[core] support .gnu.linkonce sections

.gnu.linkonce sections are similar to section groups. They were supported before
section groups existed and provided a way to resolve COMDAT sections using a
different design. There are few implementations that use .gnu.linkonce sections
to store simple floating point constants which doesnot require complex section
group support but need a way to store only one copy of the floating point
constant. .gnu.linkonce based symbol resolution achieves that.

llvm-svn: 205163

11 files changed, 597 insertions, 11 deletions

diff --git a/lld/include/lld/Core/DefinedAtom.h b/lld/include/lld/Core/DefinedAtom.h
index de325ada4b8..b911d2323b1 100644
--- a/lld/include/lld/Core/DefinedAtom.h
+++ b/lld/include/lld/Core/DefinedAtom.h
@@ -147,6 +147,7 @@ public:
     typeRWNote,             // Identifies readwrite note sections [ELF]
     typeNoAlloc,            // Identifies non allocatable sections [ELF]
     typeGroupComdat,        // Identifies a section group [ELF, COFF]
+    typeGnuLinkOnce,        // Identifies a gnu.linkonce section [ELF]
   };
 
   // Permission bits for atoms and segments. The order of these values are
diff --git a/lld/include/lld/Core/Resolver.h b/lld/include/lld/Core/Resolver.h
index 006ed6e0e79..b6d8185b3cd 100644
--- a/lld/include/lld/Core/Resolver.h
+++ b/lld/include/lld/Core/Resolver.h
@@ -67,8 +67,8 @@ public:
 private:
   typedef std::function<void(StringRef, bool)> UndefCallback;
 
-  /// \brief Add section group if it does not exist previously.
-  void maybeAddSectionGroup(const DefinedAtom &atom);
+  /// \brief Add section group/.gnu.linkonce if it does not exist previously.
+  bool maybeAddSectionGroupOrGnuLinkOnce(const DefinedAtom &atom);
 
   /// \brief The main function that iterates over the files to resolve
   bool resolveUndefines();
diff --git a/lld/lib/Core/DefinedAtom.cpp b/lld/lib/Core/DefinedAtom.cpp
index 8362aadb21c..806bd6f4521 100644
--- a/lld/lib/Core/DefinedAtom.cpp
+++ b/lld/lib/Core/DefinedAtom.cpp
@@ -72,6 +72,7 @@ DefinedAtom::ContentPermissions DefinedAtom::permissions(ContentType type) {
     return permRW_L;
 
   case typeGroupComdat:
+  case typeGnuLinkOnce:
   case typeUnknown:
   case typeTempLTO:
     return permUnknown;
diff --git a/lld/lib/Core/Resolver.cpp b/lld/lib/Core/Resolver.cpp
index 9555fef22ba..6ff898726b3 100644
--- a/lld/lib/Core/Resolver.cpp
+++ b/lld/lib/Core/Resolver.cpp
@@ -184,11 +184,22 @@ void Resolver::doUndefinedAtom(const UndefinedAtom &atom) {
 }
 
 /// \brief Add the section group and the group-child reference members.
-void Resolver::maybeAddSectionGroup(const DefinedAtom &atom) {
+bool Resolver::maybeAddSectionGroupOrGnuLinkOnce(const DefinedAtom &atom) {
   // First time adding a group ?
   bool isFirstTime = _symbolTable.addGroup(atom);
-  if (!isFirstTime)
-    return;
+
+  if (!isFirstTime) {
+    // If duplicate symbols are allowed, select the first group.
+    if (_context.getAllowDuplicates())
+      return true;
+    const DefinedAtom *prevGroup = llvm::dyn_cast<DefinedAtom>(_symbolTable.findGroup(atom.name()));
+    assert(prevGroup && "Internal Error: The group atom could only be a defined atom");
+    // The atoms should be of the same content type, reject invalid group
+    // resolution behaviors.
+    if (atom.contentType() != prevGroup->contentType())
+      return false;
+    return true;
+  }
 
   for (const Reference *r : atom) {
     if ((r->kindNamespace() == lld::Reference::KindNamespace::all) &&
@@ -200,6 +211,7 @@ void Resolver::maybeAddSectionGroup(const DefinedAtom &atom) {
       _symbolTable.add(*target);
     }
   }
+  return true;
 }
 
