kindLayoutBefore = 3,
// kindGroupChild is treated as a bidirected edge too.
kindGroupChild = 4,
+ // kindAssociate prevents a referenced atom from being dead-stripped.
+ kindAssociate = 5,
};
// A value to be added to the value of a target
uint64_t ordinal() const override { return _ordinal; }
Alignment alignment() const override { return _alignment; }
+ void associate(COFFDefinedFileAtom *other) {
+ auto *r = new COFFReference(other, 0, Reference::kindAssociate,
+ Reference::KindNamespace::all,
+ Reference::KindArch::all);
+ addReference(std::unique_ptr<COFFReference>(r));
+ }
+
private:
StringRef _sectionName;
Scope _scope;
// A map to get whether the section allows its contents to be merged or not.
std::map<const coff_section *, DefinedAtom::Merge> _merge;
+ // COMDAT associative sections
+ std::map<const coff_section *, std::set<const coff_section *>> _association;
+
// A sorted map to find an atom from a section and an offset within
// the section.
std::map<const coff_section *,
// section. It feels to me that it's unnecessarily complicated, but this is
// how COFF works.
for (auto i : _auxSymbol) {
+ // Read a section from the file
const coff_symbol *sym = i.first;
if (sym->SectionNumber == llvm::COFF::IMAGE_SYM_ABSOLUTE ||
sym->SectionNumber == llvm::COFF::IMAGE_SYM_UNDEFINED)
const coff_section *sec;
if (error_code ec = _obj->getSection(sym->SectionNumber, sec))
return ec;
+ const coff_aux_section_definition *aux =
+ reinterpret_cast<const coff_aux_section_definition *>(i.second);
- if (_merge.count(sec))
- continue;
- if (!(sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_COMDAT))
- continue;
-
- _comdatSections.insert(sec);
+ if (sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_COMDAT) {
+ // Read aux symbol data.
+ _comdatSections.insert(sec);
+ _merge[sec] = getMerge(aux);
+ }
- if (sym->NumberOfAuxSymbols == 0)
- return llvm::object::object_error::parse_failed;
- const coff_aux_section_definition *aux =
- reinterpret_cast<const coff_aux_section_definition *>(i.second);
- _merge[sec] = getMerge(aux);
+ // Handle associative sections.
+ if (aux->Selection == llvm::COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
+ const coff_section *parent;
+ if (error_code ec = _obj->getSection(aux->Number, parent))
+ return ec;
+ _association[parent].insert(sec);
+ }
}
// The sections that does not have auxiliary symbol are regular sections, in
definedAtoms.push_back(atom);
}
}
+
+ // A COMDAT section with SELECT_ASSOCIATIVE attribute refer to other
+ // section. They need to be linked to a binary or dead stripped as a group.
+ // Here We add a kindAssociate edge between them, so that if a target section
+ // is linked, the other is also linked.
+ //
+ // In a typical use case, parent is a comdat BSS section, and a child is a
+ // static initializer for the data.
+ for (auto i : _association) {
+ const coff_section *parent = i.first;
+ const std::set<const coff_section *> &childSections = i.second;
+ assert(_sectionAtoms[parent].size() > 0);
+
+ COFFDefinedFileAtom *p = _sectionAtoms[parent][0];
+ for (const coff_section *sec : childSections) {
+ if (_sectionAtoms.count(sec)) {
+ assert(_sectionAtoms[sec].size() > 0);
+ p->associate(_sectionAtoms[sec][0]);
+ }
+ }
+ }
+
return error_code();
}
{Reference::kindLayoutAfter, "layout-after"},
{Reference::kindLayoutBefore, "layout-before"},
{Reference::kindGroupChild, "group-child"},
+ {Reference::kindAssociate, "associate"},
LLD_KIND_STRING_END};
Registry::Registry() {
--- /dev/null
+---
+header:
+ Machine: IMAGE_FILE_MACHINE_I386
+ Characteristics: []
+sections:
+ - Name: .data
+ Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
+ Alignment: 4
+ SectionData: 00000000
+ - Name: '.CRT$XCU'
+ Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+ Alignment: 4
+ SectionData: 77777777
+symbols:
+ - Name: .data
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ SectionDefinition:
+ Length: 4
+ NumberOfRelocations: 0
+ NumberOfLinenumbers: 0
+ CheckSum: 0
+ Number: 0
+ Selection: IMAGE_COMDAT_SELECT_ANY
+ - Name: _var
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+ - Name: '.CRT$XCU'
+ Value: 0
+ SectionNumber: 2
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ SectionDefinition:
+ Length: 4
+ NumberOfRelocations: 0
+ NumberOfLinenumbers: 0
+ CheckSum: 0
+ Number: 1
+ Selection: IMAGE_COMDAT_SELECT_ASSOCIATIVE
+ - Name: _init
+ Value: 0
+ SectionNumber: 2
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+...
--- /dev/null
+---
+header:
+ Machine: IMAGE_FILE_MACHINE_I386
+ Characteristics: []
+sections:
+ - Name: .text
+ Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+ Alignment: 4
+ SectionData: 0000000000000000
+ Relocations:
+ - VirtualAddress: 4
+ SymbolName: _var
+ Type: IMAGE_REL_I386_DIR32
+symbols:
+ - Name: .text
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ - Name: _main
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+ - Name: _var
+ Value: 0
+ SectionNumber: 0
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+...
--- /dev/null
+# RUN: yaml2obj %p/Inputs/associative1.obj.yaml > %t1.obj
+# RUN: yaml2obj %p/Inputs/associative1.obj.yaml > %t2.obj
+# RUN: yaml2obj %p/Inputs/associative3.obj.yaml > %t3.obj
+#
+# RUN: lld -flavor link /machine:x86 /subsystem:console /entry:main \
+# RUN: /out:%t.exe -- %t1.obj %t2.obj %t3.obj
+# RUN: obj2yaml %t.exe | FileCheck %s
+
+CHECK: - Name: .CRT
+CHECK: SectionData: '77777777'