Add manually overriding of the darwin SDK version

[vchuravy]

Summary

When doing cross-compilation from Linux to MacOS we don't have
access to have access to xcodebuild and therefore need a way
to set the SDK version from the outside.

Fixes https://reviews.llvm.org/D68292#1853594 for me.

[delcypher]

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

47–51

I do not want to support a cached SDK version. A variable that if set provides an override is fine but CMake's caching causes far too many problems already that I don't want a new one introduced.

So something like this...

if (DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION)
  message(WARNING "Overriding ${sdk_name} SDK version to ${DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION}")
  set(${var} "${DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION}")
  return()
endif()

I'd consider a reasonable compromise.

Then in your CMake invocations you can provide something like -DDARWIN_macosx_OVERRIDE_SDK_VERSION=10.12.

82

You deleted a comment where I explicitly stated we do not want to use the cache. This goes completely against that. Caching the SDK version will create too many problems.

[delcypher]

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

47–51

Sorry that should be

if (DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION)
  message(WARNING "Overriding ${sdk_name} SDK version to ${DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION}")
  set(${var} "${DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION}" PARENT_SCOPE)
  return()
endif()

[vchuravy]

Allow for manually specifying the darwin SDK version

[vchuravy]

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

47–51

Thanks! Manually overriding is fine for my use-case.

[delcypher]

@vchuravy LGTM. Just to note an alternative to this patch would be to implement a "barebones" version of xcrun that implements enough functionality to report the SDK to CMake. I think the compromise we came to is fine for now. If this patch becomes a maintenance burden in the future then we may need to revisit this.

compiler-rt/cmake/Modules/CompilerRTDarwinUtils.cmake

function(find_darwin_sdk_dir var sdk_name)
   if(result_process EQUAL 0)
     set(${var} ${var_internal} PARENT_SCOPE)
   endif()
   message(STATUS "Checking DARWIN_${sdk_name}_SYSROOT - '${var_internal}'")
   set(DARWIN_${sdk_name}_CACHED_SYSROOT ${var_internal} CACHE STRING "Darwin SDK path for SDK ${sdk_name}." FORCE)
 endfunction()
 
 function(find_darwin_sdk_version var sdk_name)
-  # We deliberately don't cache the result here because
-  # CMake's caching causes too many problems.
+  if (DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION)
+    message(WARNING "Overriding ${sdk_name} SDK version to ${DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION}")
+    set(${var} "${DARWIN_${sdk_name}_OVERRIDE_SDK_VERSION}" PARENT_SCOPE)
+    return()
+  endif()
   set(result_process 1)
   if(NOT DARWIN_PREFER_PUBLIC_SDK)
     # Let's first try the internal SDK, otherwise use the public SDK.
     execute_process(
       COMMAND xcrun --sdk ${sdk_name}.internal --show-sdk-version
       RESULT_VARIABLE result_process
       OUTPUT_VARIABLE var_internal
       OUTPUT_STRIP_TRAILING_WHITESPACE
message(FATAL_ERROR
       "Failed to determine SDK version for \"${sdk_name}\" SDK")
   endif()
   # Check reported version looks sane.
   if (NOT "${var_internal}" MATCHES "^[0-9]+\\.[0-9]+(\\.[0-9]+)?$")
     message(FATAL_ERROR
       "Reported SDK version \"${var_internal}\" does not look like a version")
   endif()
   set(${var} ${var_internal} PARENT_SCOPE)
 endfunction()
 
 # There isn't a clear mapping of what architectures are supported with a given
 # target platform, but ld's version output does list the architectures it can
 # link for.
 function(darwin_get_toolchain_supported_archs output_var)
   execute_process(
     COMMAND "${CMAKE_LINKER}" -v
     ERROR_VARIABLE LINKER_VERSION)