Fix cross-compilation on macOS with SDK and ARCH (#849)

* Fix cross-compilation on macOS with SDK and ARCH

Surprisingly, it's possible to cross-compile Themis Core for different
SDKs and architectures using our Makefile. For example,

    make SDK=macosx11.0 ARCH=arm64

will compile for Apple Silicon, provided that your Xcode toolchain is
actually capable of building that architecture.

You also need to have OpenSSL binaries with desired architecture
installed (for which you might need to tweak ENGINE_INCLUDE_PATH and
ENGINE_LIB_PATH separately). Or build ENGINE=boringssl to use embedded
BoringSSL that we can cross-compile too.

However, cross-compilation does not work because the architecture and
system library directories are not set at link time, so libthemis.dylib
it attempted to be linked for the native target which does not work.

Pass proper settings to LDFLAGS at configuration time so that
cross-compilation has a chance to work.

* Pass cross-compilation options to embedded BoringSSL build

If we seem to be cross-compiling, tell CMake what SDK it should use and
what architecture it should be building. It knows what to do next.

* Test cross-compilation on GitHub Actions

Throw in a job to make sure that cross-compilations stays in working
order. Unfortunately, we can't actually run unit tests, but hey, at
least it compiles.

.github/workflows/test-core.yaml

@@ -405,3 +405,31 @@ jobs:
           echo "Secure Session: socket interface"
           cc -o session_test client.c server.c session_test.c -lthemis -pthread
           ./session_test
+
+  macos-cross-compile:
+    name: macOS cross toolchain
+    runs-on: macos-10.15
+    steps:
+      - name: Install system dependencies
+        run: |
+          brew install cmake ninja
+      - name: Check out code
+        uses: actions/checkout@v2
+        with:
+          submodules: true
+      # We can't test OpenSSL builds since this requires OpenSSL libraries
+      # built for the target architecture (and Homebrew doesn't have any).
+      #
+      # GitHub's virtual environemnts can change the default version of Xcode
+      # and that changes the available SDKs. Check the combinations here:
+      # https://github.com/actions/virtual-environments/blob/main/images/macos/macos-10.15-Readme.md#xcode
+      - name: Build Themis Core (BoringSSL, arm64)
+        run: make SDK=macosx11.1 ARCH=arm64 ENGINE=boringssl
+      # Of course we can't run unit tests either because there is no emulator.
+      # So I will be satisifed to see the build succeed and produce binaries
+      # with expected architecture.
+      - name: Check binary architecture
+        run: |
+          set -x
+          test $(lipo -archs build/libsoter.0.dylib) = arm64
+          test $(lipo -archs build/libthemis.0.dylib) = arm64

CHANGELOG.md

@@ -66,6 +66,7 @@ _Code:_
     </details>
 
   - Fixed multiple buffer overflows in Secure Message ([#763](https://github.com/cossacklabs/themis/pull/763)).
+  - Fixed cross-compilation on macOS by setting `ARCH` and `SDK` variables ([#849](https://github.com/cossacklabs/themis/pull/849)).
 
 - **Android**
 
@@ -169,6 +170,8 @@ _Infrastructure:_
 - Added automated tests for Android example project ([#813](https://github.com/cossacklabs/themis/pull/813)).
 - Added automated tests for desktop Java example project ([#816](https://github.com/cossacklabs/themis/pull/816)).
 - Embedded BoringSSL now builds faster if Ninja is available ([#837](https://github.com/cossacklabs/themis/pull/837)).
+- Embedded BoringSSL can now be cross-compiled on macOS by setting `ARCH` and `SDK` variables ([#849](https://github.com/cossacklabs/themis/pull/849)).
+
 
 ## [0.13.10](https://github.com/cossacklabs/themis/releases/tag/0.13.10), May 26th 2021
 

configure

@@ -220,11 +220,13 @@ configure_macos_toolchain() {
         set_variable FRAMEWORKS   "$SDK_BASE/System/Library/Frameworks/"
         set_variable SDK_INCLUDES "$SDK_BASE/usr/include"
         append_variable CFLAGS "-isysroot \"$SDK_BASE\""
+        append_variable LDFLAGS "-isysroot \"$SDK_BASE\""
     fi
 
     if [ -n "${ARCH:-}" ]
     then
         append_variable CFLAGS "-arch $ARCH"
+        append_variable LDFLAGS "-arch $ARCH"
     fi
 }
 

src/soter/boringssl/soter.mk

@@ -40,6 +40,16 @@ ifneq ($(NINJA),)
 SOTER_ENGINE_CMAKE_FLAGS += -G Ninja
 endif
 
+# Cross-compilation support for macOS
+ifdef IS_MACOS
+ifdef SDK
+SOTER_ENGINE_CMAKE_FLAGS += -DCMAKE_OSX_SYSROOT=$(SDK)
+endif
+ifdef ARCH
+SOTER_ENGINE_CMAKE_FLAGS += -DCMAKE_OSX_ARCHITECTURES=$(ARCH)
+endif
+endif
+
 ifdef IS_LINUX
 RENAME_BORINGSSL_SYMBOLS = yes
 endif