Strip the producers section in --strip-producers (#1875)

WebAssembly/tool-conventions#93 has a summary of emscripten's current thinking on this. For Binaryen, we don't want to do anything to the producers section by default, but do want it to be possible to optionally remove it. To achieve that, this PR

 * creates a --strip-producers pass that removes that section.
 * creates a --strip-debug pass that removes debug info, same as the old --strip, which is still around but deprecated.

A followup in emscripten will use this pass by default.

Author: kripken

src/passes/Strip.cpp

@@ -15,10 +15,12 @@
  */
 
 //
-// Similar to strip-ing a native binary, this removes debug info
-// and related things like source map URLs, names section, etc.
+// Similar to strip-ing a native binary, this family of passes can
+// removes debug info and other things.
 //
 
+#include <functional>
+
 #include "wasm.h"
 #include "wasm-binary.h"
 #include "pass.h"
@@ -28,19 +30,20 @@ using namespace std;
 namespace wasm {
 
 struct Strip : public Pass {
+  // A function that returns true if the method should be removed.
+  typedef std::function<bool (UserSection&)> Decider;
+  Decider decider;
+
+  Strip(Decider decider) : decider(decider) {}
+
   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;
-        }
+        decider
       ),
       sections.end()
     );
@@ -53,8 +56,19 @@ struct Strip : public Pass {
   }
 };
 
-Pass *createStripPass() {
-  return new Strip();
+Pass *createStripDebugPass() {
+  return new Strip([&](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;
+  });
+}
+
+Pass *createStripProducersPass() {
+  return new Strip([&](const UserSection& curr) {
+    return curr.name == BinaryConsts::UserSections::Producers;
+  });
 }
 
 } // namespace wasm

src/passes/pass.cpp

@@ -133,7 +133,9 @@ 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("strip", "deprecated; same as strip-debug", createStripDebugPass);
+  registerPass("strip-debug", "strip debug info (including the names section)", createStripDebugPass);
+  registerPass("strip-producers", "strip the wasm producers section", createStripProducersPass);
   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 local.tees, replacing them with sets and gets", createUnteePass);

src/passes/passes.h

@@ -84,7 +84,8 @@ Pass* createSimplifyLocalsNoNestingPass();
 Pass* createSimplifyLocalsNoTeePass();
 Pass* createSimplifyLocalsNoStructurePass();
 Pass* createSimplifyLocalsNoTeeNoStructurePass();
-Pass* createStripPass();
+Pass* createStripDebugPass();
+Pass* createStripProducersPass();
 Pass* createSouperifyPass();
 Pass* createSouperifySingleUsePass();
 Pass* createSpillPointersPass();

src/wasm-binary.h

@@ -344,6 +344,7 @@ extern const char* Name;
 extern const char* SourceMapUrl;
 extern const char* Dylink;
 extern const char* Linking;
+extern const char* Producers;
 
 enum Subsection {
   NameFunction = 1,

src/wasm/wasm-binary.cpp

@@ -719,7 +719,7 @@ void WasmBinaryBuilder::readUserSection(size_t payloadLen) {
   } else {
     // an unfamiliar custom section
     if (sectionName.equals(BinaryConsts::UserSections::Linking)) {
-      std::cerr << "warning: linking section is present, which binaryen cannot handle yet - relocations will be invalidated!\n";
+      std::cerr << "warning: linking section is present, so this is not a standard wasm file - binaryen cannot handle this properly!\n";
     }
     wasm.userSections.resize(wasm.userSections.size() + 1);
     auto& section = wasm.userSections.back();

src/wasm/wasm.cpp

@@ -31,6 +31,7 @@ const char* Name = "name";
 const char* SourceMapUrl = "sourceMappingURL";
 const char* Dylink = "dylink";
 const char* Linking = "linking";
+const char* Producers = "producers";
 }
 }
 

test/metadatas.wasm

@@ -0,0 +1,10 @@
+(module
+ (type $0 (func))
+ (export "a" (func $0))
+ (func $0 (; 0 ;) (type $0)
+  (nop)
+ )
+ ;; custom section "emscripten_metadata", size 7
+ ;; custom section "producers", size 187
+)
+

test/metadatas.wasm.fromBinary

@@ -0,0 +1,17 @@
+total
+ [funcs]        : 1       
+ [total]        : 1       
+ nop            : 1       
+total
+ [funcs]        : 1       
+ [total]        : 1       
+ nop            : 1       
+(module
+ (type $0 (func))
+ (export "a" (func $0))
+ (func $0 (; 0 ;) (type $0)
+  (nop)
+ )
+ ;; custom section "emscripten_metadata", size 7
+ ;; custom section "producers", size 187
+)