[WebAssembly] Add --export flag to force a symbol to be exported

This is useful for emscripten or other tools that want to
selectively exports symbols without necessarily changing the
source code.

Differential Revision: https://reviews.llvm.org/D42003

1 files changed, 13 insertions, 4 deletions

diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 0173cdc09e5..75c3cb56aa5 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -296,8 +296,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
       addSyntheticUndefinedFunction(Config->Entry, &Signature);
 
     // Handle the `--undefined <sym>` options.
-    for (StringRef S : args::getStrings(Args, OPT_undefined))
-      addSyntheticUndefinedFunction(S, nullptr);
+    for (auto* Arg : Args.filtered(OPT_undefined))
+      addSyntheticUndefinedFunction(Arg->getValue(), nullptr);
 
     Config->CtorSymbol = Symtab->addDefinedFunction(
         "__wasm_call_ctors", &Signature, WASM_SYMBOL_VISIBILITY_HIDDEN);
@@ -321,8 +321,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
     // -u/--undefined since these undefined symbols have only names and no
     // function signature, which means they cannot be written to the final
     // output.
-    for (StringRef S : args::getStrings(Args, OPT_undefined)) {
-      Symbol *Sym = Symtab->find(S);
+    for (auto* Arg : Args.filtered(OPT_undefined)) {
+      Symbol *Sym = Symtab->find(Arg->getValue());
       if (!Sym->isDefined())
         error("function forced with --undefined not found: " + Sym->getName());
     }
@@ -330,6 +330,15 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   if (errorCount())
     return;
 
+  for (auto *Arg : Args.filtered(OPT_export)) {
+    Symbol *Sym = Symtab->find(Arg->getValue());
+    if (!Sym || !Sym->isDefined())
+      error("symbol exported via --export not found: " +
+            Twine(Arg->getValue()));
+    else
+      Sym->setHidden(false);
+  }
+
   if (!Config->Entry.empty() && !Symtab->find(Config->Entry)->isDefined())
     error("entry point not found: " + Config->Entry);
   if (errorCount())