Mergeable libraries

mergeable_libraries.sh

# Section 1
# Create a class
echo "class MyClass {}" > file.swift
# Compile a static library
swiftc file.swift -static -emit-library -o libStaticExample.a
# Compile a dynamic library
swiftc file.swift -emit-library -o libDynamicExample.dylib
# Compile a mergeable library
swiftc file.swift -emit-library -Xlinker -make_mergeable -o libMergeableExample.dylib

# Section 2
# Outputs Mach-O header from static library
otool -h libStaticExample.a
# Mach header
#      magic  cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
# 0xfeedfacf 16777223          3  0x00           1    10       1520 0x00002000

# Outputs Mach-O header from dynamic library
otool -h libDynamicExample.dylib
# Mach header
#      magic  cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
# 0xfeedfacf 16777223          3  0x00           6    17       1952 0x00100085

# Outputs Mach-O header from mergeable library
otool -h libDynamicExample.dylib
# Mach header
#      magic  cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
# 0xfeedfacf 16777223          3  0x00           6    18       1976 0x00100085

# Section 3
# Diff from load commands between dynamic and mergeable library
diff <(otool -l libDynamicExample.dylib) <(otool -l libMergeableExample.dylib)
# > Load command 17
# >       cmd LC_ATOM_INFO
# >   cmdsize 16
# >   dataoff 49672
# >  datasize 8048