[Xamarin.Android.Build.Tasks] Improved NDK version validation in AOT LLVM configuration. (#113)

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=31985.

Author: tritao

src/Xamarin.Android.Build.Tasks/Tasks/Aot.cs

@@ -277,7 +277,7 @@ bool DoExecute () {
 					throw new Exception ("Unsupported Android target architecture ABI: " + abi);
 				}
 
-				if (!NdkUtil.ValidateNdkPlatform (Log, AndroidNdkDirectory, arch, requireLibm:EnableLLVM)) {
+				if (!NdkUtil.ValidateNdkPlatform (Log, AndroidNdkDirectory, arch, enableLLVM:EnableLLVM)) {
 					return false;
 				}
 

src/Xamarin.Android.Build.Tasks/Tasks/MakeBundleNativeCodeExternal.cs

@@ -98,7 +98,7 @@ bool DoExecute ()
 					break;
 				}
 
-				if (!NdkUtil.ValidateNdkPlatform (Log, AndroidNdkDirectory, arch, requireLibm:true)) {
+				if (!NdkUtil.ValidateNdkPlatform (Log, AndroidNdkDirectory, arch, enableLLVM: false)) {
 					return false;
 				}
 

src/Xamarin.Android.Build.Tasks/Tasks/NdkUtils.cs

@@ -16,7 +16,7 @@ namespace Xamarin.Android.Tasks
 {
 	public static class NdkUtil {
 
-		public static bool ValidateNdkPlatform (TaskLoggingHelper log, string ndkPath, AndroidTargetArch arch, bool requireLibm)
+		public static bool ValidateNdkPlatform (TaskLoggingHelper log, string ndkPath, AndroidTargetArch arch, bool enableLLVM)
 		{
 			// Check that we have a compatible NDK version for the targeted ABIs.
 			NdkUtil.NdkVersion ndkVersion;
@@ -30,12 +30,18 @@ public static bool ValidateNdkPlatform (TaskLoggingHelper log, string ndkPath, A
 
 			// NDK r10d is buggy and cannot link x86_64 ABI shared libraries because they are 32-bits.
 			// See https://code.google.com/p/android/issues/detail?id=161421
-			if (requireLibm && ndkVersion.Version == 10 && ndkVersion.Revision == "d" && arch == AndroidTargetArch.X86_64) {
+			if (enableLLVM && ndkVersion.Version == 10 && ndkVersion.Revision == "d" && arch == AndroidTargetArch.X86_64) {
 				log.LogCodedError ("XA3004", "Android NDK r10d is buggy and provides an incompatible x86_64 libm.so. " +
 						"See https://code.google.com/p/android/issues/detail?id=161422.");
 				return false;
 			}
 
+			if (enableLLVM && (ndkVersion.Version < 10 || (ndkVersion.Version == 10 && ndkVersion.Revision[0] < 'd'))) {
+				log.LogMessage (MessageImportance.High,
+						"The detected Android NDK version is incompatible with the targeted LLVM configuration, " +
+						"please upgrade to NDK r10d or newer.");
+			}
+
 			return true;
 		}