & 58 deletions clang/docs/ClangOffloadBundler.rst
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Expand Up @@ -30,58 +30,139 @@ 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
======================
Several text and binary file formats are supported for bundling/unbundling. See
:ref:`supported-file-formats-table` for a list of currently supported 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 Extension | 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 objects | a | Binary |
+--------------------+----------------+-------------+
| Precompiled header | gch | Binary |
+--------------------+----------------+-------------+
| Clang AST file | ast | Binary |
+--------------------+----------------+-------------+
+--------------------------+----------------+-------------+
| 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 format of the bundled files is currently very simple: text formats are
concatenated with comments that have a magic string and bundle entry ID in
between.
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:

::

"Comment OFFLOAD_BUNDLER_MAGIC_STR__START__ 1st Bundle Entry ID"
Bundle 1
"Comment OFFLOAD_BUNDLER_MAGIC_STR__END__ 1st Bundle Entry ID"
...
"Comment OFFLOAD_BUNDLER_MAGIC_STR__START__ Nth Bundle Entry ID"
Bundle N
"Comment OFFLOAD_BUNDLER_MAGIC_STR__END__ 1st Bundle Entry ID"
<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:

Expand Down Expand Up @@ -126,8 +207,8 @@ The layout of a bundled code object is defined by the following table:
Bundle Entry ID
===============

Each entry in a bundled code object (see
:ref:`clang-bundled-code-object-layout`) has a bundle entry ID that indicates
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:
Expand Down Expand Up @@ -193,11 +274,30 @@ Where:
The canonical target ID of the code object. Present only if the target
supports a target ID. See :ref:`clang-target-id`.

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.
.. _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:

Expand Down Expand Up @@ -247,6 +347,17 @@ Where:
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*
Expand Down Expand Up @@ -279,14 +390,14 @@ Most other targets do not support target IDs.
Archive Unbundling
==================

Unbundling of heterogeneous device archive is done to create device specific
archives. Heterogeneous Device Archive 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.
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.

.. code::
::

Heterogeneous Device Archive, HDA = {F1.X, F2.X, ..., FN.Y}
where, Fi = Bundle{Host-DeviceBinary, T1-DeviceBinary, T2-DeviceBinary, ...,
Expand All @@ -299,16 +410,101 @@ and contains a collection of device binaries for a specific target.
where, Fi-Tj-DeviceBinary.X represents device binary of i-th bundled device
binary file for target Tj.

clang-offload-bundler extracts compatible device binaries for a given target
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.
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).

clang-offload-bundler determines whether a device binary is compatible with a
target by comparing bundle ID's. Two bundle ID's are considered compatible if:

* Their offload kind are the same
* Their target triple are the same
* Their GPUArch are the same
**-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
=============================
Expand Down
2 changes: 1 addition & 1 deletion clang/include/clang/Driver/OffloadBundler.h
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Expand Up @@ -66,7 +66,7 @@ class OffloadBundler {
llvm::Error UnbundleArchive();
};

/// Obtain the offload kind, real machine triple, and an optional GPUArch
/// Obtain the offload kind, real machine triple, and an optional TargetID
/// out of the target information specified by the user.
/// Bundle Entry ID (or, Offload Target String) has following components:
/// * Offload Kind - Host, OpenMP, or HIP
Expand Down
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