mgo

Build your code for multiple GOAMD64 variants and bundle all of them in a launcher capable of picking at runtime the most appropriate variant for the processor in use.

This is mostly useful if you want to provide GOAMD64 variants because of the extra runtime performance this yields, but you have no control over which processor microarchitecture the executable will be run on.

Install

go install github.com/CAFxX/mgo@latest

Usage

When building your code just replace go build [...] with mgo [...]: the resulting executable will contain 4 variants, each optimized for one of GOAMD64=v1, GOAMD64=v2, GOAMD64=v3 and GOAMD64=v4, and a launcher that will pick the appropriate one at runtime.

At runtime it is possible to override which variant is used by specifying in the GOAMD64 environment variable one of the values v1, v2, v3, or v4.

To check which version is being executed you can add the MGODEBUG=log environment variable when starting the compiled binary. In this case the launcher will print on stderr a line similar to the following at startup (in this example, to signal that the v3 variant is being used):

[mgo] launcher: starting variant GOAMD64=v3

Otherwise you can find out which version is being used by resolving the /proc/<PID>/exe symlink, where <PID> is the process ID of the launched process:

$ PID=...
$ readlink /proc/$PID/exe
/memfd:/usr/bin/foobar [GOAMD64=v3] (deleted)

You can extract a specific embedded executable using MGODEBUG=extract when starting the compiled binary, e.g. MGODEBUG=extract GOAMD64=v3 will dump to stdout the executable for GOAMD64=v3 instead of starting it.

Notes

• mgo requires Go >= 1.20
• The resulting executable will be over 4 times as large as a normal build output
• Startup of the resulting executable is going to be a bit slower (tens of milliseconds)
• Currently only GOOS=linux and GOARCH=amd64 are supported, and only in buildmodes that produce executables (not archives, plugins, or libraries)

TODO

• Further minimize launcher overhead
  • Start process with GOMAXPROCS=1 and GOGC=off instead of setting them in init
  • Avoid the write to the memfd (find ways to populate the new process directly from the binary in RODATA)
• Embed build metadata of the built v1 variant into the launcher, so that introspection tools can use it
• Support GOARCH=arm and GOARCH=arm64

Quick sanity check

rm -f mgo* && \
echo stage0 && go build && \
echo stage1 && ./mgo -o mgo1 && sha1sum mgo1 && \
echo stage2 && ./mgo1 -o mgo2 && sha1sum mgo2 && \
echo stage3 && ./mgo2 -o mgo3 && sha1sum mgo3

This command should succeed and produce three identical hashes.