build: support setting an emulator from configure script

V8’s JIT infrastructure requires binaries such as mksnapshot to be run
during the build. However, these binaries must have the same bit-width
as the host platform (e.g. a x86_64 build platform targeting ARMv6 needs
to produce a 32-bit binary).
To work around this issue, allow building the binaries for the host
platform and running them on the build platform with an emulator.
Based on Buildroot’s nodejs-src 0001-add-qemu-wrapper-support.patch.
https://gitlab.com/buildroot.org/buildroot/-/blob/c1d5eada4d4db9eeaa1c44dd1dea95a67c8a70ca/package/nodejs/nodejs-src/0001-add-qemu-wrapper-support.patch
PR-URL: #53899
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Aviv Keller <me@aviv.sh>

Author: tie

common.gypi

@@ -14,6 +14,7 @@
 'enable_pgo_use%': '0',
 'clang_profile_lib%': '',
 'python%': 'python',
+'emulator%': [],
 
 'node_shared%': 'false',
 'node_enable_experimentals%': 'false',

configure.py

@@ -117,6 +117,12 @@
 choices=valid_arch,
 help=f"CPU architecture to build for ({', '.join(valid_arch)})")
 
+parser.add_argument('--emulator',
+action='store',
+dest='emulator',
+default=None,
+help='emulator command that can run executables built for the target system')
+
 parser.add_argument('--cross-compiling',
 action='store_true',
 dest='cross_compiling',
@@ -2633,6 +2639,14 @@ def make_bin_override():
 # will fail to run python scripts.
 gyp_args+= ['-Dpython='+python]
 
+ifoptions.emulatorisnotNone:
+ifnotoptions.cross_compiling:
+# Note that emulator is a list so we have to quote the variable.
+gyp_args+= ['-Demulator='+shlex.quote(options.emulator)]
+else:
+# TODO: perhaps use emulator for tests?
+warn('The `--emulator` option has no effect when cross-compiling.')
+
 ifoptions.use_ninja:
 gyp_args+= ['-f', 'ninja-'+flavor]
 elifflavor=='win'andsys.platform!='msys':

node.gyp

@@ -750,6 +750,7 @@
 '<(SHARED_INTERMEDIATE_DIR)/node_snapshot.cc',
  ],
 'action': [
+'<@(emulator)',
 '<(node_mksnapshot_exec)',
 '--build-snapshot',
 '<(node_snapshot_main)',
@@ -769,6 +770,7 @@
 '<(SHARED_INTERMEDIATE_DIR)/node_snapshot.cc',
  ],
 'action': [
+'<@(emulator)',
 '<@(_inputs)',
 '<@(_outputs)',
  ],
@@ -1105,6 +1107,7 @@
 '<(SHARED_INTERMEDIATE_DIR)/node_javascript.cc',
  ],
 'action': [
+'<@(emulator)',
 '<(node_js2c_exec)',
 '<@(_outputs)',
 'lib',
@@ -1685,6 +1688,7 @@
 '<(PRODUCT_DIR)/<(node_core_target_name).def',
  ],
 'action': [
+'<@(emulator)',
 '<(PRODUCT_DIR)/gen_node_def.exe',
 '<@(_inputs)',
 '<@(_outputs)',

tools/v8_gypfiles/v8.gyp

@@ -144,6 +144,7 @@
 '<@(torque_outputs_inc)',
  ],
 'action': [
+'<@(emulator)',
 '<(PRODUCT_DIR)/<(EXECUTABLE_PREFIX)torque<(EXECUTABLE_SUFFIX)',
 '-o', '<(SHARED_INTERMEDIATE_DIR)/torque-generated',
 '-v8-root', '<(V8_ROOT)',
@@ -264,6 +265,7 @@
 'action': [
 '<(python)',
 '<(V8_ROOT)/tools/run.py',
+'<@(emulator)',
 '<@(_inputs)',
 '<@(_outputs)',
  ],
@@ -492,6 +494,7 @@
  }],
  ],
 'action': [
+'<@(emulator)',
 '>@(_inputs)',
 '>@(mksnapshot_flags)',
  ],
@@ -1981,6 +1984,7 @@
 'action': [
 '<(python)',
 '<(V8_ROOT)/tools/run.py',
+'<@(emulator)',
 '<@(_inputs)',
 '<@(_outputs)',
  ],