[lld] r188025 - [PECOFF] Support COMDAT section that contains mergeable atoms.
Rui Ueyama
ruiu at google.com
Thu Aug 8 16:31:50 PDT 2013
Author: ruiu
Date: Thu Aug 8 18:31:50 2013
New Revision: 188025
URL: http://llvm.org/viewvc/llvm-project?rev=188025&view=rev
Log:
[PECOFF] Support COMDAT section that contains mergeable atoms.
The COMDAT section is a section with a special attribute to tell the linker
whether the symbols in the section are allowed to be merged or not. This patch
add a function to interpret the COMDAT data and set "merge" attribute to the
atoms accordingly.
LLD supports multiple policies to merge atoms; atoms can be merged by name or
by content. COFF supports them, and in addition to that, it supports
choose-the-largest-atom policy, which LLD currently does not support. I simply
mapped it to merge-by-name attribute for now, but we eventually have to support
that policy in the core linker.
Added:
lld/trunk/test/pecoff/Inputs/comdat.obj.yaml
lld/trunk/test/pecoff/comdat.test
Modified:
lld/trunk/lib/ReaderWriter/PECOFF/Atoms.h
lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
Modified: lld/trunk/lib/ReaderWriter/PECOFF/Atoms.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/Atoms.h?rev=188025&r1=188024&r2=188025&view=diff
==============================================================================
--- lld/trunk/lib/ReaderWriter/PECOFF/Atoms.h (original)
+++ lld/trunk/lib/ReaderWriter/PECOFF/Atoms.h Thu Aug 8 18:31:50 2013
@@ -175,15 +175,17 @@ class COFFDefinedAtom : public COFFDefin
public:
COFFDefinedAtom(const File &file, StringRef name, StringRef sectionName,
Scope scope, ContentType type, ContentPermissions perms,
- ArrayRef<uint8_t> data, uint64_t ordinal)
+ Merge merge, ArrayRef<uint8_t> data, uint64_t ordinal)
: COFFDefinedFileAtom(file, name, sectionName, scope, type, perms,
ordinal),
- _dataref(data) {}
+ _merge(merge), _dataref(data) {}
+ virtual Merge merge() const { return _merge; }
virtual uint64_t size() const { return _dataref.size(); }
virtual ArrayRef<uint8_t> rawContent() const { return _dataref; }
private:
+ Merge _merge;
ArrayRef<uint8_t> _dataref;
};
Modified: lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp?rev=188025&r1=188024&r2=188025&view=diff
==============================================================================
--- lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp (original)
+++ lld/trunk/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp Thu Aug 8 18:31:50 2013
@@ -38,6 +38,7 @@ using lld::coff::COFFDefinedAtom;
using lld::coff::COFFDefinedFileAtom;
using lld::coff::COFFReference;
using lld::coff::COFFUndefinedAtom;
+using llvm::object::coff_aux_section_definition;
using llvm::object::coff_relocation;
using llvm::object::coff_section;
using llvm::object::coff_symbol;
@@ -46,6 +47,7 @@ using namespace lld;
namespace {
+// Converts the COFF symbol attribute to the LLD's atom attribute.
Atom::Scope getScope(const coff_symbol *symbol) {
switch (symbol->StorageClass) {
case llvm::COFF::IMAGE_SYM_CLASS_EXTERNAL:
@@ -79,6 +81,16 @@ DefinedAtom::ContentPermissions getPermi
return DefinedAtom::perm___;
}
+DefinedAtom::Merge getMerge(const coff_aux_section_definition *auxsym) {
+ switch (auxsym->Selection) {
+ case llvm::COFF::IMAGE_COMDAT_SELECT_NODUPLICATES:
+ return DefinedAtom::mergeNo;
+ default:
+ // FIXME: COFF supports more mergable symbol attributes.
+ return DefinedAtom::mergeAsWeakAndAddressUsed;
+ }
+}
+
class FileCOFF : public File {
private:
typedef vector<const coff_symbol *> SymbolVectorT;
@@ -201,6 +213,13 @@ private:
/// we need to know the adjacent symbols.
error_code createDefinedSymbols(const SymbolVectorT &symbols,
vector<const DefinedAtom *> &result) {
+ // A defined atom can be merged if its section attribute allows its contents
+ // to be merged. In COFF, it's not very easy to get the section attribute
+ // for the symbol, so scan all sections in advance and cache the attributes
+ // for later use.
