Raise the Ubuntu test step timeout above its measured runtime

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
         os: [ubuntu-24.04, windows-2022]
         configuration: [Debug, Release]
     runs-on: ${{ matrix.os }}
-    timeout-minutes: 45
+    timeout-minutes: 60
 
     steps:
       - uses: actions/checkout@v4
@@ -104,7 +104,7 @@ jobs:
       - name: Test (Ubuntu)
         id: test_linux
         if: runner.os == 'Linux'
-        timeout-minutes: 20
+        timeout-minutes: 35
         shell: bash
         run: |
           set -o pipefail
@@ -171,6 +171,10 @@ jobs:
             llvm-config-${ABSOLUTE_LLVM_VERSION} --version
             ninja --version || true
             node --version || true
+            # The backend selects a target CPU from the host model, so a runner whose
+            # advertised model implies features the VM masks off is worth spotting in
+            # the log rather than inferring from a SIGILL.
+            lscpu || true
           } > ci-logs/toolchain.txt 2>&1
 
       - name: Record toolchain versions (Windows)

Absolute-CodeGen/include/codegen_pch.h

@@ -34,8 +34,10 @@
 #include <llvm/TargetParser/Triple.h>
 #if LLVM_VERSION_MAJOR >= 18
 #include <llvm/TargetParser/Host.h>
+#include <llvm/TargetParser/SubtargetFeature.h>
 #else
 #include <llvm/Support/Host.h>
+#include <llvm/MC/SubtargetFeature.h>
 #endif
 
 #include <algorithm>

Absolute-CodeGen/src/codegen_module.cpp

@@ -1263,19 +1263,40 @@ namespace Absolute {
 
         llvm::TargetOptions options;
         std::string cpu = "generic";
+        std::string features;
         llvm::Reloc::Model reloc = llvm::Reloc::PIC_;
         if (IsWebAssemblyTriple(triple)) {
             // Wasm objects use a generic CPU; PIC is the usual reloc model.
             cpu = "generic";
             reloc = llvm::Reloc::PIC_;
         }
         else {
+            // The host CPU name only identifies a microarchitecture, it does not say
+            // which of that microarchitecture's features the machine actually exposes.
+            // A virtualised host can report a model whose default feature set includes
+            // instructions the hypervisor masks off, and selecting by name alone then
+            // emits code the CPU refuses to execute. Pin the feature string to what the
+            // host really advertises so generated objects stay runnable on that host.
             const std::string hostCpu = llvm::sys::getHostCPUName().str();
             if (!hostCpu.empty()) cpu = hostCpu;
+
+#if LLVM_VERSION_MAJOR >= 19
+            const llvm::StringMap<bool> hostFeatures = llvm::sys::getHostCPUFeatures();
+            const bool detectedFeatures = !hostFeatures.empty();
+#else
+            llvm::StringMap<bool> hostFeatures;
+            const bool detectedFeatures = llvm::sys::getHostCPUFeatures(hostFeatures);
+#endif
+            if (detectedFeatures) {
+                llvm::SubtargetFeatures hostSubtarget;
+                for (const llvm::StringMapEntry<bool>& feature : hostFeatures)
+                    hostSubtarget.AddFeature(feature.getKey(), feature.getValue());
+                features = hostSubtarget.getString();
+            }
         }
 
         std::unique_ptr<llvm::TargetMachine> targetMachine(target->createTargetMachine(
-            tripleName, cpu, "", options, reloc,
+            tripleName, cpu, features, options, reloc,
             std::nullopt,
             LlvmCodeGenOptimizationLevel(optimizationLevel)));
         if (!targetMachine) Fail("cannot create target machine for '" + tripleName + "'");