[PATCH] [ELF] Add --allow-multiple-definition option.

[Rui Ueyama]

Hi Bigcheese,

If --allow-multiple-definition option is given, LLD does not treat duplicate
symbol error as a fatal error. GNU LD supports this option.

http://llvm-reviews.chandlerc.com/D3211

Files:
  include/lld/Core/LinkingContext.h
  lib/Core/LinkingContext.cpp
  lib/Core/SymbolTable.cpp
  lib/Driver/GnuLdDriver.cpp
  lib/Driver/GnuLdOptions.td
  test/elf/allowduplicates.objtxt

Index: include/lld/Core/LinkingContext.h
===================================================================
--- include/lld/Core/LinkingContext.h
+++ include/lld/Core/LinkingContext.h
@@ -190,6 +190,7 @@
   }
 
   void setDeadStripping(bool enable) { _deadStrip = enable; }
+  void setAllowDuplicates(bool enable) { _allowDuplicates = enable; }
   void setGlobalsAreDeadStripRoots(bool v) { _globalsAreDeadStripRoots = v; }
   void setSearchArchivesToOverrideTentativeDefinitions(bool search) {
     _searchArchivesToOverrideTentativeDefinitions = search;
@@ -212,6 +213,10 @@
   void setAllowShlibUndefines(bool allow) { _allowShlibUndefines = allow; }
   void setLogInputFiles(bool log) { _logInputFiles = log; }
 
+  // Returns true if multiple definitions should not be treated as a
+  // fatal error.
+  bool getAllowDuplicates() const { return _allowDuplicates; }
+
   void appendLLVMOption(const char *opt) { _llvmOptions.push_back(opt); }
   virtual void setInputGraph(std::unique_ptr<InputGraph> inputGraph) {
     _inputGraph = std::move(inputGraph);
@@ -332,6 +337,7 @@
   StringRef _outputPath;
   StringRef _entrySymbolName;
   bool _deadStrip;
+  bool _allowDuplicates;
   bool _globalsAreDeadStripRoots;
   bool _searchArchivesToOverrideTentativeDefinitions;
   bool _searchSharedLibrariesToOverrideTentativeDefinitions;
Index: lib/Core/LinkingContext.cpp
===================================================================
--- lib/Core/LinkingContext.cpp
+++ lib/Core/LinkingContext.cpp
@@ -17,7 +17,8 @@
 namespace lld {
 
 LinkingContext::LinkingContext()
-    : _deadStrip(false), _globalsAreDeadStripRoots(false),
+    : _deadStrip(false), _allowDuplicates(false),
+      _globalsAreDeadStripRoots(false),
       _searchArchivesToOverrideTentativeDefinitions(false),
       _searchSharedLibrariesToOverrideTentativeDefinitions(false),
       _warnIfCoalesableAtomsHaveDifferentCanBeNull(false),
Index: lib/Core/SymbolTable.cpp
===================================================================
--- lib/Core/SymbolTable.cpp
+++ lib/Core/SymbolTable.cpp
@@ -217,7 +217,9 @@
                    << ":"
                    << newAtom.file().path()
                    << "\n";
-      llvm::report_fatal_error("duplicate symbol error");
+      if (!_context.getAllowDuplicates())
+        llvm::report_fatal_error("duplicate symbol error");
+      useNew = false;
       break;
     }
     break;
Index: lib/Driver/GnuLdDriver.cpp
===================================================================
--- lib/Driver/GnuLdDriver.cpp
+++ lib/Driver/GnuLdDriver.cpp
@@ -323,6 +323,10 @@
       ctx->setUseShlibUndefines(true);
       break;
 
+    case OPT_allow_multiple_definition:
+      ctx->setAllowDuplicates(true);
+      break;
+
     case OPT_dynamic_linker:
       ctx->setInterpreter(inputArg->getValue());
       break;
Index: lib/Driver/GnuLdOptions.td
===================================================================
--- lib/Driver/GnuLdOptions.td
+++ lib/Driver/GnuLdOptions.td
@@ -187,6 +187,9 @@
 def use_shlib_undefs: Flag<["--"], "use-shlib-undefines">,
     HelpText<"Resolve undefined symbols from dynamic libraries">,
     Group<grp_resolveropt>;
+def allow_multiple_definition: Flag<["--"], "allow-multiple-definition">,
+    HelpText<"Allow multiple definitions">,
+    Group<grp_resolveropt>;
 
 //===----------------------------------------------------------------------===//
 /// Custom Options
Index: test/elf/allowduplicates.objtxt
===================================================================
--- /dev/null
+++ test/elf/allowduplicates.objtxt
@@ -0,0 +1,48 @@
+# RUN: lld -flavor gnu -target x86_64 --allow-multiple-definition -r %s \
+# RUN:     --output-filetype=yaml | FileCheck %s
+#
+# RUN: not lld -flavor gnu -target x86_64 -r %s --output-filetype=yaml 2>&1 \
+# RUN:   | FileCheck -check-prefix=ERROR %s
+
+---
+defined-atoms:
+  - name:            .text
+    alignment:       2^4
+    section-choice:  custom-required
+    section-name:    .text
+  - name:            main
+    scope:           global
+    content:         [ B8, 00, 00, 00, 00, C7, 44, 24, FC, 00, 00, 00,
+                       00, C3 ]
+    alignment:       2^4
+    section-choice:  custom-required
+    section-name:    .text
+---
+defined-atoms:
+  - name:            .text
+    alignment:       2^4
+    section-choice:  custom-required
+    section-name:    .text
+  - name:            main
+    scope:           global
+    content:         [ B8, 00, 00, 00, 00, C7, 44, 24, FC, 00, 00, 00,
+                       00, C3 ]
+    alignment:       2^4
+    section-choice:  custom-required
+    section-name:    .text
+---
+
+# CHECK: defined-atoms:
+# CHECK:   - name:            .text
+# CHECK:     alignment:       2^4
+# CHECK:     section-choice:  custom-required
+# CHECK:     section-name:    .text
+# CHECK:   - name:            main
+# CHECK:     scope:           global
+# CHECK:     content:         [ B8, 00, 00, 00, 00, C7, 44, 24, FC, 00, 00, 00,
+# CHECK:                        00, C3 ]
+# CHECK:     alignment:       2^4
+# CHECK:     section-choice:  custom-required
+# CHECK:     section-name:    .text
+
+# ERROR: duplicate symbol error
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