Support for iOS cross compiling using cmake 3.14+

[kylefleming]

As of version 3.14, cmake has added support for cross compiling iOS (see https://cmake.org/cmake/help/latest/release/3.14.html?highlight=cross#platforms).

This means that -miphone-version-min style parameters get added automatically. This also means that currently when using cmake-rs, these parameters are being added twice, and often with conflicting values.

I've found that in order the support the new system, the following CMAKE variables need to be set:

• CMAKE_SYSTEM_NAME (Set to iOS)
• CMAKE_OSX_ARCHITECTURES (Set to one of: arm64, armv7, armv7s, i386, or x86_64)
• CMAKE_OSX_DEPLOYMENT_TARGET (Could likely be pulled from the IPHONEOS_DEPLOYMENT_TARGET env variable)
• CMAKE_OSX_SYSROOT (Set to either: iphoneos or iphonesimulator)

The target triplets for iOS are:

• aarch64-apple-ios
• armv7-apple-ios
• armv7s-apple-ios
• i386-apple-ios
• x86_64-apple-ios

Additionally, I found that cmake-rs (via cc-rs) is setting the following compiler flags which are not added by cmake:

• -fPIC
• -fembed-bitcode

Note: cmake 3.14 also added support for tvOS and watchOS, but since I don't support them in my own app, I don't know what's required to support them.

[alexcrichton]

Seems reasonable to me to support! I don't do much ios development myself but I'm more than willing to review PRs!

[davemilter]

Did #93 fix this issue? I try this "hello world" project:
https://github.com/davemilter/cmake_rs_hello_world

it builds without modification for Android, but for iOS:

-- Check for working C compiler: /usr/bin/cc - broken
clang: warning: using sysroot for 'MacOSX' but targeting 'iPhone' [-Wincompatible-sysroot]
 ld: warning: -headerpad_max_install_names is ignored when used with -bitcode_bundle (Xcode setting ENABLE_BITCODE=YES)
ld: dynamic main executables must link with libSystem.dylib for architecture arm64

On this system cmake crosscomping for iOS works, if I manually invoke cmake,
but always pass properly crafted cmake toolchain file to cmake.

Should this work without toolchain file, or I have to pass it?
cc @simlay

[davemilter]

Or, it is actually works. The problem in that crate on crates.io has no #93 . @alexcrichton, any plans for new release with iOS support fix?

[alexcrichton]

Oops sorry about that, published now!

[kylefleming]

@alexcrichton Could you reopen this issue on account of the fix having been reverted, as described in #96?

[alexcrichton]

Sure!

[daxpedda]

I have encountered this issue while cross-compiling between Intel and Apple Silicon MacOS, I fixed it by simply applying CMAKE_OSX_ARCHITECTURES.