+ if (error_code ec = cacheSectionAttributes())
+ return ec;
+
// Filter non-defined atoms, and group defined atoms by its section.
SectionToSymbolsT definedSymbols;
for (const coff_symbol *sym : symbols) {
@@ -223,6 +242,22 @@ private:
sym->SectionNumber == llvm::COFF::IMAGE_SYM_UNDEFINED)
continue;
+ const coff_section *sec;
+ if (error_code ec = _obj->getSection(sym->SectionNumber, sec))
+ return ec;
+ assert(sec && "SectionIndex > 0, Sec must be non-null!");
+
+ // SKip if it's a section symbol for a COMDAT section. A section symbol
+ // has the name of the section and value 0. A translation unit may contain
+ // multiple COMDAT sections whose section name are the same. We don't want
+ // to make atoms for them as they would become duplicate symbols.
+ StringRef sectionName;
+ if (error_code ec = _obj->getSectionName(sec, sectionName))
+ return ec;
+ if (_symbolName[sym] == sectionName && sym->Value == 0 &&
+ _merge[sec] != DefinedAtom::mergeNo)
+ continue;
+
uint8_t sc = sym->StorageClass;
if (sc != llvm::COFF::IMAGE_SYM_CLASS_EXTERNAL &&
sc != llvm::COFF::IMAGE_SYM_CLASS_STATIC &&
@@ -233,10 +268,6 @@ private:
return llvm::object::object_error::parse_failed;
}
- const coff_section *sec;
- if (error_code ec = _obj->getSection(sym->SectionNumber, sec))
- return ec;
- assert(sec && "SectionIndex > 0, Sec must be non-null!");
definedSymbols[sec].push_back(sym);
}
@@ -247,6 +278,55 @@ private:
return error_code::success();
}
+ // Cache the COMDAT attributes, which indicate whether the symbols in the
+ // section can be merged or not.
+ error_code cacheSectionAttributes() {
+ const llvm::object::coff_file_header *header = nullptr;
+ if (error_code ec = _obj->getHeader(header))
+ return ec;
+
+ // The COMDAT section attribute is not an attribute of coff_section, but is
+ // stored in the auxiliary symbol for the first symbol referring a COMDAT
+ // section. It feels to me that it's unnecessarily complicated, but this is
+ // how COFF works.
+ for (uint32_t i = 0, e = header->NumberOfSymbols; i != e; ++i) {
+ const coff_symbol *sym;
+ if (error_code ec = _obj->getSymbol(i, sym))
+ return ec;
+ if (sym->SectionNumber == llvm::COFF::IMAGE_SYM_ABSOLUTE ||
+ sym->SectionNumber == llvm::COFF::IMAGE_SYM_UNDEFINED)
+ continue;
+
+ const coff_section *sec;
+ if (error_code ec = _obj->getSection(sym->SectionNumber, sec))
+ return ec;
+
+ if (_merge.count(sec))
+ continue;
+ if (!(sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_COMDAT))
+ continue;
+
+ if (sym->NumberOfAuxSymbols == 0)
+ return llvm::object::object_error::parse_failed;
+ const coff_aux_section_definition *aux = nullptr;
+ if (error_code ec = _obj->getAuxSymbol(i + 1, aux))
+ return ec;
+
+ _merge[sec] = getMerge(aux);
+ }
+
+ // The sections that does not have auxiliary symbol are regular sections, in
+ // which symbols are not allowed to be merged.