 // called on each atom when a file is added
@@ -229,8 +241,14 @@ void Resolver::doDefinedAtom(const DefinedAtom &atom) {
   // add to list of known atoms
   _atoms.push_back(&atom);
 
-  if (atom.contentType() == DefinedAtom::typeGroupComdat)
-    maybeAddSectionGroup(atom);
+  if ((atom.contentType() == DefinedAtom::typeGroupComdat) ||
+      (atom.contentType() == DefinedAtom::typeGnuLinkOnce)) {
+    // Raise error if there exists a similar gnu linkonce section.
+    if (!maybeAddSectionGroupOrGnuLinkOnce(atom)) {
+      llvm::errs() << "SymbolTable: error while merging " << atom.name() << "\n";
+      llvm::report_fatal_error("duplicate symbol error");
+    }
+  }
   else
     _symbolTable.add(atom);
 
diff --git a/lld/lib/ReaderWriter/Native/WriterNative.cpp b/lld/lib/ReaderWriter/Native/WriterNative.cpp
index 9735783b0a9..c1173380faa 100644
--- a/lld/lib/ReaderWriter/Native/WriterNative.cpp
+++ b/lld/lib/ReaderWriter/Native/WriterNative.cpp
@@ -41,7 +41,8 @@ public:
       // We are trying to process all atoms, but the defined() iterator does not
       // return group children. So, when a group parent is found, we need to
       // handle each child atom.
-      if (defAtom->contentType() == DefinedAtom::typeGroupComdat) {
+      if (defAtom->contentType() == DefinedAtom::typeGroupComdat ||
+          defAtom->contentType() == DefinedAtom::typeGnuLinkOnce) {
         for (const Reference *r : *defAtom) {
           if (r->kindNamespace() != lld::Reference::KindNamespace::all)
             continue;
diff --git a/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp b/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
index 49de7f551cf..b2295f87d66 100644
--- a/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
+++ b/lld/lib/ReaderWriter/YAML/ReaderWriterYAML.cpp
@@ -71,7 +71,9 @@ public:
       if (!atom->name().empty())
         buildDuplicateNameMap(*atom);
 
-      if (atom->contentType() == DefinedAtom::typeGroupComdat) {
+      if (atom->contentType() == DefinedAtom::typeGroupComdat ||
+          atom->contentType() == DefinedAtom::typeGnuLinkOnce) {
+
         for (const lld::Reference *ref : *atom) {
           if (ref->kindNamespace() != lld::Reference::KindNamespace::all)
             continue;
@@ -229,7 +231,8 @@ private:
     }
 
     if (const lld::DefinedAtom *da = dyn_cast<DefinedAtom>(atom)) {
-      if (da->contentType() == DefinedAtom::typeGroupComdat) {
+      if (da->contentType() == DefinedAtom::typeGroupComdat ||
+          da->contentType() == DefinedAtom::typeGnuLinkOnce) {
         if (_groupMap.count(name)) {
           _io.setError(Twine("duplicate group name: ") + name);
         } else {
@@ -476,7 +479,8 @@ template <> struct ScalarEnumerationTraits<lld::DefinedAtom::ContentType> {
     io.enumCase(value, "ro-note",         DefinedAtom::typeRONote);
     io.enumCase(value, "rw-note",         DefinedAtom::typeRWNote);
     io.enumCase(value, "no-alloc",        DefinedAtom::typeNoAlloc);
-    io.enumCase(value, "group-comdat", DefinedAtom::typeGroupComdat);
+    io.enumCase(value, "group-comdat",    DefinedAtom::typeGroupComdat);
+    io.enumCase(value, "gnu-linkonce",    DefinedAtom::typeGnuLinkOnce);
   }
 };
 
