[Bazel] Support for feature debug fission in emsdk-bazel-toolchain #1479

bazel/BUILD

@@ -78,6 +78,18 @@ alias(
     }),
 )
 
+alias(
+    name = "dwp_files",
+    actual = select({
+        ":linux": "@emscripten_bin_linux//:dwp_files",
+        ":linux_arm64": "@emscripten_bin_linux_arm64//:dwp_files",
+        ":macos": "@emscripten_bin_mac//:dwp_files",
+        ":macos_arm64": "@emscripten_bin_mac_arm64//:dwp_files",
+        ":windows": "@emscripten_bin_win//:dwp_files",
+        "//conditions:default": ":empty",
+    }),
+)
+
 platform(
     name = "platform_wasm",
     constraint_values = [

bazel/emscripten_deps.bzl

@@ -96,6 +96,13 @@ filegroup(
         ],
     ),
 )
+
+filegroup(
+    name = "dwp_files",
+    srcs = [
+        "bin/llvm-dwp{bin_extension}",
+    ],
+)
 """
 
 def emscripten_deps(emscripten_version = "latest"):

bazel/emscripten_toolchain/BUILD.bazel

@@ -43,12 +43,25 @@ filegroup(
     ],
 )
 
+filegroup(
+    name = "dwp_files",
+    srcs = [
+        "emdwp-emscripten_bin_linux_arm64.sh",
+        "emdwp-emscripten_bin_linux.sh",
+        "emdwp-emscripten_bin_mac_arm64.sh",
+        "emdwp-emscripten_bin_mac.sh",
+        "emdwp-emscripten_bin_win.bat",
+        "@emsdk//:dwp_files",
+    ],
+)
+
 filegroup(
     name = "all_files",
     srcs = [
         ":ar_files",
         ":compiler_files",
         ":linker_files",
+        ":dwp_files",
     ],
 )
 
@@ -75,7 +88,7 @@ cc_toolchain(
     ar_files = ":ar_files",
     as_files = ":empty",
     compiler_files = ":compiler_files",
-    dwp_files = ":empty",
+    dwp_files = ":dwp_files",
     linker_files = ":linker_files",
     objcopy_files = ":empty",
     strip_files = ":empty",

bazel/emscripten_toolchain/emdwp-emscripten_bin_linux.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+#
+#  This script differs in form from emcc.{py,bat}/…, because bazel are limited/bugged in the way of executing dwp tool.
+#  Bazel dwp action configuration does not pass environment variables, so we cannot use them in this script.
+#  For more info, see PR discussion and bazel issue:
+#  - https://github.com/emscripten-core/emsdk/pull/1531#discussion_r1962090650
+#  - https://github.com/bazelbuild/bazel/issues/25336
+#
+
+exec external/emscripten_bin_linux/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_linux_arm64.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+#
+#  This script differs in form from emcc.{py,bat}/…, because bazel are limited/bugged in the way of executing dwp tool.
+#  Bazel dwp action configuration does not pass environment variables, so we cannot use them in this script.
+#  For more info, see PR discussion and bazel issue:
+#  - https://github.com/emscripten-core/emsdk/pull/1531#discussion_r1962090650
+#  - https://github.com/bazelbuild/bazel/issues/25336
+#
+
+exec external/emscripten_bin_linux_arm64/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_mac.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+#
+#  This script differs in form from emcc.{py,bat}/…, because bazel are limited/bugged in the way of executing dwp tool.
+#  Bazel dwp action configuration does not pass environment variables, so we cannot use them in this script.
+#  For more info, see PR discussion and bazel issue:
+#  - https://github.com/emscripten-core/emsdk/pull/1531#discussion_r1962090650
+#  - https://github.com/bazelbuild/bazel/issues/25336
+#
+
+exec external/emscripten_bin_mac/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_mac_arm64.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+#
+#  This script differs in form from emcc.{py,bat}/…, because bazel are limited/bugged in the way of executing dwp tool.
+#  Bazel dwp action configuration does not pass environment variables, so we cannot use them in this script.
+#  For more info, see PR discussion and bazel issue:
+#  - https://github.com/emscripten-core/emsdk/pull/1531#discussion_r1962090650
+#  - https://github.com/bazelbuild/bazel/issues/25336
+#
+
+exec external/emscripten_bin_mac_arm64/bin/llvm-dwp "$@"

