Handle multi-arch sysroots on Apple platforms

Modules/Platform/Darwin-Initialize.cmake

@@ -133,7 +133,86 @@ function(_apple_resolve_sdk_path sdk_name ret)
   )
   set(${ret} "${_stdout}" PARENT_SCOPE)
 endfunction()
+# Handle multi-arch sysroots. Do this before CMAKE_OSX_SYSROOT is
+# transformed into a path, so that we know the sysroot name.
+function(_apple_resolve_multi_arch_sysroots)
+  if(CMAKE_APPLE_ARCH_SYSROOTS)
+    return() # Already cached
+  endif()
+
+  list(LENGTH CMAKE_OSX_ARCHITECTURES _num_archs)
+  if(NOT (_num_archs GREATER 1))
+    return() # Only apply to multi-arch
+  endif()
+
+  if(CMAKE_OSX_SYSROOT STREQUAL "macosx")
+    # macOS doesn't have a simulator sdk / sysroot, so there is no need to handle per-sdk arches.
+    return()
+  endif()
+
+  if(IS_DIRECTORY "${CMAKE_OSX_SYSROOT}")
+    if(NOT CMAKE_OSX_SYSROOT STREQUAL _CMAKE_OSX_SYSROOT_DEFAULT)
+      message(WARNING "Can not resolve multi-arch sysroots with CMAKE_OSX_SYSROOT set to path (${CMAKE_OSX_SYSROOT})")
+    endif()
+    return()
+  endif()
+
+  string(REPLACE "os" "simulator" _simulator_sdk ${CMAKE_OSX_SYSROOT})
+  set(_sdks "${CMAKE_OSX_SYSROOT};${_simulator_sdk}")
+  foreach(sdk ${_sdks})
+    _apple_resolve_sdk_path(${sdk} _sdk_path)
+    if(NOT IS_DIRECTORY "${_sdk_path}")
+      message(WARNING "Failed to resolve SDK path for '${sdk}'")
+      continue()
+    endif()
+
+    execute_process(
+      COMMAND plutil -extract SupportedTargets.${sdk}.Archs json ${_sdk_path}/SDKSettings.plist -o -
+      OUTPUT_VARIABLE _sdk_archs_json
+      OUTPUT_STRIP_TRAILING_WHITESPACE
+      ERROR_VARIABLE _stderr
+      RESULT_VARIABLE _failed
+      )
+    if(_failed)
+      # Failure to extract supported architectures for an SDK means that the installed SDK is old
+      # and does not provide such information (SDKs that come with Xcode >= 10.x started providing
+      # the information). In such a case, return early, and handle multi-arch builds the old way
+      # (no per-sdk arches).
+      return()
+    endif()
+
+    # Poor man's JSON decoding
+    string(REGEX REPLACE "[]\\[\"]" "" _sdk_archs ${_sdk_archs_json})
+    string(REPLACE "," ";" _sdk_archs ${_sdk_archs})
+
+    set(_sdk_archs_${sdk} ${_sdk_archs})
+    set(_sdk_path_${sdk} ${_sdk_path})
+  endforeach()
+
+  foreach(arch ${CMAKE_OSX_ARCHITECTURES})
+    set(_arch_sysroot "")
+    foreach(sdk ${_sdks})
+      list(FIND _sdk_archs_${sdk} ${arch} arch_index)
+      if(NOT arch_index EQUAL -1)
+        set(_arch_sysroot ${_sdk_path_${sdk}})
+        break()
+      endif()
+    endforeach()
+    if(_arch_sysroot)
+      list(APPEND _arch_sysroots ${_arch_sysroot})
+    else()
+      message(WARNING "No SDK found for architecture '${arch}'")
+      list(APPEND _arch_sysroots "") # Placeholder
+    endif()
+  endforeach()
+
+  set(CMAKE_APPLE_ARCH_SYSROOTS "${_arch_sysroots}" CACHE INTERNAL
+    "Architecture dependent sysroots, one per CMAKE_OSX_ARCHITECTURES")
+endfunction()
+
+_apple_resolve_multi_arch_sysroots()
 
+# Transform CMAKE_OSX_SYSROOT to absolute path
 set(_CMAKE_OSX_SYSROOT_PATH "")
 if(CMAKE_OSX_SYSROOT)
   if("x${CMAKE_OSX_SYSROOT}" MATCHES "/")

