[PECOFF] Fix alignment bug.

There was a bug that if a section has an alignment requirement and there are
multiple symbols at offset 0 in the section, only the last atom at offset 0
would be aligned properly. That bug would move only the last symbol to an
alignment boundary, leaving other symbols unaligned, although they should be at
the same location. That caused a mysterious SEGV error of the resultant
executable.

With this patch, we manage all symbols at the same location properly, rather
than keeping the last one.

llvm-svn: 190724

lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp

@@ -478,7 +478,7 @@ private:
           COFFDefinedAtom(*this, "", sectionName, Atom::scopeTranslationUnit,
                           type, perms, _merge[section], data, 0);
       atoms.push_back(atom);
-      _definedAtomLocations[section][0] = atom;
+      _definedAtomLocations[section][0].push_back(atom);
       return error_code::success();
     }
 
@@ -491,7 +491,7 @@ private:
           COFFDefinedAtom(*this, "", sectionName, Atom::scopeTranslationUnit,
                           type, perms, _merge[section], data, ++ordinal);
       atoms.push_back(atom);
-      _definedAtomLocations[section][0] = atom;
+      _definedAtomLocations[section][0].push_back(atom);
     }
 
     for (auto si = symbols.begin(), se = symbols.end(); si != se; ++si) {
@@ -505,12 +505,12 @@ private:
                           type, perms, _merge[section], data, ++ordinal);
       atoms.push_back(atom);
       _symbolAtom[*si] = atom;
-      _definedAtomLocations[section][(*si)->Value] = atom;
+      _definedAtomLocations[section][(*si)->Value].push_back(atom);
     }
 
     // Finally, set alignment to the first atom so that the section contents
     // will be aligned as specified by the object section header.
-    _definedAtomLocations[section][0]->setAlignment(getAlignment(section));
+    _definedAtomLocations[section][0][0]->setAlignment(getAlignment(section));
     return error_code::success();
   }
 
@@ -542,7 +542,8 @@ private:
                         COFFDefinedFileAtom *&result, uint32_t &offsetInAtom) {
     for (auto i : _definedAtomLocations[section]) {
       uint32_t atomAddress = i.first;
-      COFFDefinedAtom *atom = i.second;
+      std::vector<COFFDefinedAtom *> &atomsAtSameLocation = i.second;
+      COFFDefinedAtom *atom = atomsAtSameLocation.back();
       if (atomAddress <= targetAddress &&
           targetAddress < atomAddress + atom->size()) {
         result = atom;
@@ -697,7 +698,8 @@ private:
 
   // A sorted map to find an atom from a section and an offset within
   // the section.
-  std::map<const coff_section *, std::map<uint32_t, COFFDefinedAtom *> >
+  std::map<const coff_section *,
+           std::map<uint32_t, std::vector<COFFDefinedAtom *> > >
   _definedAtomLocations;
 
   mutable llvm::BumpPtrAllocator _alloc;

lld/test/pecoff/Inputs/alignment.obj.yaml

@@ -0,0 +1,48 @@
+---
+header:
+  Machine:         IMAGE_FILE_MACHINE_I386
+  Characteristics: [  ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       256
+    SectionData:     5589E583EC14C745FC00000000C744240C00000000C744240807000000C744240400000000C7042400000000FF150000000083EC1031C083C4145DC3
+    Relocations:
+      - VirtualAddress:  25
+        SymbolName:      .data
+        Type:            IMAGE_REL_I386_DIR32
+      - VirtualAddress:  33
+        SymbolName:      .data
+        Type:            IMAGE_REL_I386_DIR32
+  - Name:            .text$1
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       4096
+    SectionData:     00
+  - Name:            .data
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+    Alignment:       4
+    SectionData:     576F726C64210048656C6C6F2C00
+symbols:
+  - Name:            .text
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    NumberOfAuxSymbols: 1
+    AuxiliaryData:   3C0000000300000000000000010000000000
+  - Name:            .data
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    NumberOfAuxSymbols: 1
+    AuxiliaryData:   0E0000000000000000000000020000000000
+  - Name:            _start
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+...

lld/test/pecoff/alignment.test

@@ -0,0 +1,6 @@
+# RUN: yaml2obj %p/Inputs/alignment.obj.yaml > %t.obj
+#
+# RUN: lld -flavor link /out:%t1 /subsystem:console /force /entry:start \
+# RUN:   -- %t.obj && llvm-readobj -sections %t1 | FileCheck %s
+
+CHECK: VirtualSize: 0x1001