build: add --write-snapshot-as-array-literals to configure.py

This makes it easier to locate indeterminism in the snapshot, with
the following command:

$ ./configure --write-snapshot-as-array-literals
$ make V=
$ mv out/Release/obj/gen/node_snapshot.cc ./node_snapshot.cc
$ make V=
$ diff out/Release/obj/gen/node_snapshot.cc ./node_snapshot.cc

PR-URL: #49312
Refs: nodejs/build#3043
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

configure.py

@@ -609,6 +609,14 @@
     default=None,
     help='Use Link Time Code Generation. This feature is only available on Windows.')
 
+parser.add_argument('--write-snapshot-as-array-literals',
+    action='store_true',
+    dest='write_snapshot_as_array_literals',
+    default=None,
+    help='Write the snapshot data as array literals for readability.'
+         'By default the snapshot data may be written as string literals on some '
+         'platforms to speed up compilation.')
+
 parser.add_argument('--without-node-snapshot',
     action='store_true',
     dest='without_node_snapshot',
@@ -1290,6 +1298,11 @@ def configure_node(o):
     o['variables']['node_use_node_code_cache'] = b(
       not cross_compiling and not options.shared)
 
+  if options.write_snapshot_as_array_literals is not None:
+     o['variables']['node_write_snapshot_as_array_literals'] = b(options.write_snapshot_as_array_literals)
+  else:
+     o['variables']['node_write_snapshot_as_array_literals'] = b(flavor != 'mac' and flavor != 'linux')
+
   if target_arch == 'arm':
     configure_arm(o)
   elif target_arch in ('mips', 'mipsel', 'mips64el'):

node.gyp

@@ -10,6 +10,7 @@
     'node_use_v8_platform%': 'true',
     'node_use_bundled_v8%': 'true',
     'node_shared%': 'false',
+    'node_write_snapshot_as_string_literals': 'true',
     'force_dynamic_crt%': 0,
     'ossfuzz' : 'false',
     'node_module_version%': '',
@@ -1247,8 +1248,8 @@
       ],
 
       'conditions': [
-        ['OS in "linux mac"', {
-          'defines': [ 'NODE_MKSNAPSHOT_USE_STRING_LITERALS=1' ],
+        ['node_write_snapshot_as_array_literals=="true"', {
+          'defines': [ 'NODE_MKSNAPSHOT_USE_ARRAY_LITERALS=1' ],
         }],
         [ 'node_use_openssl=="true"', {
           'defines': [

src/node_snapshot_builder.h

@@ -23,7 +23,7 @@ class NODE_EXTERN_PRIVATE SnapshotBuilder {
       const std::vector<std::string>& args,
       const std::vector<std::string>& exec_args,
       std::optional<std::string_view> main_script_path = std::nullopt,
-      bool use_string_literals = true);
+      bool use_array_literals = false);
 
   // Generate the snapshot into out.
   static ExitCode Generate(SnapshotData* out,

src/node_snapshotable.cc

@@ -773,11 +773,11 @@ void WriteByteVectorLiteral(std::ostream* ss,
                             const T* vec,
                             size_t size,
                             const char* var_name,
-                            bool use_string_literals) {
+                            bool use_array_literals) {
   constexpr bool is_uint8_t = std::is_same_v<T, uint8_t>;
   static_assert(is_uint8_t || std::is_same_v<T, char>);
   constexpr const char* type_name = is_uint8_t ? "uint8_t" : "char";
-  if (use_string_literals) {
+  if (!use_array_literals) {
     const uint8_t* data = reinterpret_cast<const uint8_t*>(vec);
     *ss << "static const " << type_name << " *" << var_name << " = ";
     *ss << (is_uint8_t ? R"(reinterpret_cast<const uint8_t *>(")" : "\"");
@@ -818,7 +818,7 @@ static void WriteCodeCacheInitializer(std::ostream* ss,
 
 void FormatBlob(std::ostream& ss,
                 const SnapshotData* data,
-                bool use_string_literals) {
+                bool use_array_literals) {
   ss << R"(#include <cstddef>
 #include "env.h"
 #include "node_snapshot_builder.h"
@@ -833,7 +833,7 @@ namespace node {
                          data->v8_snapshot_blob_data.data,
                          data->v8_snapshot_blob_data.raw_size,
                          "v8_snapshot_blob_data",
-                         use_string_literals);
+                         use_array_literals);
 
   ss << R"(static const int v8_snapshot_blob_size = )"
      << data->v8_snapshot_blob_data.raw_size << ";\n";
@@ -846,7 +846,7 @@ namespace node {
                            item.data.data,
                            item.data.length,
                            var_name.c_str(),
-                           use_string_literals);
+                           use_array_literals);
   }
 
   ss << R"(const SnapshotData snapshot_data {
@@ -1132,7 +1132,7 @@ ExitCode SnapshotBuilder::GenerateAsSource(
     const std::vector<std::string>& args,
     const std::vector<std::string>& exec_args,
     std::optional<std::string_view> main_script_path,
-    bool use_string_literals) {
+    bool use_array_literals) {
   std::string main_script_content;
   std::optional<std::string_view> main_script_optional;
   if (main_script_path.has_value()) {
@@ -1159,7 +1159,7 @@ ExitCode SnapshotBuilder::GenerateAsSource(
   if (exit_code != ExitCode::kNoFailure) {
     return exit_code;
   }
-  FormatBlob(out, &data, use_string_literals);
+  FormatBlob(out, &data, use_array_literals);
 
   if (!out) {
     std::cerr << "Failed to write to " << out_path << "\n";

tools/snapshot/node_mksnapshot.cc

@@ -79,18 +79,18 @@ int BuildSnapshot(int argc, char* argv[]) {
     out_path = result->args()[1];
   }
 
-#ifdef NODE_MKSNAPSHOT_USE_STRING_LITERALS
-  bool use_string_literals = true;
+#ifdef NODE_MKSNAPSHOT_USE_ARRAY_LITERALS
+  bool use_array_literals = true;
 #else
-  bool use_string_literals = false;
+  bool use_array_literals = false;
 #endif
 
   node::ExitCode exit_code =
       node::SnapshotBuilder::GenerateAsSource(out_path.c_str(),
                                               result->args(),
                                               result->exec_args(),
                                               main_script_path,
-                                              use_string_literals);
+                                              use_array_literals);
 
   node::TearDownOncePerProcess();
   return static_cast<int>(exit_code);