bazel/emscripten_toolchain/emdwp-emscripten_bin_win.bat

@@ -0,0 +1,10 @@
+::
+::  This script differs in form from emcc.{py,bat}/…, because bazel are limited/bugged in the way of executing dwp tool.
+::  Bazel dwp action configuration does not pass environment variables, so we cannot use them in this script.
+::  For more info, see PR discussion and bazel issue:
+::  - https://github.com/emscripten-core/emsdk/pull/1531#discussion_r1962090650
+::  - https://github.com/bazelbuild/bazel/issues/25336
+::
+@ECHO OFF
+
+call external\emscripten_bin_win\bin\llvm-dwp %*

bazel/emscripten_toolchain/toolchain.bzl

@@ -72,12 +72,14 @@ def _impl(ctx):
 
     emscripten_dir = ctx.attr.emscripten_binaries.label.workspace_root
     nodejs_path = ctx.file.nodejs_bin.path
+    emscripten_name = ctx.attr.emscripten_binaries.label.workspace_name
 
     builtin_sysroot = emscripten_dir + "/emscripten/cache/sysroot"
 
     emcc_script = "emcc.%s" % ctx.attr.script_extension
     emcc_link_script = "emcc_link.%s" % ctx.attr.script_extension
     emar_script = "emar.%s" % ctx.attr.script_extension
+    emdwp_script = "emdwp-%s.%s" % (emscripten_name, ctx.attr.script_extension)
 
     ################################################################
     # Tools
@@ -99,6 +101,7 @@ def _impl(ctx):
         tool_path(name = "nm", path = "NOT_USED"),
         tool_path(name = "objdump", path = "/bin/false"),
         tool_path(name = "strip", path = "NOT_USED"),
+        tool_path(name = "dwp", path = emdwp_script),
     ]
 
     ################################################################
@@ -460,6 +463,49 @@ def _impl(ctx):
         feature(
             name = "wasm_standalone",
         ),
+        # Support for debug fission. In short, debugging fission should:
+        #   * reduce linking time, RAM usage and disk usage  
+        #   * speed up incremental builds
+        #   * speed up debugger work (reduce startup and breakpoint time)
+        # (to use this, follow the --fission=yes flag)
+        # https://developer.chrome.com/blog/faster-wasm-debugging
+        # https://bazel.build/docs/user-manual#fission
+        feature(
+            name = "per_object_debug_info",
+            flag_sets = [
+                flag_set(
+                    actions = [
+                        ACTION_NAMES.c_compile,
+                        ACTION_NAMES.cpp_compile,
+                        ACTION_NAMES.cpp_module_codegen,
+                        ACTION_NAMES.assemble,
+                        ACTION_NAMES.preprocess_assemble,
+                    ],
+                    flag_groups = [
+                        flag_group(
+                            flags = ["-g", "-gsplit-dwarf", "-gdwarf-5", "-gpubnames"],
+                            expand_if_available = "per_object_debug_info_file",
+                        ),
+                    ],
+                ),
+            ],
+            enabled = True,
+        ),
+        feature(
+            name = "fission_support",
+            flag_sets = [
+                flag_set(
+                    actions = all_link_actions,
+                    flag_groups = [
+                        flag_group(
+                            flags = ["-sWASM_BIGINT"], # WASM_BIGINT required to support dwarf-5
+                            expand_if_available = "is_using_fission",
+                        ),
+                    ],
+                ),
+            ],
+            enabled = True,
+        )
     ]
 
     crosstool_default_flag_sets = [

bazel/emscripten_toolchain/wasm_binary.py

@@ -14,6 +14,7 @@
 import argparse
 import os
 import tarfile
+import shutil
 
 
 def ensure(f):
@@ -26,11 +27,20 @@ def main():
   parser = argparse.ArgumentParser()
   parser.add_argument('--archive', help='The archive to extract from.')
   parser.add_argument('--outputs', help='Comma separated list of files that should be extracted from the archive. Only the extname has to match a file in the archive.')
+  parser.add_argument('--dwp_file', help='Optional dwp input file, generated when fission flags set.')
   parser.add_argument('--allow_empty_outputs', help='If an output listed in --outputs does not exist, create it anyways.', action='store_true')
   args = parser.parse_args()
 
   args.archive = os.path.normpath(args.archive)
   args.outputs = args.outputs.split(",")
+  args.dwp_file = os.path.normpath(args.dwp_file) if args.dwp_file else None
+
+  if args.dwp_file:
+    for idx, output in enumerate(args.outputs):
+      if output.endswith(".dwp"):  # also update extension 'binary.dwp' to 'binary.wasm.dwp'
+        shutil.copy2(args.dwp_file, output)
+        args.outputs.pop(idx)
+        break
 
