gorebuild command

Gorebuild rebuilds and verifies the distribution files posted at https://go.dev/dl/.

Usage:

gorebuild [-p N] [goos-goarch][@version]...

With no arguments, gorebuild rebuilds and verifies the files for all systems (that is, all operating system-architecture pairs) for up to three versions of Go:

• the most recent patch release of the latest Go major version,
• the most recent patch release of the previous Go major version, and
• the latest release candidate of an upcoming Go major version, if there is one.

Only Go versions starting at Go 1.21 or later are considered for this default set of versions, because Go 1.20 and earlier did not ship reproducible toolchains.

With arguments, gorebuild rebuilds the files only for the named toolchains:

• The syntax goos-goarch (for example, "linux-amd64") denotes the files for that specific system's toolchains for the three default versions.
• The syntax @version (for example, "@go1.21rc3") denotes the files for all systems, at a specific Go version.
• The syntax goos-goarch@version (for example, "linux-amd64@go1.21rc3") denotes the files for a specific system at a specific Go version.

The -p flag specifies how many toolchain rebuilds to run in parallel (default 2).

When running on linux-amd64, gorebuild does a full bootstrap, building Go 1.4 (written in C) with the host C compiler, then building Go 1.17 with Go 1.4, then building Go 1.20 using Go 1.17, and so on, up to the target toolchain. On other systems, gorebuild downloads a binary distribution of the bootstrap toolchain it needs. For example, Go 1.21 required Go 1.17, so to rebuild and verify Go 1.21, gorebuild downloads and uses the latest binary distribution of the Go 1.17 toolchain (specifically, Go 1.17.13) from https://go.dev/dl/.

In general, gorebuild checks that the local rebuild produces a bit-for-bit identical copy of the file posted at https://go.dev/dl/. Similarly, gorebuild checks that the local rebuild produces a bit-for-bit identical copy of the module form of the toolchain used by Go 1.21's toolchain downloads (also served by https://go.dev/dl/).

However, in a few cases gorebuild does not insist on a bit-for-bit comparison. These cases are:

• For macOS, https://go.dev/dl/ posts .tar.gz files containing binaries signed by Google's code-signing key. Gorebuild has no way to sign the binaries it produces using that same key. Instead, gorebuild compares the content of the rebuilt archive with the content of the posted archive, checking that non-executables match exactly and that executables match exactly after stripping their code signatures. The same comparison is applied to the module form of the toolchain.

• For macOS, https://go.dev/dl/ posts a .pkg installer file. Gorebuild does not run the macOS tools to rebuild that installer. Instead, it parses the .pkg file and checks that the contents match the rebuilt .tar.gz file exactly, again after stripping code signatures. The .pkg is permitted to have one extra file, /etc/paths.d/go, which is unique to the .pkg form.

• For Windows, https://go.dev/dl/ posts a .msi installer file. Gorebuild does not run the Windows tools to rebuild that installer. Instead, it invokes the Unix program “msiextract” to unpack the file and then checks that the contents match the rebuilt .zip file exactly. If “msiextract” is not found in the PATH, the .msi file is skipped rather than considered a failure.

Gorebuild prints log messages to standard error but also accumulates them in a structured report. Before exiting, it writes the report as JSON to gorebuild.json and as HTML to gorebuild.html.

Gorebuild exits with status 0 when it succeeds in writing a report, whether or not the report verified all the posted files.