[mono][infra] Fix mono-aot-cross build for linux-arm64 using biarch i…

…mage (#91019)

* Use host rootfs when TARGET_BUILD_ARCH matches

eng/pipelines/common/templates/pipeline-with-resources.yml

@@ -15,8 +15,9 @@ resources:
         ROOTFS_DIR: /crossrootfs/armv6
 
     - container: linux_arm64
-      image: mcr.microsoft.com/dotnet-buildtools/prereqs:cbl-mariner-2.0-cross-arm64
+      image: mcr.microsoft.com/dotnet-buildtools/prereqs:cbl-mariner-2.0-cross-biarch-amd64-arm64
       env:
+        ROOTFS_HOST_DIR: /crossrootfs/x64
         ROOTFS_DIR: /crossrootfs/arm64
 
     - container: linux_musl_x64

eng/pipelines/extra-platforms/runtime-extra-platforms-other.yml

@@ -362,7 +362,7 @@ jobs:
     runtimeFlavor: mono
     platforms:
       - linux_x64
-      # - linux_arm64
+      - linux_arm64
     variables:
       - name: timeoutPerTestInMinutes
         value: 60

src/mono/mono.proj

@@ -810,6 +810,16 @@
       <MonoAotCrossOffsetsToolParams Condition="'$(TargetsWasi)' == 'true'" Include="--wasi-sdk=&quot;$([MSBuild]::NormalizePath('$(WASI_SDK_PATH)'))&quot;" />
     </ItemGroup>
 
+    <!--
+    When cross-building, this PropertyGroup sets the MonoCrossDir to use the ROOTFS_HOST_DIR.
+    This is specifically for linux_arm64 image that has both x64 and arm64 rootfs.
+    The runtime is built using the 'ROOTFS_DIR' which points to '/crossrootfs/arm64'.
+    The 'mono-aot-cross' is built using the 'ROOTFS_HOST_DIR' which points to '/crossrootfs/x64'.
+    -->
+    <PropertyGroup Condition="'$(CrossBuild)' == 'true' and '$(ROOTFS_HOST_DIR)' != '' and $(ROOTFS_HOST_DIR.Contains('$(AotHostArchitecture)'))">
+        <MonoCrossDir>$(ROOTFS_HOST_DIR)</MonoCrossDir>
+    </PropertyGroup>
+
     <!-- AOT compiler cross-build options  -->
     <ItemGroup Condition="'$(MonoCrossDir)' != ''">
       <MonoAOTCMakeArgs Include="-DCMAKE_TOOLCHAIN_FILE=$(CrossToolchainFile)" />
@@ -859,7 +869,7 @@
       <_MonoSkipInitCompiler Condition="'$(CrossBuild)' == 'true'">false</_MonoSkipInitCompiler>
       <_MonoAotCrossOffsetsCommand Condition="'$(MonoUseCrossTool)' == 'true'">$(PythonCmd) $(MonoProjectRoot)mono/tools/offsets-tool/offsets-tool.py @(MonoAotCrossOffsetsToolParams, ' ')</_MonoAotCrossOffsetsCommand>
       <_MonoAotCMakeConfigureCommand>cmake @(MonoAOTCMakeArgs, ' ') $(MonoCMakeExtraArgs) &quot;$(MonoProjectRoot.TrimEnd('\/'))&quot;</_MonoAotCMakeConfigureCommand>
-      <_MonoAotCMakeConfigureCommand Condition="'$(_MonoSkipInitCompiler)' != 'true' and '$(HostOS)' != 'windows'">sh -c 'build_arch=&quot;$(_CompilerTargetArch)&quot; compiler=&quot;$(MonoCCompiler)&quot; . &quot;$(RepositoryEngineeringCommonDir)native/init-compiler.sh&quot; &amp;&amp; @(_MonoAotBuildEnv, ' ') $(_MonoAotCMakeConfigureCommand)'</_MonoAotCMakeConfigureCommand>
+      <_MonoAotCMakeConfigureCommand Condition="'$(_MonoSkipInitCompiler)' != 'true' and '$(HostOS)' != 'windows'">sh -c 'build_arch=&quot;$(_CompilerTargetArch)&quot; ROOTFS_DIR=&quot;$(MonoCrossDir)&quot; compiler=&quot;$(MonoCCompiler)&quot; . &quot;$(RepositoryEngineeringCommonDir)native/init-compiler.sh&quot; &amp;&amp; @(_MonoAotBuildEnv, ' ') $(_MonoAotCMakeConfigureCommand)'</_MonoAotCMakeConfigureCommand>
       <_MonoAotCMakeConfigureCommand Condition="'$(_MonoSkipInitCompiler)' == 'true' and '$(HostOS)' != 'windows'">$(_MonoAOTCCOption) $(_MonoAOTCXXOption) @(_MonoAotBuildEnv, ' ') $(_MonoAotCMakeConfigureCommand)</_MonoAotCMakeConfigureCommand>
       <_MonoAotCMakeConfigureCommand Condition="'$(HostOS)' == 'windows'">call &quot;$(RepositoryEngineeringDir)native\init-vs-env.cmd&quot; $(_CompilerTargetArch) &amp;&amp; cd /D &quot;$(MonoObjCrossDir)&quot; &amp;&amp; @(_MonoAotBuildEnv, ' ') $(_MonoAotCMakeConfigureCommand)</_MonoAotCMakeConfigureCommand>
       <_MonoAotCMakeBuildCommand>cmake --build . --target install --config $(Configuration)</_MonoAotCMakeBuildCommand>