   tar = tarfile.open(args.archive)
 

bazel/emscripten_toolchain/wasm_cc_binary.bzl

@@ -69,6 +69,7 @@ _ALLOW_OUTPUT_EXTNAMES = [
     ".fetch.js",
     ".js.symbols",
     ".wasm.debug.wasm",
+    ".wasm.dwp",
     ".html",
     ".aw.js",
 ]
@@ -107,10 +108,11 @@ _WASM_BINARY_COMMON_ATTRS = {
 }
 
 def _wasm_cc_binary_impl(ctx):
-    args = ctx.actions.args()
     cc_target = ctx.attr.cc_target[0]
+    dwp_file = cc_target[DebugPackageInfo].dwp_file if DebugPackageInfo in cc_target else None
+    outputs = ctx.outputs.outputs
 
-    for output in ctx.outputs.outputs:
+    for output in outputs:
         valid_extname = False
         for allowed_extname in _ALLOW_OUTPUT_EXTNAMES:
             if output.path.endswith(allowed_extname):
@@ -119,28 +121,35 @@ def _wasm_cc_binary_impl(ctx):
         if not valid_extname:
             fail("Invalid output '{}'. Allowed extnames: {}".format(output.basename, ", ".join(_ALLOW_OUTPUT_EXTNAMES)))
 
+    inputs = ctx.files.cc_target
+    args = ctx.actions.args()
     args.add_all("--archive", ctx.files.cc_target)
-    args.add_joined("--outputs", ctx.outputs.outputs, join_with = ",")
+    args.add_joined("--outputs", outputs, join_with = ",")
+
+    if dwp_file:
+        args.add("--dwp_file", dwp_file)
+        inputs = inputs + [dwp_file]
 
     ctx.actions.run(
-        inputs = ctx.files.cc_target,
-        outputs = ctx.outputs.outputs,
+        inputs = inputs,
+        outputs = outputs,
         arguments = [args],
         executable = ctx.executable._wasm_binary_extractor,
     )
 
     return [
         DefaultInfo(
-            files = depset(ctx.outputs.outputs),
+            files = depset(outputs),
             # This is needed since rules like web_test usually have a data
             # dependency on this target.
-            data_runfiles = ctx.runfiles(transitive_files = depset(ctx.outputs.outputs)),
+            data_runfiles = ctx.runfiles(transitive_files = depset(outputs)),
         ),
         OutputGroupInfo(_wasm_tar = cc_target.files),
     ]
 
 def _wasm_cc_binary_legacy_impl(ctx):
     cc_target = ctx.attr.cc_target[0]
+    dwp_file = cc_target[DebugPackageInfo].dwp_file if DebugPackageInfo in cc_target else None
     outputs = [
         ctx.outputs.loader,
         ctx.outputs.wasm,
@@ -151,17 +160,23 @@ def _wasm_cc_binary_legacy_impl(ctx):
         ctx.outputs.data,
         ctx.outputs.symbols,
         ctx.outputs.dwarf,
+        ctx.outputs.dwp,
         ctx.outputs.html,
         ctx.outputs.audio_worklet,
     ]
 
+    inputs = ctx.files.cc_target
     args = ctx.actions.args()
     args.add("--allow_empty_outputs")
     args.add_all("--archive", ctx.files.cc_target)
     args.add_joined("--outputs", outputs, join_with = ",")
 
+    if dwp_file:
+        args.add("--dwp_file", dwp_file)
+        inputs = inputs + [dwp_file]
+
     ctx.actions.run(
-        inputs = ctx.files.cc_target,
+        inputs = inputs,
         outputs = outputs,
         arguments = [args],
         executable = ctx.executable._wasm_binary_extractor,
@@ -202,6 +217,7 @@ def _wasm_binary_legacy_outputs(name, cc_target):
         "data": "{}/{}.data".format(name, basename),
         "symbols": "{}/{}.js.symbols".format(name, basename),
         "dwarf": "{}/{}.wasm.debug.wasm".format(name, basename),
+        "dwp": "{}/{}.wasm.dwp".format(name, basename),
         "html": "{}/{}.html".format(name, basename),
         "audio_worklet": "{}/{}.aw.js".format(name, basename)
     }