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[LLD] [COFF] Check the aux section definition size for IMAGE_COMDAT_SELECT_SAME_SIZE 

Binutils generated sections seem to be padded to a multiple of 16 bytes,
but the aux section definition contains the original, unpadded section
length.

The size check used for IMAGE_COMDAT_SELECT_SAME_SIZE previously
only checked the size of the section itself. When checking the
currently processed object file against the previously chosen
comdat section, we easily have access to the aux section definition
of the currently processed section, but we have to iterate over the
symbols of the previously selected object file to find the section
definition of the previously picked section. (We don't want to
inflate SectionChunk to carry more data, for something that is only
needed in corner cases.) Only do this when the mingw flag is set.

This fixes statically linking clang-built C++ object files against
libstdc++ built with GCC, if the object files contain e.g. typeinfo.

Differential Revision: https://reviews.llvm.org/D86659
This commit is contained in:
Martin Storsjö 2020-08-26 15:47:04 +03:00
parent e72403f96d
commit df8f3bf626
5 changed files with 107 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
lld/COFF/InputFiles.cpp
View File

@ -472,8 +472,23 @@ Symbol *ObjFile::createUndefined(COFFSymbolRef sym) {
return symtab->addUndefined(name, this, sym.isWeakExternal());
}
void ObjFile::handleComdatSelection(COFFSymbolRef sym, COMDATType &selection,
bool &prevailing, DefinedRegular *leader) {
static const coff_aux_section_definition *findSectionDef(COFFObjectFile *obj,
int32_t section) {
uint32_t numSymbols = obj->getNumberOfSymbols();
for (uint32_t i = 0; i < numSymbols; ++i) {
COFFSymbolRef sym = check(obj->getSymbol(i));
if (sym.getSectionNumber() != section)
continue;
if (const coff_aux_section_definition *def = sym.getSectionDefinition())
return def;
}
return nullptr;
}
void ObjFile::handleComdatSelection(
COFFSymbolRef sym, COMDATType &selection, bool &prevailing,
DefinedRegular *leader,
const llvm::object::coff_aux_section_definition *def) {
if (prevailing)
return;
// There's already an existing comdat for this symbol: `Leader`.
@ -540,8 +555,16 @@ void ObjFile::handleComdatSelection(COFFSymbolRef sym, COMDATType &selection,
break;
case IMAGE_COMDAT_SELECT_SAME_SIZE:
if (leaderChunk->getSize() != getSection(sym)->SizeOfRawData)
symtab->reportDuplicate(leader, this);
if (leaderChunk->getSize() != getSection(sym)->SizeOfRawData) {
if (!config->mingw) {
symtab->reportDuplicate(leader, this);
} else {
const coff_aux_section_definition *leaderDef = findSectionDef(
leaderChunk->file->getCOFFObj(), leaderChunk->getSectionNumber());
if (!leaderDef || leaderDef->Length != def->Length)
symtab->reportDuplicate(leader, this);
}
}
break;
case IMAGE_COMDAT_SELECT_EXACT_MATCH: {
@ -657,7 +680,7 @@ Optional<Symbol *> ObjFile::createDefined(
COMDATType selection = (COMDATType)def->Selection;
if (leader->isCOMDAT)
handleComdatSelection(sym, selection, prevailing, leader);
handleComdatSelection(sym, selection, prevailing, leader, def);
if (prevailing) {
SectionChunk *c = readSection(sectionNumber, def, getName());

7
lld/COFF/InputFiles.h
View File

@ -255,9 +255,10 @@ private:
// match the existing symbol and its selection. If either old or new
// symbol have selection IMAGE_COMDAT_SELECT_LARGEST, Sym might replace
// the existing leader. In that case, Prevailing is set to true.
void handleComdatSelection(COFFSymbolRef sym,
llvm::COFF::COMDATType &selection,
bool &prevailing, DefinedRegular *leader);
void
handleComdatSelection(COFFSymbolRef sym, llvm::COFF::COMDATType &selection,
bool &prevailing, DefinedRegular *leader,
const llvm::object::coff_aux_section_definition *def);
llvm::Optional<Symbol *>
createDefined(COFFSymbolRef sym,

30
lld/test/COFF/Inputs/comdat-binutils.yaml Normal file
View File

@ -0,0 +1,30 @@
--- !COFF
header:
Machine: IMAGE_FILE_MACHINE_AMD64
Characteristics: [ IMAGE_FILE_RELOCS_STRIPPED, IMAGE_FILE_LINE_NUMS_STRIPPED ]
sections:
- Name: '.rdata$mysymbol'
Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_READ ]
Alignment: 16
SectionData: 2A000000000000000000000000000000
symbols:
- Name: '.rdata$mysymbol'
Value: 0
SectionNumber: 1
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_STATIC
SectionDefinition:
Length: 1
NumberOfRelocations: 0
NumberOfLinenumbers: 0
CheckSum: 0
Number: 0
Selection: IMAGE_COMDAT_SELECT_SAME_SIZE
- Name: mysymbol
Value: 0
SectionNumber: 1
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_EXTERNAL
...

30
lld/test/COFF/Inputs/comdat-llvm.yaml Normal file
View File

@ -0,0 +1,30 @@
--- !COFF
header:
Machine: IMAGE_FILE_MACHINE_AMD64
Characteristics: [ ]
sections:
- Name: '.rdata$mysymbol'
Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_READ ]
Alignment: 1
SectionData: 2A
symbols:
- Name: '.rdata$mysymbol'
Value: 0
SectionNumber: 1
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_STATIC
SectionDefinition:
Length: 1
NumberOfRelocations: 0
NumberOfLinenumbers: 0
CheckSum: 3686517206
Number: 1
Selection: IMAGE_COMDAT_SELECT_SAME_SIZE
- Name: mysymbol
Value: 0
SectionNumber: 1
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_EXTERNAL
...

15
lld/test/COFF/comdat-gcc-compatibility-size.test Normal file
View File

@ -0,0 +1,15 @@
# RUN: yaml2obj %p/Inputs/comdat-llvm.yaml > %t.llvm.o
# RUN: yaml2obj %p/Inputs/comdat-binutils.yaml > %t.binutils.o
# RUN: lld-link -lldmingw -noentry -dll %t.llvm.o %t.binutils.o -out:%t.dll
# RUN: lld-link -lldmingw -noentry -dll %t.binutils.o %t.llvm.o -out:%t.dll
# RUN: not lld-link -noentry -dll %t.llvm.o %t.binutils.o -out:%t.dll
# RUN: not lld-link -noentry -dll %t.binutils.o %t.llvm.o -out:%t.dll
# The test object files have been generated by assembling the following
# snippet using binutils and llvm.
# .section .rdata$mysymbol, "dr"
# .linkonce same_size
# .globl mysymbol
#mysymbol:
# .byte 42