[WebAssembly] Add --[no]-export-dynamic to replace --export-default

In a very recent change I introduced a --no-export-default flag
but after conferring with others it seems that this feature already
exists in gnu GNU ld and lld in the form the --export-dynamic flag
which is off by default.

This change replaces export-default with export-dynamic and also
changes the default to match the traditional linker behaviour.

Now, by default, only the entry point is exported.  If other symbols
are required by the embedder then --export-dynamic or --export can
be used to export all visibility hidden symbols or individual
symbols respectively.

This change touches a lot of tests that were relying on symbols
being exported by default.  I imagine it will also effect many
users but do think the change is worth it match of the traditional
behaviour and flag names.

Differential Revision: https://reviews.llvm.org/D52587

llvm-svn: 343265

1 files changed, 10 insertions, 3 deletions

diff --git a/lld/wasm/Driver.cpp b/lld/wasm/Driver.cpp
index 89785587304..7165f75227e 100644
--- a/lld/wasm/Driver.cpp
+++ b/lld/wasm/Driver.cpp
@@ -373,8 +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->ExportDynamic = Args.hasFlag(OPT_export_dynamic,
+      OPT_no_export_dynamic, false);
   Config->ExportTable = Args.hasArg(OPT_export_table);
   errorHandler().FatalWarnings =
       Args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
@@ -473,6 +473,11 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
     WasmSym::DsoHandle = Symtab->addSyntheticDataSymbol(
         "__dso_handle", WASM_SYMBOL_VISIBILITY_HIDDEN);
     WasmSym::DataEnd = Symtab->addSyntheticDataSymbol("__data_end", 0);
+
+    // These two synthetic symbols exist purely for the embedder so we always
+    // want to export them.
+    WasmSym::HeapBase->ForceExport = true;
+    WasmSym::DataEnd->ForceExport = true;
   }
 
   createFiles(Args);
@@ -507,7 +512,9 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
 
     if (!Config->Entry.empty()) {
       EntrySym = handleUndefined(Config->Entry);
-      if (!EntrySym)
+      if (EntrySym && EntrySym->isDefined())
+        EntrySym->ForceExport = true;
+      else
         error("entry symbol not defined (pass --no-entry to supress): " +
               Config->Entry);
     }