Re: Building "Fat" Mac Binary, or Cross-Compiling from ARM arch to x86-64

On 1/2/2025 10:59 PM, Viktor Dukhovni wrote:
> Unfortunately, that can't trivially work for OpenSSL, because
> architecture-specific assembly targets are included in the build.  You'd
> need to build *both* the ARM *and* X86_64 assembly targets, invoking the
> appropriate assembler on each one, and producing either object code for
> that particular platform for inclusion in the "fat" binary, or somehow
> producting a "fat" objec that is "empty" for one of the targets.
>
> How to do that, requires more detailed knowledge of fat binaries than I
> can muster.

To create a fat binary on macOS, you need to use lipo command to combine 
both x64 and arm64 libraries that must be built separately as Viktor 
explained:
lipo -create -output libcrypto.dylib libcrypto.dylib.x64 
libcrypto.dylib.arm64

We have a script that automates this process. It fetches the OpenSSL 
tarball from GitHub, performs separate x64 and arm64 builds, invokes 
lipo, updates the install_name and handles code signing. The script is 
too long to include here so I’ve shared it as a GitHub gist:

https://gist.github.com/idrassi/cf4ef1a81f9bb5b7d7b3e8382b942665

Take a look at the function lipo_dylib that calls lipo:

-----------------------------------------------------------------

lipo_dylib() {
     local lib_name="\$1"
     local src_x86_64="${INSTALL_PREFIX_X86_64}/lib/${lib_name}"
     local src_arm64="${INSTALL_PREFIX_ARM64}/lib/${lib_name}"
     local dest="${INSTALL_PREFIX_UNIVERSAL}/lib/${lib_name}"

     if [[ -f "${src_x86_64}" && -f "${src_arm64}" ]]; then
         echo "Creating universal binary for ${lib_name}..."
         lipo -create -output "${dest}" "${src_x86_64}" "${src_arm64}"

         # Use install_name_tool to set the correct install_name
         echo "Updating install_name for ${lib_name}..."
         install_name_tool -id "${INSTALL_PATH}/lib/${lib_name}" 
"${dest}" || {
             echo "Failed to update install_name for ${lib_name}"
             exit 1
         }

         # If libssl depends on libcrypto, update the dependency path
         if [[ "${lib_name}" == "libssl.3.dylib" ]]; then
             echo "Updating dependency of libssl.3.dylib to point to 
${INSTALL_PATH}/lib/libcrypto.3.dylib..."
             install_name_tool -change 
"/tmp/openssl_x86_64/lib/libcrypto.3.dylib" 
"${INSTALL_PATH}/lib/libcrypto.3.dylib" "${dest}" || {
                 echo "Failed to update libssl.3.dylib dependency for 
x86_64"
                 exit 1
             }
             install_name_tool -change 
"/tmp/openssl_arm64/lib/libcrypto.3.dylib" 
"${INSTALL_PATH}/lib/libcrypto.3.dylib" "${dest}" || {
                 echo "Failed to update libssl.3.dylib dependency for 
arm64"
                 exit 1
             }
         fi
     else
         echo "Error: Missing ${lib_name} for one or both architectures."
         exit 1
     fi
}
--------------------

Mounir IDRASSI

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