Do not re-download Linux kernel tarball (#12)

Author: atrosinenko

build.sh

@@ -66,12 +66,24 @@ fetch_sources() {
   fetch_git_commit "$ROOT/src/llvm" "$llvm_repo" "$LLVM_BRANCH" "$LLVM_SHA"
   fetch_git_commit "$ROOT/src/musl" "$musl_repo" "$MUSL_BRANCH" "$MUSL_SHA"
 
-  local SOURCE_TARBALL=linux-$LINUX_KERNEL_VERSION.tar.xz
-  curl -sSL "https://cdn.kernel.org/pub/linux/kernel/v${LINUX_KERNEL_VERSION%%.*}.x/$SOURCE_TARBALL" \
-       -o "$ROOT/src/$SOURCE_TARBALL"
+  local LOCAL_TARBALL_PATH="$ROOT/src/$LINUX_KERNEL_TARBALL_BASENAME"
+  if [ ! -f "$LOCAL_TARBALL_PATH" ]; then
+    echo "Missing $LOCAL_TARBALL_PATH, downloading from $LINUX_KERNEL_TARBALL_URL..."
+    curl -sSL "$LINUX_KERNEL_TARBALL_URL" -o "$LOCAL_TARBALL_PATH"
+  fi
 
   check_repo_sha "$ROOT/src/llvm" "$LLVM_SHA"
   check_repo_sha "$ROOT/src/musl" "$MUSL_SHA"
+
+  local computed_sha256="$(sha256sum "$LOCAL_TARBALL_PATH" | sed 's/[ \t].*$//')"
+  if [ "$computed_sha256" = "$LINUX_KERNEL_SHA256" ]; then
+    echo "Checked SHA256 of $LOCAL_TARBALL_PATH"
+  else
+    echo "Unexpected SHA256 of $LOCAL_TARBALL_PATH:"
+    echo "  expected: $LINUX_KERNEL_SHA256"
+    echo "  computed: $computed_sha256"
+    exit 1
+  fi
 }
 
 build_in_docker() {

scripts/build-linux-header.sh

@@ -5,8 +5,7 @@ cd "$(dirname "$0")"
 . ./global-vars
 
 KERNEL_ARCH=arm64
-TARBALL_BASENAME="linux-$LINUX_KERNEL_VERSION.tar.xz"
-TARBALL_PATH="$SRC_DIR/$TARBALL_BASENAME"
+TARBALL_PATH="$SRC_DIR/$LINUX_KERNEL_TARBALL_BASENAME"
 
 mkdir "$BUILD_DIR"
 tar -axf "$TARBALL_PATH" -C "$BUILD_DIR" --strip 1

scripts/global-vars

@@ -32,6 +32,9 @@ fi
 # Any recent version should work, so this variable is defined here instead
 # of $REPO_ROOT/config.
 LINUX_KERNEL_VERSION=6.1.58
+LINUX_KERNEL_TARBALL_BASENAME="linux-$LINUX_KERNEL_VERSION.tar.xz"
+LINUX_KERNEL_TARBALL_URL="https://cdn.kernel.org/pub/linux/kernel/v${LINUX_KERNEL_VERSION%%.*}.x/$LINUX_KERNEL_TARBALL_BASENAME"
+LINUX_KERNEL_SHA256=ce987ed3d2f640b3a2a62a0a8573d538a36dfd3cc31e2d7a239ce5a16c1c21ad
 
 CPU_COUNT="$(nproc)"