[lld-macho] Add support for exporting no symbols

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. Differential Revision: https://reviews.llvm.org/D127562
llvm · Jun 15, 2022 · 272bf0f · 272bf0f
1 parent 3cd5696
commit 272bf0f
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Showing 4 changed files with 42 additions and 7 deletions.
diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
@@ -185,6 +185,7 @@ struct Configuration {
   SectionRenameMap sectionRenameMap;
   SegmentRenameMap segmentRenameMap;
 
+  bool hasExplicitExports = false;
   SymbolPatterns exportedSymbols;
   SymbolPatterns unexportedSymbols;
   SymbolPatterns whyLive;

diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
@@ -1403,15 +1403,18 @@ bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
     config->segmentProtections.push_back({segName, maxProt, initProt});
   }
 
+  config->hasExplicitExports =
+      args.hasArg(OPT_no_exported_symbols) ||
+      args.hasArgNoClaim(OPT_exported_symbol, OPT_exported_symbols_list);
   handleSymbolPatterns(args, config->exportedSymbols, OPT_exported_symbol,
                        OPT_exported_symbols_list);
   handleSymbolPatterns(args, config->unexportedSymbols, OPT_unexported_symbol,
                        OPT_unexported_symbols_list);
-  if (!config->exportedSymbols.empty() && !config->unexportedSymbols.empty()) {
-    error("cannot use both -exported_symbol* and -unexported_symbol* options\n"
-          ">>> ignoring unexports");
-    config->unexportedSymbols.clear();
-  }
+  if (config->hasExplicitExports && !config->unexportedSymbols.empty())
+    error("cannot use both -exported_symbol* and -unexported_symbol* options");
+
+  if (args.hasArg(OPT_no_exported_symbols) && !config->exportedSymbols.empty())
+    error("cannot use both -exported_symbol* and -no_exported_symbols options");
 
   // Imitating LD64's:
   // -non_global_symbols_no_strip_list and -non_global_symbols_strip_list can't
@@ -1555,7 +1558,7 @@ bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
     createSyntheticSections();
     createSyntheticSymbols();
 
-    if (!config->exportedSymbols.empty()) {
+    if (config->hasExplicitExports) {
       parallelForEach(symtab->getSymbols(), [](Symbol *sym) {
         if (auto *defined = dyn_cast<Defined>(sym)) {
           StringRef symbolName = defined->getName();

diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
@@ -483,6 +483,9 @@ def exported_symbols_list : Separate<["-"], "exported_symbols_list">,
     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">,

diff --git a/lld/test/MachO/export-options.s b/lld/test/MachO/export-options.s
@@ -9,9 +9,26 @@
 # 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
+#
+# RUN: not %lld -dylib %t/default.o -o /dev/null \
+# RUN:         -no_exported_symbols -exported_symbol b 2>&1 | \
+# RUN:     FileCheck --check-prefix=CONFLICT-NO-EXPORTS %s
+#
+# RUN: not %lld -dylib %t/default.o -o /dev/null \
+# RUN:         -no_exported_symbols -exported_symbols_list %t/literals.txt 2>&1 | \
+# RUN:     FileCheck --check-prefix=CONFLICT-NO-EXPORTS %s
 
 # CONFLICT: error: cannot use both -exported_symbol* and -unexported_symbol* options
-# CONFLICT-NEXT: >>> ignoring unexports
+
+# CONFLICT-NO-EXPORTS: error: cannot use both -exported_symbol* and -no_exported_symbols options
 
 ## Check that an exported literal name with no symbol definition yields an error
 ## but that an exported glob-pattern with no matching symbol definition is OK
@@ -162,6 +179,17 @@
 # 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