[PATCH] D127562: [lld-macho] Add support for exporting no symbols

[Keith Smiley via Phabricator via llvm-commits]

keith created this revision.
Herald added projects: lld-macho, All.
Herald added a reviewer: lld-macho.
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As an optimization for ld64 sometimes it can be useful to not export any
symbols for top level binaries that don't need any exports, to do this
you can pass `-exported_symbols_list /dev/null`, or new with Xcode 14
(ld64 816) there is a `-no_exported_symbols` flag for the same behavior.
This reproduces this behavior where previously an empty exported symbols
list file would have been ignored.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127562

Files:
  lld/MachO/Driver.cpp
  lld/MachO/Options.td
  lld/test/MachO/export-options.s


Index: lld/test/MachO/export-options.s
===================================================================
--- lld/test/MachO/export-options.s
+++ lld/test/MachO/export-options.s
@@ -9,6 +9,14 @@
 # RUN: not %lld -dylib %t/default.o -o /dev/null \
 # RUN:         -exported_symbol a -unexported_symbol b 2>&1 | \
 # RUN:     FileCheck --check-prefix=CONFLICT %s
+#
+# RUN: not %lld -dylib %t/default.o -o /dev/null \
+# RUN:         -exported_symbols_list /dev/null -unexported_symbol b 2>&1 | \
+# RUN:     FileCheck --check-prefix=CONFLICT %s
+#
+# RUN: not %lld -dylib %t/default.o -o /dev/null \
+# RUN:         -no_exported_symbols -unexported_symbol b 2>&1 | \
+# RUN:     FileCheck --check-prefix=CONFLICT %s
 
 # CONFLICT: error: cannot use both -exported_symbol* and -unexported_symbol* options
 # CONFLICT-NEXT: >>> ignoring unexports
@@ -162,6 +170,17 @@
 # AUTOHIDE-PRIVATE: error: cannot export hidden symbol _foo
 # AUTOHIDE-PRIVATE-DEAD-STRIP: (__TEXT,__text) non-external (was a private external) _foo
 
+## Test not exporting any symbols
+# RUN: %lld -dylib %t/symdefs.o -o %t/noexports -exported_symbols_list /dev/null
+# RUN: llvm-objdump --macho --exports-trie %t/noexports | FileCheck --check-prefix=NOEXPORTS %s
+# RUN: %lld -dylib %t/symdefs.o -o %t/noexports -no_exported_symbols
+# RUN: llvm-objdump --macho --exports-trie %t/noexports | FileCheck --check-prefix=NOEXPORTS %s
+
+# NOEXPORTS-NOT: globby_also
+# NOEXPORTS-NOT: globby_only
+# NOEXPORTS-NOT: literal_also
+# NOEXPORTS-NOT: literal_only
+
 #--- default.s
 
 .globl _keep_globl, _hide_globl
Index: lld/MachO/Options.td
===================================================================
--- lld/MachO/Options.td
+++ lld/MachO/Options.td
@@ -483,6 +483,9 @@
     MetaVarName<"<file>">,
     HelpText<"Symbols specified in <file> remain global, while others become private externs">,
     Group<grp_resolve>;
+def no_exported_symbols : Flag<["-"], "no_exported_symbols">,
+    HelpText<"Don't export any symbols from the binary, useful for main executables that don't have plugins">,
+    Group<grp_resolve>;
 def unexported_symbol : Separate<["-"], "unexported_symbol">,
     MetaVarName<"<symbol>">,
     HelpText<"Global <symbol> becomes private extern">,
Index: lld/MachO/Driver.cpp
===================================================================
--- lld/MachO/Driver.cpp
+++ lld/MachO/Driver.cpp
@@ -1405,7 +1405,12 @@
                        OPT_exported_symbols_list);
   handleSymbolPatterns(args, config->unexportedSymbols, OPT_unexported_symbol,
                        OPT_unexported_symbols_list);
-  if (!config->exportedSymbols.empty() && !config->unexportedSymbols.empty()) {
+  bool emptyExportedSymbolsList =
+      args.hasArg(OPT_exported_symbols_list) && config->exportedSymbols.empty();
+  bool exportNoSymbols =
+      emptyExportedSymbolsList || args.hasArg(OPT_no_exported_symbols);
+  if ((!config->exportedSymbols.empty() || exportNoSymbols) &&
+      !config->unexportedSymbols.empty()) {
     error("cannot use both -exported_symbol* and -unexported_symbol* options\n"
           ">>> ignoring unexports");
     config->unexportedSymbols.clear();
@@ -1553,7 +1558,7 @@
     createSyntheticSections();
     createSyntheticSymbols();
 
-    if (!config->exportedSymbols.empty()) {
+    if (!config->exportedSymbols.empty() || exportNoSymbols) {
       parallelForEach(symtab->getSymbols(), [](Symbol *sym) {
         if (auto *defined = dyn_cast<Defined>(sym)) {
           StringRef symbolName = defined->getName();


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