Source/cmCoreTryCompile.cxx

@@ -51,6 +51,8 @@ static std::string const kCMAKE_OSX_ARCHITECTURES = "CMAKE_OSX_ARCHITECTURES";
 static std::string const kCMAKE_OSX_DEPLOYMENT_TARGET =
   "CMAKE_OSX_DEPLOYMENT_TARGET";
 static std::string const kCMAKE_OSX_SYSROOT = "CMAKE_OSX_SYSROOT";
+static std::string const kCMAKE_APPLE_ARCH_SYSROOTS =
+  "CMAKE_APPLE_ARCH_SYSROOTS";
 static std::string const kCMAKE_POSITION_INDEPENDENT_CODE =
   "CMAKE_POSITION_INDEPENDENT_CODE";
 static std::string const kCMAKE_SYSROOT = "CMAKE_SYSROOT";
@@ -723,6 +725,7 @@ int cmCoreTryCompile::TryCompileCode(std::vector<std::string> const& argv,
       vars.insert(kCMAKE_OSX_ARCHITECTURES);
       vars.insert(kCMAKE_OSX_DEPLOYMENT_TARGET);
       vars.insert(kCMAKE_OSX_SYSROOT);
+      vars.insert(kCMAKE_APPLE_ARCH_SYSROOTS);
       vars.insert(kCMAKE_POSITION_INDEPENDENT_CODE);
       vars.insert(kCMAKE_SYSROOT);
       vars.insert(kCMAKE_SYSROOT_COMPILE);

Source/cmLocalGenerator.cxx

@@ -1771,7 +1771,7 @@ void cmLocalGenerator::AddArchitectureFlags(std::string& flags,
                                             const std::string& lang,
                                             const std::string& config)
 {
-  // Only add macOS specific flags on Darwin platforms (macOS and iOS):
+  // Only add Apple specific flags on Apple platforms
   if (this->Makefile->IsOn("APPLE") && this->EmitUniversalBinaryFlags) {
     std::vector<std::string> archs;
     target->GetAppleArchs(config, archs);
@@ -1790,11 +1790,29 @@ void cmLocalGenerator::AddArchitectureFlags(std::string& flags,
     std::string sysrootFlagVar =
       std::string("CMAKE_") + lang + "_SYSROOT_FLAG";
     const char* sysrootFlag = this->Makefile->GetDefinition(sysrootFlagVar);
-    if (sysrootFlag && *sysrootFlag && sysroot && *sysroot) {
-      flags += " ";
-      flags += sysrootFlag;
-      flags += " ";
-      flags += this->ConvertToOutputFormat(sysroot, SHELL);
+    if (sysrootFlag && *sysrootFlag) {
+      std::vector<std::string> arch_sysroots;
+      if (const char* arch_sysroots_str =
+            this->Makefile->GetDefinition("CMAKE_APPLE_ARCH_SYSROOTS")) {
+        cmExpandList(std::string(arch_sysroots_str), arch_sysroots, true);
+      }
+      if (!arch_sysroots.empty()) {
+        assert(arch_sysroots.size() == archs.size());
+        for (size_t i = 0; i < archs.size(); ++i) {
+          if (arch_sysroots[i].empty()) {
+            continue;
+          }
+          flags += " -Xarch_" + archs[i] + " ";
+          // Combine sysroot flag and path to work with -Xarch
+          std::string arch_sysroot = sysrootFlag + arch_sysroots[i];
+          flags += this->ConvertToOutputFormat(arch_sysroot, SHELL);
+        }
+      } else if (sysroot && *sysroot) {
+        flags += " ";
+        flags += sysrootFlag;
+        flags += " ";
+        flags += this->ConvertToOutputFormat(sysroot, SHELL);
+      }
     }
 
     const char* deploymentTarget =
@@ -1803,7 +1821,6 @@ void cmLocalGenerator::AddArchitectureFlags(std::string& flags,
       std::string("CMAKE_") + lang + "_OSX_DEPLOYMENT_TARGET_FLAG";
     const char* deploymentTargetFlag =
       this->Makefile->GetDefinition(deploymentTargetFlagVar);
-
     if (deploymentTargetFlag && *deploymentTargetFlag && deploymentTarget &&
         *deploymentTarget) {
       flags += " ";