How to Generate A Fat Binary For Mac

So at work, we needed to ship a binary for Mac. With Go, it is super easy to build a binary for any OS and Architecture. However, having separate binaries would mean additional logic to detect the target and then deliver them. Wouldn’t it be nice to ship just one binary which work on all Macs (Intel and Apple Silicon based) We call this a Fat Binary.

Here is how you can do it:

Consider this short Go program:

Save this as main.go

package main import "fmt" func main() { fmt.Println("Fat Binary") }

Now, you can build a binary for both the architecture like this:

GOOS=darwin GOARCH=arm64 go build -o mac_arm64 main.go GOOS=darwin GOARCH=amd64 go build -o mac_amd64 main.go

When you run this, you will see two binaries your folder:

ls -rwxr-xr-x@ 1 vinitkumar staff 2.1M Dec 18 18:00 mac_amd64 -rwxr-xr-x@ 1 vinitkumar staff 2.1M Dec 18 18:00 mac_arm64

Alright, this looks decent, now how do we stitch them together to make a big fat binary that works on all Macs?

Enter Lipo. This utility can take two binaries and then spit out a far binary that works on all CPU architectures. On Mac, with command line tools installed it just available as lipo

So doing which lipo gives /usr/bin/lipo. On Ubuntu however, it comes bundles with llvm. So you need to do this:

sudo apt install llvm # and then it is present as `llvm-lipo-14` depending on which llvm it is, for me it is llvm-14 So `/usr/bin/llvm-lipo-14'

Now, as we have located Lipo, now, we will use it to generate the fat binary.

# on Ubuntu llvm-lipo-14 -create -output "mac_universal" "mac_arm64" "mac_amd64" # on Mac lipo -create -output "mac_universal" "main_arm64" "main_amd64"

Once created, we can verify if the binary is proper using the file util.

file mac_universal mac_universal: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64] mac_universal (for architecture x86_64): Mach-O 64-bit executable x86_64 mac_universal (for architecture arm64): Mach-O 64-bit executable arm64

You can execute this on either of the CPUs and it would just work.

Bonus code

Here is code to generate the Ascii diagram above. You need to have Pillow installed though.

from PIL import Image, ImageDraw, ImageFont import os # Create a new image with white background width = 800 height = 600 image = Image.new('RGB', (width, height), 'white') draw = ImageDraw.Draw(image) # Try to load a font (you may need to adjust the path) try: font = ImageFont.truetype("Arial.ttf", 32) except: font = ImageFont.load_default() # Draw the outer rectangle draw.rectangle([(50, 50), (width-50, height-50)], outline='black', width=2) # Draw the vertical divider draw.line([(width/2, 100), (width/2, 400)], fill='black', width=2) # Draw the horizontal dividers draw.line([(50, 250), (width-50, 250)], fill='black', width=2) draw.line([(50, 400), (width-50, 400)], fill='black', width=2) # Add text draw.text((width/4, 150), "x86_64\nCode", font=font, fill='black', anchor="mm") draw.text((3*width/4, 150), "ARM64\nCode", font=font, fill='black', anchor="mm") draw.text((width/4, 325), "x86_64\nResources", font=font, fill='black', anchor="mm") draw.text((3*width/4, 325), "ARM64\nResources", font=font, fill='black', anchor="mm") draw.text((width/2, 450), "Shared Resources", font=font, fill='black', anchor="mm") draw.text((width/2, 75), "Fat Binary", font=font, fill='black', anchor="mm") # Save the image image.save('fat_binary_diagram.png')