Document how to reproduce our binaries

[bradfitz]

(Forking off @Foxboron's request at #81 (comment) for instructions on how to reproduce our official Linux binaries)

• we set the tailscale_go build tag
• we use the https://github.com/tailscale/go repo built from its CI: https://github.com/tailscale/go/releases (the exact version of Go is printed when tailscaled starts)
• the version file that's auto-generated by our redo-based build system is:

$ cat ver.go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// +build redo

package version

const LONG = "1.1.425-g3f107922c"
const SHORT = "1.1.425"

• Go is run like:

redo  out/x86_64-linux/oss/cmd/tailscale/tailscale (resumed)
#!/bin/sh -e
# Per-platform settings for the go compiler.
# Auto-generated by go.od. Do not edit!
S='/home/bradfitz/src/tailscale.io'
export GO='/home/bradfitz/.cache/tailscale-go/bin/go'
export CC='cc'
export CFLAGS=''
export GO_LDFLAGS='-extldflags ""'
export GOOS=''
export GOARCH=''
export GOARM=''
export CGO_ENABLED='0'

# Necessary because CI forces GOROOT and we need
# to override it back.
export GOROOT=
redo    (../../../../../oss/version/all)                                                                                                                                            
redo    (../../../../../oss/version/version.h)
redo    oss/version/describe.txt
redo    oss/version/describe.txt (done)                                                                                                                                             

redo  out/x86_64-linux/oss/cmd/tailscale/tailscale (done)                                                                                                                           

....

        '$GO' build \\
            -v -trimpath -tags=redo,tailscale_go \\
            -ldflags "\$GO_LDFLAGS" \\
            -o "\$t" \\
            "\$pkg"

To close this issue we should:

1. make sure this is reproducible
2. document it somewhere

[danderson]

Trying to reproduce our binaries now, and yeah, this is hard/impossible right now because of weirdnesses in our build system. Making this a tracking bug for the things I find.

[danderson]

build_dist.sh should probably set CGO_ENABLED=0, to match our corp build system. This is a major source of diffoscope noise, since build_dist.sh ends up building a dynamically linked binary otherwise.

[danderson]

CGO_ENABLED=0 ./build_dist.sh -trimpath -o ../tailscale_cli tailscale.com/cmd/tailscale is where I'm at right now. Diffoscope still shows mass diffs, seemingly caused by our go.mod replace clauses in the corp repo, which change the package's recorded name in the binaries even though the submodule is at the same revision as the OSS-only build. The different names also causes file offsets to get bumped, causing mass diffs everywhere else.

[DentonGentry]

As of Tailscale 1.42, ./cmd/dist is used to build most platforms.