[compiler-rt][Darwin] Check for arm64 support directly

[smeenai]

Summary

Rather than having to manually map SDK versions to their supported
architectures, just directly ask the SDK which architectures it
supports. This detection is tweaked to use SDKSettings.json to match
Clang (https://reviews.llvm.org/D55673) and reportedly Xcode [1], which
lets us check for architecture support directly instead of relying on
string matching another command's output. I also unified the arm64
checking for all platforms.

[1] https://worthdoingbadly.com/sim-macos-arm-sdk/#what-i-learned

[bc-lee]

It seems that codes for tvos simulator also needs to be modified.

[smeenai]

Adjust tvos simulator architecture detection as well

[smeenai]

In D124557#3478468, @bc-lee wrote:

It seems that codes for tvos simulator also needs to be modified.

Thanks, I'd missed that somehow.

[delcypher]

compiler-rt/cmake/builtin-config-ix.cmake

88

With this implementation we can't tell the difference between the python failing for some other reason (e.g. executable path wrong, SDK JSON file doesn't exist). Are we sure we want that?

101

Any chance you could make the interface like this?

function(darwin_add_arm64_if_supported all_possible_archs os sdk_name)
  set(sdk_path "${DARWIN_${sdk_name}_SYSROOT}")
  # Compute <COMPUTED VAR>
  # ...
  set("${all_possible_archs}" <COMPUTED VAR> PARENT_SCOPE)
endfunction()

which is then called like

darwin_add_arm64_if_supported(DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS ios iphonesimulator)

The changes are basically

• prefix with darwin because the method is actually Darwin specific.
• Don't pass SDK path when only the SDK name is needed.
• Use ordering of arguments that matches Apple's internal code.

[delcypher]

compiler-rt/cmake/builtin-config-ix.cmake

83

@arphaman Do we know when SDKSettings.json was added? If it's not present in older SDKs then we won't be able to build against them with this change.

[delcypher]

@smeenai Thanks for the patch. I think the overall spirit of this change is good. There are just some details to work out which I've left in other comments.

[delcypher]

compiler-rt/cmake/builtin-config-ix.cmake

88

Sorry that should say:

With this implementation we can't tell the difference between the architecture not being supported and python failing for some other reason (e.g. executable path wrong, SDK JSON file doesn't exist).

[steven_wu]

compiler-rt/cmake/builtin-config-ix.cmake

83

I think 10.14 is the first version we have JSON SDKSettings.

[smeenai]

Planning changes to remove from people's queues while I address the comments (which will take a bit, since I'm out next week). Thanks for the reviews!

compiler-rt/cmake/builtin-config-ix.cmake

83

Ah, and I assume that's new enough that we can't rely on this for compiler-rt. That's a bit of a bummer, because reading the JSON directly seemed nicer than parsing the output of another program (especially once we can use string(JSON)), but I can just change this part back (or maybe try the JSON and fall back to the plist if it's not available, but idk if that's overkill; I guess it depends on if the plist will ever go away in the future and if the JSON is considered to be more modern or canonical in any way).

101

Yup, I'm happy to make that change.

[delcypher]

compiler-rt/cmake/builtin-config-ix.cmake

83

Well for Apple internal builds it's fine. We don't build with SDKs that old.

For the greendragon CI (https://green.lab.llvm.org/green/) it says it's using Xcode 11.5 and that comes with the macOS 10.15.4 SDK (https://developer.apple.com/documentation/xcode-release-notes/xcode-11_5-release-notes).

So in principle I think this change "should" be fine. It might be wiser to split this change out in to a separate commit (given that it seems orthagonal) so that you can easily revert that part without needing to revert the rest of your change, just in case something goes wrong.

compiler-rt/cmake/builtin-config-ix.cmake

if(APPLE)
   find_darwin_sdk_dir(DARWIN_ios_SYSROOT iphoneos)
   find_darwin_sdk_dir(DARWIN_watchossim_SYSROOT watchsimulator)
   find_darwin_sdk_dir(DARWIN_watchos_SYSROOT watchos)
   find_darwin_sdk_dir(DARWIN_tvossim_SYSROOT appletvsimulator)
   find_darwin_sdk_dir(DARWIN_tvos_SYSROOT appletvos)
 
   # Get supported architecture from SDKSettings.
   function(sdk_has_arch_support sdk_path os arch has_support)
+    set(sdk_json "${sdk_path}/SDKSettings.json")
+    # We can switch to string(JSON) once our minimum CMake version is 3.19+.
     execute_process(COMMAND
-        /usr/libexec/PlistBuddy -c "Print :SupportedTargets:${os}:Archs" ${sdk_path}/SDKSettings.plist
-      OUTPUT_VARIABLE SDK_SUPPORTED_ARCHS
-      RESULT_VARIABLE PLIST_ERROR
+      "${Python3_EXECUTABLE}" -c
+      # `not in` so that our exit code is 0 (success) if the arch is found
+      "import json; exit('${arch}' not in json.load(open('${sdk_json}'))['SupportedTargets']['${os}']['Archs'])"
+      RESULT_VARIABLE ARCH_FIND_RESULT
       ERROR_QUIET)
-    if (PLIST_ERROR EQUAL 0 AND
-        SDK_SUPPORTED_ARCHS MATCHES " ${arch}\n")
-      message(STATUS "Found ${arch} support in ${sdk_path}/SDKSettings.plist")
+    if (ARCH_FIND_RESULT EQUAL 0)
+      message(STATUS "Found ${arch} support in ${sdk_json}")
       set("${has_support}" On PARENT_SCOPE)
     else()
-      message(STATUS "No ${arch} support in ${sdk_path}/SDKSettings.plist")
+      message(STATUS "No ${arch} support in ${sdk_json}")
       set("${has_support}" Off PARENT_SCOPE)
     endif()
   endfunction()
 