+ error_code ec;
+ for (auto si = _obj->begin_sections(), se = _obj->end_sections(); si != se;
+ si.increment(ec)) {
+ const coff_section *sec = _obj->getCOFFSection(si);
+ if (!_merge.count(sec))
+ _merge[sec] = DefinedAtom::mergeNo;
+ }
+ return error_code::success();
+ }
+
/// Atomize \p symbols and append the results to \p atoms. The symbols are
/// assumed to have been defined in the \p section.
error_code
@@ -310,7 +390,7 @@ private:
ArrayRef<uint8_t> data(secData.data(), secData.size());
auto *atom = new (_alloc) COFFDefinedAtom(
*this, "", sectionName, Atom::scopeTranslationUnit, type, perms,
- data, 0);
+ _merge[section], data, 0);
atoms.push_back(atom);
_definedAtomLocations[section][0] = atom;
return error_code::success();
@@ -323,7 +403,7 @@ private:
ArrayRef<uint8_t> data(secData.data(), size);
auto *atom = new (_alloc) COFFDefinedAtom(
*this, "", sectionName, Atom::scopeTranslationUnit, type, perms,
- data, ++ordinal);
+ _merge[section], data, ++ordinal);
atoms.push_back(atom);
_definedAtomLocations[section][0] = atom;
}
@@ -337,7 +417,7 @@ private:
ArrayRef<uint8_t> data(start, end);
auto *atom = new (_alloc) COFFDefinedAtom(
*this, _symbolName[*si], sectionName, getScope(*si), type, perms,
- data, ++ordinal);
+ _merge[section], data, ++ordinal);
atoms.push_back(atom);
_symbolAtom[*si] = atom;
_definedAtomLocations[section][(*si)->Value] = atom;
@@ -519,6 +599,9 @@ private:
// A map from section to its atoms.
std::map<const coff_section *, vector<COFFDefinedFileAtom *>> _sectionAtoms;
+ // A map to get whether the section allows its contents to be merged or not.
+ std::map<const coff_section *, DefinedAtom::Merge> _merge;
+
// A sorted map to find an atom from a section and an offset within
// the section.
std::map<const coff_section *,
Added: lld/trunk/test/pecoff/Inputs/comdat.obj.yaml
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/Inputs/comdat.obj.yaml?rev=188025&view=auto
==============================================================================
--- lld/trunk/test/pecoff/Inputs/comdat.obj.yaml (added)
+++ lld/trunk/test/pecoff/Inputs/comdat.obj.yaml Thu Aug 8 18:31:50 2013
@@ -0,0 +1,43 @@
+---
+header:
+ Machine: IMAGE_FILE_MACHINE_I386
+ Characteristics: [ ]
+sections:
+ - Name: .text
+ Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+ Alignment: 16
+ SectionData: 558BEC33C05DC3
+ - Name: .text
+ Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+ Alignment: 16
+ SectionData: 558BEC33C05DC3
+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: 0700000000000000C979F796000002000000
+ - Name: .text
+ Value: 0
+ SectionNumber: 2
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_NULL
+ StorageClass: IMAGE_SYM_CLASS_STATIC
+ NumberOfAuxSymbols: 1
+ AuxiliaryData: 0700000000000000C979F796000002000000
+ - Name: "?inlinefn1@@YAHXZ"
+ Value: 0
+ SectionNumber: 1
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_FUNCTION
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+ - Name: "?inlinefn2@@YAHXZ"
+ Value: 0
+ SectionNumber: 2
+ SimpleType: IMAGE_SYM_TYPE_NULL
+ ComplexType: IMAGE_SYM_DTYPE_FUNCTION
+ StorageClass: IMAGE_SYM_CLASS_EXTERNAL
+...
Added: lld/trunk/test/pecoff/comdat.test
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/pecoff/comdat.test?rev=188025&view=auto
==============================================================================
--- lld/trunk/test/pecoff/comdat.test (added)
+++ lld/trunk/test/pecoff/comdat.test Thu Aug 8 18:31:50 2013
@@ -0,0 +1,12 @@
+# RUN: yaml2obj %p/Inputs/comdat.obj.yaml > %t1.obj
+# RUN: yaml2obj %p/Inputs/comdat.obj.yaml > %t2.obj
+#
+# RUN: lld -flavor link /out:%t3.exe /subsystem:console /force \
+# RUN: -- %t1.obj %t2.obj 2>&1 > %t.log
+#
+# FileCheck complains if the input files is empty, so add a dummy line.
+# RUN: echo foo >> %t.log
+#
+# RUN: FileCheck %s < %t.log
+
+CHECK-NOT: duplicate symbol error
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