Fat binaries & slices

A Mach-O fat (universal) binary packs multiple architecture slices into one file. To symbolize, atosl needs to know which slice you mean.

Build a fat binary (macOS)

clang -g -O1 -arch arm64  -c sample.c -o sample.arm64.o
clang -g -arch arm64  sample.arm64.o  -o sample.arm64
clang -g -O1 -arch x86_64 -c sample.c -o sample.x86.o
clang -g -arch x86_64 sample.x86.o    -o sample.x86

lipo -create sample.arm64 sample.x86 -output fat
lipo -info fat
# Architectures in the fat file: fat are: x86_64 arm64

What happens without a selector

If the binary has more than one slice and you do not choose one, atosl refuses to guess and lists what is available:

atosl -o fat -l 0x100000000 0x100000460

fat Mach-O contains multiple slices.
Use -a/--arch or --uuid to select one.
Available slices:
- arch=x86_64 uuid=80D7C53A-F639-3261-9DC0-4AB2DAF6D0BD
- arch=arm64 uuid=74B3ADB4-0508-3A1E-8B6A-8FC92DACCE66

Select by architecture

atosl -o fat -l 0x100000000 --arch arm64  0x100000460
atosl -o fat -l 0x100000000 --arch x86_64 0x100000470

Common aliases are accepted: arm64/aarch64, x86_64/amd64, i386/x86.

Select by UUID

When you have the UUID from a crash report, select the slice directly. Hyphens are optional:

atosl -o fat -l 0x100000000 --uuid 74B3ADB4-0508-3A1E-8B6A-8FC92DACCE66 0x100000460
atosl -o fat -l 0x100000000 --uuid 80D7C53AF63932619DC04AB2DAF6D0BD       0x100000470

--arch / --uuid also pick from a directory

The same --uuid that selects a slice inside a fat binary also selects a file when -o is a directory. See Input sources.

Tip: each slice has its own addresses

The same source compiled for two architectures lands at different addresses and can even map to slightly different source lines after optimization. Always pair an address with the slice it came from.