+  # Add support for arm64 if available in SDK.
+  function(add_arm64_if_supported sdk_path os archs_var)
+    set(local_archs ${${archs_var}})
+    foreach(arch ${ARM64})
+      sdk_has_arch_support(${sdk_path} ${os} ${arch} has_support)
+      if(has_support)
+        list(APPEND local_archs ${arch})
+      endif()
+    endforeach()
+    set(${archs_var} ${local_archs} PARENT_SCOPE)
+  endfunction()
+
   set(DARWIN_EMBEDDED_PLATFORMS)
   set(DARWIN_osx_BUILTIN_MIN_VER 10.5)
   set(DARWIN_osx_BUILTIN_MIN_VER_FLAG
       -mmacosx-version-min=${DARWIN_osx_BUILTIN_MIN_VER})
   set(DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
-  # Add support for arm64 macOS if available in SDK.
-  foreach(arch ${ARM64})
-    sdk_has_arch_support(${DARWIN_osx_SYSROOT} macosx ${arch} MACOS_ARM_SUPPORT)
-    if (MACOS_ARM_SUPPORT)
-     list(APPEND DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS ${arch})
-    endif()
-  endforeach(arch)
+  add_arm64_if_supported(${DARWIN_osx_SYSROOT} macosx DARWIN_osx_BUILTIN_ALL_POSSIBLE_ARCHS)
 
   if(COMPILER_RT_ENABLE_IOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS ios)
     set(DARWIN_ios_MIN_VER_FLAG -miphoneos-version-min)
     set(DARWIN_ios_BUILTIN_MIN_VER 6.0)
     set(DARWIN_ios_BUILTIN_MIN_VER_FLAG
       ${DARWIN_ios_MIN_VER_FLAG}=${DARWIN_ios_BUILTIN_MIN_VER})
     set(DARWIN_ios_BUILTIN_ALL_POSSIBLE_ARCHS ${ARM64} ${ARM32})
     set(DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
-    find_darwin_sdk_version(iossim_sdk_version "iphonesimulator")
-    if ("${iossim_sdk_version}" VERSION_GREATER 14.0 OR "${iossim_sdk_version}" VERSION_EQUAL 14.0)
-      list(APPEND DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS arm64)
-    endif()
+    add_arm64_if_supported(${DARWIN_iossim_SYSROOT} iphonesimulator DARWIN_iossim_BUILTIN_ALL_POSSIBLE_ARCHS)
   endif()
   if(COMPILER_RT_ENABLE_WATCHOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS watchos)
     set(DARWIN_watchos_MIN_VER_FLAG -mwatchos-version-min)
     set(DARWIN_watchos_BUILTIN_MIN_VER 2.0)
     set(DARWIN_watchos_BUILTIN_MIN_VER_FLAG
       ${DARWIN_watchos_MIN_VER_FLAG}=${DARWIN_watchos_BUILTIN_MIN_VER})
     set(DARWIN_watchos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 armv7k arm64_32)
     set(DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86})
-    find_darwin_sdk_version(watchossim_sdk_version "watchsimulator")
-    if ("${watchossim_sdk_version}" VERSION_GREATER 7.0 OR "${watchossim_sdk_version}" VERSION_EQUAL 7.0)
-      list(APPEND DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS arm64)
-    endif()
+    add_arm64_if_supported(${DARWIN_watchossim_SYSROOT} watchsimulator DARWIN_watchossim_BUILTIN_ALL_POSSIBLE_ARCHS)
   endif()
   if(COMPILER_RT_ENABLE_TVOS)
     list(APPEND DARWIN_EMBEDDED_PLATFORMS tvos)
     set(DARWIN_tvos_MIN_VER_FLAG -mtvos-version-min)
     set(DARWIN_tvos_BUILTIN_MIN_VER 9.0)
     set(DARWIN_tvos_BUILTIN_MIN_VER_FLAG
       ${DARWIN_tvos_MIN_VER_FLAG}=${DARWIN_tvos_BUILTIN_MIN_VER})
     set(DARWIN_tvos_BUILTIN_ALL_POSSIBLE_ARCHS armv7 arm64)
     set(DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS ${X86} ${X86_64})
-    find_darwin_sdk_version(tvossim_sdk_version "appletvsimulator")
-    if ("${tvossim_sdk_version}" VERSION_GREATER 14.0 OR "${tvossim_sdk_version}" VERSION_EQUAL 14.0)
-      list(APPEND DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS arm64)
-    endif()
+    add_arm64_if_supported(${DARWIN_tvossim_SYSROOT} appletvsimulator DARWIN_tvossim_BUILTIN_ALL_POSSIBLE_ARCHS)
   endif()
 
   set(BUILTIN_SUPPORTED_OS osx)
 
   # We're setting the flag manually for each target OS
   set(CMAKE_OSX_DEPLOYMENT_TARGET "")
 
   # NOTE: We deliberately avoid using `DARWIN_<os>_ARCHS` here because that is