Add --strip that removes debug info (#1787)

This is sort of like --strip on a native binary. The more specific use case for us is e.g. you link with a library that has -g in its CFLAGS, but you don't want debug info in your final executable (I hit this with poppler now). We can make emcc pass this to binaryen if emcc is not building an output with intended debug info.

build-js.sh

@@ -138,6 +138,7 @@ echo "building shared bitcode"
   $BINARYEN_SRC/passes/SpillPointers.cpp \
   $BINARYEN_SRC/passes/SSAify.cpp \
   $BINARYEN_SRC/passes/StackIR.cpp \
+  $BINARYEN_SRC/passes/Strip.cpp \
   $BINARYEN_SRC/passes/TrapMode.cpp \
   $BINARYEN_SRC/passes/Untee.cpp \
   $BINARYEN_SRC/passes/Vacuum.cpp \

src/passes/CMakeLists.txt

@@ -37,6 +37,7 @@ SET(passes_SOURCES
   Print.cpp
   PrintCallGraph.cpp
   StackIR.cpp
+  Strip.cpp
   RedundantSetElimination.cpp
   RelooperJumpThreading.cpp
   ReReloop.cpp

src/passes/Strip.cpp

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2018 WebAssembly Community Group participants
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//
+// Similar to strip-ing a native binary, this removes debug info
+// and related things like source map URLs, names section, etc.
+//
+
+#include "wasm.h"
+#include "wasm-binary.h"
+#include "pass.h"
+
+using namespace std;
+
+namespace wasm {
+
+struct Strip : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    // Remove name and debug sections.
+    auto& sections = module->userSections;
+    sections.erase(
+      std::remove_if(
+        sections.begin(),
+        sections.end(),
+        [&](const UserSection& curr) {
+          return curr.name == BinaryConsts::UserSections::Name ||
+                 curr.name == BinaryConsts::UserSections::SourceMapUrl ||
+                 curr.name.find(".debug") == 0 ||
+                 curr.name.find("reloc..debug") == 0;
+        }
+      ),
+      sections.end()
+    );
+    // Clean up internal data structures.
+    module->clearDebugInfo();
+    for (auto& func : module->functions) {
+      func->clearNames();
+      func->clearDebugInfo();
+    }
+  }
+};
+
+Pass *createStripPass() {
+  return new Strip();
+}
+
+} // namespace wasm

src/passes/pass.cpp

@@ -131,6 +131,7 @@ void PassRegistry::registerPasses() {
   registerPass("souperify-single-use", "emit Souper IR in text form (single-use nodes only)", createSouperifySingleUsePass);
   registerPass("spill-pointers", "spill pointers to the C stack (useful for Boehm-style GC)", createSpillPointersPass);
   registerPass("ssa", "ssa-ify variables so that they have a single assignment", createSSAifyPass);
+  registerPass("strip", "strip debug info (including the names section)", createStripPass);
   registerPass("trap-mode-clamp", "replace trapping operations with clamping semantics", createTrapModeClamp);
   registerPass("trap-mode-js", "replace trapping operations with js semantics", createTrapModeJS);
   registerPass("untee", "removes tee_locals, replacing them with sets and gets", createUnteePass);

src/passes/passes.h

@@ -82,6 +82,7 @@ Pass* createSimplifyLocalsNoNestingPass();
 Pass* createSimplifyLocalsNoTeePass();
 Pass* createSimplifyLocalsNoStructurePass();
 Pass* createSimplifyLocalsNoTeeNoStructurePass();
+Pass* createStripPass();
 Pass* createSouperifyPass();
 Pass* createSouperifySingleUsePass();
 Pass* createSpillPointersPass();

src/tools/wasm-reduce.cpp

@@ -259,6 +259,7 @@ struct Reducer : public WalkerPass<PostWalker<Reducer, UnifiedExpressionVisitor<
       "--reorder-functions",
       "--reorder-locals",
       "--simplify-locals --vacuum",
+      "--strip",
       "--vacuum"
     };
     auto oldSize = file_size(working);

src/wasm.h

@@ -642,6 +642,9 @@ class Function : public Importable {
   Name getLocalNameOrGeneric(Index index);
 
   bool hasLocalName(Index index) const;
+
+  void clearNames();
+  void clearDebugInfo();
 };
 
 // The kind of an import or export.
@@ -792,6 +795,8 @@ class Module {
   void removeGlobal(Name name);
 
   void updateMaps();
+
+  void clearDebugInfo();
 };
 
 } // namespace wasm

src/wasm/wasm.cpp

@@ -638,6 +638,17 @@ Type Function::getLocalType(Index index) {
   }
 }
 
+void Function::clearNames() {
+  localNames.clear();
+}
+
+void Function::clearDebugInfo() {
+  localIndices.clear();
+  debugLocations.clear();
+  prologLocation.clear();
+  epilogLocation.clear();
+}
+
 FunctionType* Module::getFunctionType(Name name) {
   auto iter = functionTypesMap.find(name);
   if (iter == functionTypesMap.end()) {
@@ -811,4 +822,8 @@ void Module::updateMaps() {
   }
 }
 
+void Module::clearDebugInfo() {
+  debugInfoFileNames.clear();
+}
+
 } // namespace wasm

test/passes/strip.bin.txt

@@ -0,0 +1,15 @@
+(module
+ (type $0 (func (result i32)))
+ (import "env" "__linear_memory" (memory $0 0))
+ (import "env" "__indirect_function_table" (table $timport$1 0 anyfunc))
+ (func $0 (; 0 ;) (type $0) (result i32)
+  (local $0 i32)
+  (set_local $0
+   (i32.const 1)
+  )
+  (return
+   (get_local $0)
+  )
+ )
+ ;; custom section "zinking", size 28
+)