diff --git a/lld/test/core/gnulinkonce-rearrange-resolve.objtxt b/lld/test/core/gnulinkonce-rearrange-resolve.objtxt
new file mode 100644
index 00000000000..dbcc95591a9
--- /dev/null
+++ b/lld/test/core/gnulinkonce-rearrange-resolve.objtxt
@@ -0,0 +1,115 @@
+# RUN: lld -core %s | FileCheck %s
+
+#
+# Test that gnu linkonce sections are parsed and the first section selected for symbol
+# resolution
+#
+
+---
+defined-atoms:
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+---
+defined-atoms:
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+...
+
+# CHECK: defined-atoms:
+# CHECK:   - name:            g1
+# CHECK:     ref-name:        [[PARENT:[a-zA-Z\.0-9_]+]]
+# CHECK:     type:            gnu-linkonce
+# CHECK:     references:
+# CHECK:       - kind:            group-child
+# CHECK:         target:          f1
+# CHECK:       - kind:            group-child
+# CHECK:         target:          f2
+# CHECK:       - kind:            group-child
+# CHECK:         target:          [[CHILD:[a-zA-Z\.0-9_]+]]
+# CHECK:       - kind:            group-child
+# CHECK:         target:          d1
+# CHECK:   - name:            f1
+# CHECK:     references:
+# CHECK:       - kind:            group-parent
+# CHECK:         target:          [[PARENT]]
+# CHECK:   - name:            f2
+# CHECK:     references:
+# CHECK:       - kind:            group-parent
+# CHECK:         target:          [[PARENT]]
+# CHECK:   - name:            g1
+# CHECK:     ref-name:        [[CHILD]]
+# CHECK:     references:
+# CHECK:       - kind:            group-parent
+# CHECK:         target:          [[PARENT]]
+# CHECK:   - name:            d1
+# CHECK:     references:
+# CHECK:       - kind:            group-parent
+# CHECK:         target:          [[PARENT]]
diff --git a/lld/test/core/gnulinkonce-remaining-undef.objtxt b/lld/test/core/gnulinkonce-remaining-undef.objtxt
new file mode 100644
index 00000000000..ee5f681ac02
--- /dev/null
+++ b/lld/test/core/gnulinkonce-remaining-undef.objtxt
@@ -0,0 +1,113 @@
+# RUN: lld -core %s | FileCheck %s
+
+#
+# Test that gnu linkonce sections are parsed and the first section selected for
+# symbol resolution. The second file which has the same gnu linkonce section has
+# a unresolved undefined symbol. lets make sure that the symbol is kept around
+# in the final link and remains undefined.
+#
+
+---
+defined-atoms:
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+---
+defined-atoms:
+  - name:            anotherfunction
+    scope:           global
+    type:            data
+    references:
+      - kind:            layout-before
+        target:          f3
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f3
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          f3
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+undefined-atoms:
+    - name:              f3
+      can-be-null:       never
+...
+
+#CHECK:   - name:            anotherfunction
+#CHECK:     scope:           global
+#CHECK:     type:            data
+#CHECK:     references:
+#CHECK:       - kind:            layout-before
+#CHECK:         offset:          0
+#CHECK:         target:          f3
+#CHECK: undefined-atoms:
+#CHECK:   - name:            f3
diff --git a/lld/test/core/gnulinkonce-resolve.objtxt b/lld/test/core/gnulinkonce-resolve.objtxt
new file mode 100644
index 00000000000..ff099a5ba9d
--- /dev/null
+++ b/lld/test/core/gnulinkonce-resolve.objtxt
@@ -0,0 +1,133 @@
+# RUN: lld -core %s | FileCheck %s
+
+#
+# Test that gnu linkonce sections are parsed and the first section selected for symbol
+# resolution
+#
+
+---
+defined-atoms:
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+---
+defined-atoms:
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+...
+
+#CHECK: defined-atoms:
+#CHECK:   - name:            g1
+#CHECK:     ref-name:        [[PARENT:[a-zA-Z\.0-9_]+]]
+#CHECK:     scope:           global
+#CHECK:     type:            gnu-linkonce
+#CHECK:     references:
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDONE:[a-zA-Z\.0-9_]+]]
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDTWO:[a-zA-Z\.0-9_]+]]
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDTHREE:[a-zA-Z\.0-9_]+]]
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDFOUR:[a-zA-Z\.0-9_]+]]
+#CHECK:   - name:            f1
+#CHECK:     ref-name:        [[GCHILDONE]]
+#CHECK:     scope:           global
