Add GitHub Actions CI to build and test via QEMU

This commit introduces a GitHub Actions workflow to build the Linmo
kernel using the GNU RISC-V toolchain and run selected applications
(e.g., cpubench) using QEMU.

Test output is extracted from QEMU logs and automatically posted
as a comment to pull requests. Toolchain setup, kernel build, and
QEMU test execution have been modularized into reusable scripts
under the `.ci/` directory.

Features:
- CI supports running multiple apps in a single job
- All QEMU runs are time-limited to prevent hangs
- Results are reported directly to GitHub PRs

Limitations:
- Only GNU toolchain is supported (LLVM is a work in progress)
- Some test apps (e.g., cpubench) do not exit cleanly due to
  entering preemptive scheduler mode

Fixes: #2
Supersedes: #11

Author: G36maid

.ci/run-qemu-tests.sh

@@ -0,0 +1,49 @@
+#!/bin/bash
+set -e
+export CROSS_COMPILE=${CROSS_COMPILE:-riscv32-unknown-elf-}
+
+# Check if at least one app is provided
+if [ $# -eq 0 ]; then
+    echo "Usage: $0 <app1> [app2] [app3] ..."
+    echo "Example: $0 hello echo cpubench"
+    exit 1
+fi
+
+APPS="$@"
+TIMEOUT=10
+
+echo "[+] Will run apps: $APPS"
+echo ""
+
+# Loop through each app
+for app in $APPS; do
+    echo "=== Running $app ==="
+
+    # Build the app
+    echo "[+] Building $app..."
+    make clean >/dev/null 2>&1
+    if ! make "$app" >/dev/null 2>&1; then
+        echo "[!] Failed to build $app"
+        echo ""
+        continue
+    fi
+
+    # Run in QEMU with timeout
+    echo "[+] Running $app in QEMU (timeout: ${TIMEOUT}s)..."
+    set +e
+    timeout ${TIMEOUT}s qemu-system-riscv32 -nographic -machine virt -bios none -kernel build/image.elf
+    exit_code=$?
+    set -e
+
+    # Print result
+    if [ $exit_code -eq 124 ]; then
+        echo "[!] $app timed out"
+    elif [ $exit_code -eq 0 ]; then
+        echo "[✓] $app completed successfully"
+    else
+        echo "[!] $app failed with exit code $exit_code"
+    fi
+    echo ""
+done
+
+echo "[+] All apps tested"

.ci/setup-toolchain.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+set -e
+
+URL="https://github.com/riscv-collab/riscv-gnu-toolchain/releases/download/2025.06.13/riscv32-elf-ubuntu-22.04-gcc-nightly-2025.06.13-nightly.tar.xz"
+
+echo "[+] Downloading RISC-V GNU toolchain..."
+wget "$URL"
+tar -xf "$(basename "$URL")"
+
+echo "[+] Exporting toolchain path..."
+echo "$PWD/riscv/bin" >> "$GITHUB_PATH"

.github/workflows/ci.yml

@@ -0,0 +1,59 @@
+name: Linmo CI
+
+on:
+  push:
+    branches: [main, ci]
+  pull_request:
+    branches: [main, ci]
+
+jobs:
+  basic-tests:
+    runs-on: ubuntu-24.04
+    name: Basic Tests
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y build-essential qemu-system-riscv32 wget
+
+      - name: Setup RISC-V Toolchain
+        run: .ci/setup-toolchain.sh
+
+      - name: Verify toolchain installation
+        run: |
+          riscv32-unknown-elf-gcc --version
+          qemu-system-riscv32 --version
+        env:
+          CROSS_COMPILE: riscv32-unknown-elf-
+
+      - name: Build Kernel
+        run: |
+          make clean
+          make
+        env:
+          CROSS_COMPILE: riscv32-unknown-elf-
+
+      - name: Run Basic Apps
+        id: test
+        run: |
+          output=$(.ci/run-qemu-tests.sh cpubench test64)
+          echo "TEST_OUTPUT<<EOF" >> $GITHUB_OUTPUT
+          echo "$output" >> $GITHUB_OUTPUT
+          echo "EOF" >> $GITHUB_OUTPUT
+
+      - name: Comment PR with results
+        if: github.event_name == 'pull_request'
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const output = `${{ steps.test.outputs.TEST_OUTPUT }}`;
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: `## Linmo QEMU App Test Result\n\n\`\`\`\n${output}\n\`\`\`\n\n_This is an automated report from CI._`
+            });