Architecture-Specific Build Settings in Xcode 13

Question

Created Feb ’22

Replies 1

Boosts 0

Views 2k

Participants 2

I'm trying to use architecture-specific build settings in my Xcode Framework so that I can handle the case of the Apple Silicon Mac and the Intel Mac separately. I need to use this build setting as a macro in Metal to check whether the half data type is supported on the CPU (it's supported on Apple Silicon but not supported on Intel).

My current implementation uses an xcconfig file with the following line:

IS_X86_64[arch=x86_64] = 1

Then, in my build settings I have the following user-defined condition (from the xcconfig):

Screen Shot 2022-02-05 at 11.10.53 AM.png

I then create the macro IS_INTEL so it can be used in Metal:

Screen Shot 2022-02-05 at 11.11.16 AM.png

Here's The Problem

In theory I feel like this should work. However, running my Metal app on my Intel mac yields 0 for IS_X86_64. The first thing I did was check whether I set up my build setting correctly and replaced

IS_X86_64[arch=x86_64] = 1 with IS_X86_64[arch=*] = 1

This worked so I knew that the problem had to be that my current architecture wasn't being represented correctly. Diving further into why this was happening, it turns out that the value for CURRENT_ARCH (which should hold the value for the current device architecture that the project is being run on) is undefined_arch.

In their Xcode 10 release notes, apple mentioned something about undefined_arch saying:

The new build system passes undefined_arch as the value for the ARCH environment variable when running shell script build phases. The value was previously not well defined. Any shell scripts depending on this value must behave correctly for all defined architectures being built, available via the ARCHS environment variable.

However, I'm not building my project on the shell and I don't have any shell scripts. Does anyone know how I can fix this so that architecture-specific build settings behave as they should?

Boost

Answer 1

Graphics and Games Engineer OP

Apple

Feb ’22

For Metal code, you can use _Float16 (an ISO C language extension) which is architecture independent and works both on x86_64 and arm64 CPU-side.

Other types like half2 can be used like the following:

using half   = _Float16;
using half2  = __attribute__((__ext_vector_type__(2))) half;
using half3  = __attribute__((__ext_vector_type__(3))) half;
using half4  = __attribute__((__ext_vector_type__(4))) half;

Outside of this context, please see "Wrap Platform-Specific Code with Conditional Compilation Macros" in Building a Universal Binary for conditional macros you can use to distinguish between different architectures at compile time.

0