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Gnopher Hole

Native bindings

Gno has support for "natively-defined" functions exclusively within the standard libraries. These are functions which are declared in Gno code, but only defined in Go. There are generally three reasons why a function should be natively defined:

  1. It relies on inspecting the Gno Virtual Machine itself, i.e. std.AssertOriginCall or std.CurrentRealm.
  2. It relies on unsafe, or other features which are not planned to be available in the GnoVM, i.e. math.Float64frombits.
  3. Its native Go performance significantly outperforms the Gno counterpart by several orders of magnitude, and it is used in crucial code or hot paths in many programs, i.e. sha256.Sum256.

Native bindings are made to be a special feature which can be help overcome pure Gno limitations, but it is not a substitute for writing standard libraries in Gno.

There are three components to a natively bound function in Gno:

  1. The Gno function declaration, which must be a top-level function with no body (and no brackets), i.e. crypto/sha256/sha256.gno.
  2. The Go function definition, which must be a top-level function with the same name and signature, i.e. crypto/sha256/sha256.go.
  3. When the two above are present and valid, the native binding can be created by executing the code generator: either by executing go generate from the stdlibs directory, or run make generate from the gnovm directory. This generates the native.go file available in the stdlibs directory, which provides the binding itself to then be used by the GnoVM.

The code generator in question is available in the misc/genstd directory. There are some quirks and features that must be kept in mind when writing native bindings, which are the following:

  • Unexported functions (i.e. func sum256(b []byte)) must have their Go counterpart prefixed with X_ in order to make the functions exported (i.e. func X_sum256(b []byte)).
  • The Go function declaration may specify as the first argument m *gno.Machine, where gno is an import for This gives the function access to the Virtual Machine state, and is used by functions like std.AssertOriginCall().
  • The Go function may change the type of any parameter or result to gno.TypedValue, where gno is an import for the above import path. This means that the native.go generated code will not attempt to automatically convert the Gno value into the Go value, and can be useful for unsupported conversions like interface values.
  • A small set of named types are "linked" between their Gno version and Go counterpart. For instance, std.Address in Gno is (".../tm2/pkg/crypto").Bech32Address in Go. A list of these can be found in misc/genstd/mapping.go.
  • Not all type literals are currently supported when converting from their Gno version to their Go counterpart, i.e. struct and map literals. If you intend to use these, modify the code generator to support them.
  • The code generator does not inspect any imported packages from the Go native code to determine the default package identifier (i.e. the package clause). For example, if a package is in foo/bar, but declares package xyz, when importing foo/bar the generator will assume the name to be bar instead of xyz. You can add an identifier to the import to fix this and use the identifier you want/need, such as import gno "".

Adding new standard libraries

New standard libraries may be added by simply creating a new directory (whose path relative to the stdlibs directory will be the import path used in Gno programs). Following that, the suggested approach for adding a Go standard library is to copy the original files from the Go source tree, and renaming their extensions from .go to .gno.


As a small aid, this bash one-liner can be useful to convert all the file extensions:

for i in *.go; do mv $i "$(echo $i | sed 's/\.go$/.gno/')"; done

Following that, the suggested approach is to iteratively try running gno test ., while fixing any errors that may come out of trying to test the package.

Some things to keep in mind:

  • Gno doesn't support assembly functions and build tags. Some Go packages may contain assembly versions for different architecture and a generic.go file containing the architecture-independent version. The general approach is that of removing everything architecture/os-specific except for the generic.go file.
  • Gno doesn't support reflection at the time of writing, which means that for now many packages which rely heavily on reflection have to be delayed or reduced while we figure out the details on how to implement reflection. Aside from the reflect package itself, this also translates to very common packages still not available in Gno, such as fmt or encoding/json.
  • In the package documentation, specify the Go version from which the library was taken.
  • All changes from the Go standard libraries must be explicitly marked, possibly with // XXX comments as needed.

If you intend to create a PR to add a new standard library, remember to update Go<>Gno compatibility accordingly.