[WebAssembly] Add --export-default/--no-export-default options

These option control weather or not symbols marked as visibility
default are exported in the output binary.

By default this is true, but emscripten prefers to control the
exported symbol list explicitly at link time and ignore the
symbol attributes.

Differential Revision: https://reviews.llvm.org/D52003

llvm-svn: 343034

5 files changed, 26 insertions, 2 deletions

diff --git a/lld/test/wasm/visibility-hidden.ll b/lld/test/wasm/visibility-hidden.ll
index f553c08159c..d1a83cdf407 100644
--- a/lld/test/wasm/visibility-hidden.ll
+++ b/lld/test/wasm/visibility-hidden.ll
@@ -2,11 +2,17 @@
 ; RUN: llc -filetype=obj %S/Inputs/hidden.ll -o %t2.o
 ; RUN: rm -f %t2.a
 ; RUN: llvm-ar rcs %t2.a %t2.o
-; RUN: wasm-ld %t.o %t2.a -o %t.wasm
-; RUN: obj2yaml %t.wasm | FileCheck %s
 
 ; Test that hidden symbols are not exported, whether pulled in from an archive
 ; or directly.
+; RUN: wasm-ld %t.o %t2.a -o %t.wasm
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; Test that symbols with default visitiblity are not exported when
+; --no-export-default is passed.
+; RUN: wasm-ld --no-export-default %t.o %t2.a -o %t.nodef.wasm
+; RUN: obj2yaml %t.nodef.wasm | FileCheck %s -check-prefix=NO-DEFAULT
+
 
 target triple = "wasm32-unknown-unknown"
 
@@ -53,3 +59,11 @@ entry:
 ; CHECK-NEXT:         Kind:            FUNCTION
 ; CHECK-NEXT:         Index:           5
 ; CHECK-NEXT:   - Type:
+
+
+; NO-DEFAULT:        - Type:            EXPORT
+; NO-DEFAULT-NEXT:     Exports:
+; NO-DEFAULT-NEXT:       - Name:            memory
+; NO-DEFAULT-NEXT:         Kind:            MEMORY
+; NO-DEFAULT-NEXT:         Index:           0
+; NO-DEFAULT-NEXT:   - Type:
diff --git a/lld/wasm/Config.h b/lld/wasm/Config.h
index 76a78056707..ae8989f15d7 100644
--- a/lld/wasm/Config.h
+++ b/lld/wasm/Config.h
@@ -24,6 +24,7 @@ struct Configuration {
   bool Demangle;
   bool DisableVerify;
   bool ExportAll;
+  bool ExportDefault;
   bool ExportTable;
   bool GcSections;
   bool ImportMemory;
diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index f477ba3b235..789bda90b1a 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -373,6 +373,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   Config->DisableVerify = Args.hasArg(OPT_disable_verify);
   Config->Entry = getEntry(Args, Args.hasArg(OPT_relocatable) ? "" : "_start");
   Config->ExportAll = Args.hasArg(OPT_export_all);
+  Config->ExportDefault = Args.hasFlag(OPT_export_default,
+      OPT_no_export_default, true);
   Config->ExportTable = Args.hasArg(OPT_export_table);
   errorHandler().FatalWarnings =
       Args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
diff --git a/lld/wasm/Options.td b/lld/wasm/Options.td
index e2922c24c90..e98b1b9f89a 100644
--- a/lld/wasm/Options.td
+++ b/lld/wasm/Options.td
@@ -30,6 +30,10 @@ defm demangle: B<"demangle",
     "Demangle symbol names",
     "Do not demangle symbol names">;
 
+defm export_default: B<"export-default",
+    "Export symbols marked as 'default' visibility (default)",
+    "Do not export symbols marked as 'default' visibility">;
+
 def entry: S<"entry">, MetaVarName<"<entry>">,
   HelpText<"Name of entry point symbol">;
 
diff --git a/lld/wasm/Symbols.cpp b/lld/wasm/Symbols.cpp
index a11081cbcf7..68bcadbb9af 100644
--- a/lld/wasm/Symbols.cpp
+++ b/lld/wasm/Symbols.cpp
@@ -105,6 +105,9 @@ bool Symbol::isExported() const {
   if (ForceExport || Config->ExportAll)
     return true;
 
+  if (!Config->ExportDefault)
+    return false;
+
   return !isHidden();
 }