The purpose of the producers section is to provide an optional, highly-structured record of all the distinct tools that were used to produce a given WebAssembly module. A primary purpose of this record is to allow broad analysis of toolchain usage in the wild, which can help inform both wasm producers and consumers.
The producers section is a custom section and thus has no semantic effects and can be stripped at any time. Since the producers section is relatively small, tools are encouraged to emit the section or include themselves in an existing section by default, keeping the producers section even in release builds.
WebAssembly consumers should avoid using the producers section to derive optimization hints. To ensure portable performance, hints should be standardized in a separate custom section, probably in the core spec's Custom Sections appendix.
An additional goal of the producers section is to provide a discrete, but easily-growable list of known tools/languages for each record field. This avoids the skew that otherwise happens with unstructured strings. Unknown names do not invalidate an otherwise-valid producers section. However, wasm consumers may provide less accurate telemetry results for unknown names or even emit diagnostics encouraging the name to be put on the known list.
Since version information is useful, but highly-variable, each field value is accompanied with a version string so that the name can remain stable over time without requiring frequent updates to the known list.
Custom section name field: producers
The producers section may appear only once, and only after the Name section.
The producers section contains a sequence of fields with unique names, where the end of the last field must coincide with the last byte of the producers section:
| Field | Type | Description |
|---|---|---|
| field_count | varuint32 |
number of fields that follow |
| fields | field* |
sequence of field_count field records |
where a field is encoded as:
| Field | Type | Description |
|---|---|---|
| field_name | name | name of this field |
| field_value_count | varuint32 |
number of value strings that follow |
| field_values | versioned-name* |
sequence of field_value_count name-value pairs |
where a versioned-name is encoded as:
| Field | Type | Description |
|---|---|---|
| name | name | name of the language/tool |
| version | name | version of the language/tool |
with the additional constraint that each field_name in the list must be unique and found in the first column of the following table, and each of a given field_name's field_values's name strings must be unique and found in the second column of the field_name's row.
| field_name | field_value name strings |
|---|---|
language |
source language list |
processed-by |
individual tool list |
sdk |
SDK list |
The following lists contain all the known names for the fields listed above. If your tool is not on this list and you'd like it to be, please submit a PR.
It is possible for multiple source languages to be present in a single module when the output of multiple compiled languages are statically linked together.
watCC++Rust
It is possible (and common) for multiple tools to be used in the overall pipeline that produces and optimizes a given wasm module.
wabtLLVMclanglldBinaryenrustcwasm-bindgenwasm-packwebassemblyjswasm-snip
While an SDK is technically just another tool, the sdk field designates the
top-level "thing" that the developer installs and interacts with directly to
produce the wasm module.
EmscriptenWebpack
TODO