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            f2
+#CHECK:     ref-name:        [[GCHILDTWO]]
+#CHECK:     scope:           global
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            g1
+#CHECK:     ref-name:        [[GCHILDTHREE]]
+#CHECK:     scope:           global
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            d1
+#CHECK:     ref-name:        [[GCHILDFOUR]]
+#CHECK:     scope:           global
+#CHECK:     type:            data
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK: ...
diff --git a/lld/test/core/gnulinkonce-simple.objtxt b/lld/test/core/gnulinkonce-simple.objtxt
new file mode 100644
index 00000000000..1a96b62669b
--- /dev/null
+++ b/lld/test/core/gnulinkonce-simple.objtxt
@@ -0,0 +1,112 @@
+# RUN: lld -core %s | FileCheck %s
+
+#
+# Test that gnu linkonce sections are parsed properly when there is a reference to a
+# atom from outside the gnu linkonce section.
+#
+
+---
+defined-atoms:
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          d1
+      - kind:            group-child
+        target:          g1
+  - name:            anotherfunction
+    scope:           global
+    type:            data
+    references:
+      - kind:            layout-before
+        target:          f1
+
+undefined-atoms:
+    - name:              f1
+      can-be-null:       never
+...
+
+#CHECK: defined-atoms:
+#CHECK:   - name:            g1
+#CHECK:     ref-name:        [[PARENT:[a-zA-Z\.0-9_]+]]
+#CHECK:     scope:           global
+#CHECK:     type:            gnu-linkonce
+#CHECK:     references:
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDONE:[a-zA-Z\.0-9_]+]]
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDTWO:[a-zA-Z\.0-9_]+]]
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDTHREE:[a-zA-Z\.0-9_]+]]
+#CHECK:       - kind:            group-child
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDFOUR:[a-zA-Z\.0-9_]+]]
+#CHECK:   - name:            f1
+#CHECK:     ref-name:        [[GCHILDONE]]
+#CHECK:     scope:           global
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            f2
+#CHECK:     ref-name:        [[GCHILDTWO]]
+#CHECK:     scope:           global
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            d1
+#CHECK:     ref-name:        [[GCHILDTHREE]]
+#CHECK:     scope:           global
+#CHECK:     type:            data
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            g1
+#CHECK:     ref-name:        [[GCHILDFOUR]]
+#CHECK:     scope:           global
+#CHECK:     references:
+#CHECK:       - kind:            group-parent
+#CHECK:         offset:          0
+#CHECK:         target:          [[PARENT]]
+#CHECK:   - name:            anotherfunction
+#CHECK:     scope:           global
+#CHECK:     type:            data
+#CHECK:     references:
+#CHECK:       - kind:            layout-before
+#CHECK:         offset:          0
+#CHECK:         target:          [[GCHILDONE]]
+#CHECK: ...
diff --git a/lld/test/core/sectiongroup-gnulinkonce-error.objtxt b/lld/test/core/sectiongroup-gnulinkonce-error.objtxt
new file mode 100644
index 00000000000..e54cdfe0571
--- /dev/null
+++ b/lld/test/core/sectiongroup-gnulinkonce-error.objtxt
@@ -0,0 +1,88 @@
+# RUN: not lld -core %s 2>&1 | FileCheck %s
+
+#
+# Test that section groups/gnu linkonce sections are parsed and a merge error 
+# is displayed at the time of symbol resolution.
+#
+
+---
+defined-atoms:
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            group-comdat
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+---
+defined-atoms:
+  - name:            f1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            f2
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            code
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            d1
+    scope:           global
+    type:            data
+    references:
+      - kind:            group-parent
+        target:          g1
+  - name:            g1
+    scope:           global
+    type:            gnu-linkonce
+    references:
+      - kind:            group-child
+        target:          f1
+      - kind:            group-child
+        target:          f2
+      - kind:            group-child
+        target:          g1
+      - kind:            group-child
+        target:          d1
+...
+
+#CHECK: SymbolTable: error while merging g1
+#CHECK: LLVM ERROR: duplicate symbol error
+