Add cDAC-only CI test legs for Windows and Linux

- SOSRunner sends 'runtimes --forceusecdac' to dotnet-dump when
  SOS_TEST_CDAC is set, enabling cDAC-only mode for dump tests.
- build.yml gains a useCdac parameter that passes -useCdac to
  the build script, setting SOS_TEST_CDAC=true.
- Add Windows_cDAC (build+test) and Ubuntu_22_04_cDAC (test-only)
  CI legs running Release x64 with cDAC-only mode.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Max Charlamb

diagnostics.yml

@@ -94,6 +94,17 @@ extends:
               architecture: arm64
               artifactUploadPath: bin/Windows_NT.arm64.Release
 
+      - ${{ if ne(parameters.buildOnly, true) }}:
+        - template: /eng/pipelines/build.yml
+          parameters:
+            jobTemplate: ${{ variables.jobTemplate }}
+            name: Windows_cDAC
+            osGroup: Windows_NT
+            useCdac: true
+            buildConfigs:
+            - configuration: Release
+              architecture: x64
+
       - template: /eng/pipelines/build.yml
         parameters:
           jobTemplate: ${{ variables.jobTemplate }}
@@ -234,6 +245,19 @@ extends:
               - configuration: Debug
                 architecture: x64
 
+        - template: /eng/pipelines/build.yml
+          parameters:
+            jobTemplate: ${{ variables.jobTemplate }}
+            name: Ubuntu_22_04_cDAC
+            osGroup: Linux
+            container: test_ubuntu_22_04
+            dependsOn: Linux
+            testOnly: true
+            useCdac: true
+            buildConfigs:
+            - configuration: Release
+              architecture: x64
+
         - template: /eng/pipelines/build.yml
           parameters:
             jobTemplate: ${{ variables.jobTemplate }}

eng/pipelines/build.yml

@@ -60,6 +60,11 @@ parameters:
   type: boolean
   default: false
 
+  # Optional: run tests with cDAC-only mode
+- name: useCdac
+  type: boolean
+  default: false
+
 # Optional: architecture cross build if true
 - name: crossBuild
   type: boolean
@@ -144,6 +149,9 @@ jobs:
       - ${{ if eq(parameters.testOnly, 'true') }}:
         - _TestArgs: '-test -skipnative'
 
+      - ${{ if eq(parameters.useCdac, 'true') }}:
+        - _TestArgs: '-test -skipnative -useCdac'
+
       - ${{ if or(eq(parameters.buildOnly, 'true'), eq(parameters.isCodeQLRun, 'true')) }}:
         - _TestArgs: ''
 

src/tests/SOS.UnitTests/SOSRunner.cs

@@ -685,6 +685,10 @@ public static async Task<SOSRunner> StartDebugger(TestInformation information, D
                         && !config.IsPrivateBuildTesting()
                         && !config.IsNightlyBuild();
                     initialCommands.Add($"runtimes --DacSignatureVerification:{(shouldVerifyDacSignature ? "true" : "false")}");
+                    if (config.TestCDAC)
+                    {
+                        initialCommands.Add("runtimes --forceusecdac");
+                    }
                     arguments.Append(debuggerPath);
                     arguments.Append(@" analyze %DUMP_NAME%");
                     debuggerPath = config.DotNetDumpHost();