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Reland [LLD] [COFF] Fix linking MSVC generated implib header objects (#123916)

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ecb5ea6a26 tried to fix cases when LLD
links what seems to be import library header objects from MSVC. However,
the fix seems incorrect; the review at https://reviews.llvm.org/D133627
concluded that if this (treating this kind of symbol as a common symbol)
is what link.exe does, it's fine.

However, this is most probably not what link.exe does. The symbol
mentioned in the commit message of
ecb5ea6a26 would be a common symbol with a
size of around 3 GB; this is not what might have been intended.

That commit tried to avoid running into the error ".idata$4 should not
refer to special section 0"; that issue is fixed for a similar style of
section symbols in 4a4a8a1476.

Therefore, revert ecb5ea6a26 and extend
the fix from 4a4a8a1476 to also work for
the section symbols in MSVC generated import libraries.

The main detail about them, is that for symbols of type
IMAGE_SYM_CLASS_SECTION, the Value field is not an offset, but it is an
optional set of flags, corresponding to the Characteristics of the
section header (although it may be empty).

This is a reland of a previous version of this commit, earlier merged in
9457418e66 / #122811. The previous version
failed tests when run with address sanitizer. The issue was that the
synthesized coff_symbol_generic object actually will be used to access a
full coff_symbol16 or coff_symbol32 struct, see
DefinedCOFF::getCOFFSymbol. Therefore, we need to make a copy of the
full size of either of them.
This commit is contained in:
Martin Storsjö
2025-01-23 09:15:47 +02:00
committed by GitHub
parent 3fb8c5b431
commit 8eb99bbe6e
4 changed files with 46 additions and 37 deletions
Download Patch File Download Diff File Expand all files Collapse all files

43
lld/COFF/InputFiles.cpp
View File

@@ -105,6 +105,18 @@ static bool ignoredSymbolName(StringRef name) {
return name == "@feat.00" || name == "@comp.id";
}
static coff_symbol_generic *cloneSymbol(COFFSymbolRef sym) {
if (sym.isBigObj()) {
auto *copy = make<coff_symbol32>(
*reinterpret_cast<const coff_symbol32 *>(sym.getRawPtr()));
return reinterpret_cast<coff_symbol_generic *>(copy);
} else {
auto *copy = make<coff_symbol16>(
*reinterpret_cast<const coff_symbol16 *>(sym.getRawPtr()));
return reinterpret_cast<coff_symbol_generic *>(copy);
}
}
ArchiveFile::ArchiveFile(COFFLinkerContext &ctx, MemoryBufferRef m)
: InputFile(ctx.symtab, ArchiveKind, m) {}
@@ -458,9 +470,16 @@ Symbol *ObjFile::createRegular(COFFSymbolRef sym) {
return nullptr;
return symtab.addUndefined(name, this, false);
}
if (sc)
if (sc) {
const coff_symbol_generic *symGen = sym.getGeneric();
if (sym.isSection()) {
auto *customSymGen = cloneSymbol(sym);
customSymGen->Value = 0;
symGen = customSymGen;
}
return make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,
/*IsExternal*/ false, sym.getGeneric(), sc);
/*IsExternal*/ false, symGen, sc);
}
return nullptr;
}
@@ -755,15 +774,23 @@ std::optional<Symbol *> ObjFile::createDefined(
memset(hdr, 0, sizeof(*hdr));
strncpy(hdr->Name, name.data(),
std::min(name.size(), (size_t)COFF::NameSize));
// We have no idea what characteristics should be assumed here; pick
// a default. This matches what is used for .idata sections in the regular
// object files in import libraries.
hdr->Characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ |
IMAGE_SCN_MEM_WRITE | IMAGE_SCN_ALIGN_4BYTES;
// The Value field in a section symbol may contain the characteristics,
// or it may be zero, where we make something up (that matches what is
// used in .idata sections in the regular object files in import libraries).
if (sym.getValue())
hdr->Characteristics = sym.getValue() | IMAGE_SCN_ALIGN_4BYTES;
else
hdr->Characteristics = IMAGE_SCN_CNT_INITIALIZED_DATA |
IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE |
IMAGE_SCN_ALIGN_4BYTES;
auto *sc = make<SectionChunk>(this, hdr);
chunks.push_back(sc);
auto *symGen = cloneSymbol(sym);
// Ignore the Value offset of these symbols, as it may be a bitmask.
symGen->Value = 0;
return make<DefinedRegular>(this, /*name=*/"", /*isCOMDAT=*/false,
/*isExternal=*/false, sym.getGeneric(), sc);
/*isExternal=*/false, symGen, sc);
}
if (llvm::COFF::isReservedSectionNumber(sectionNumber))

13
lld/test/COFF/empty-section-decl.yaml
View File

@@ -6,7 +6,7 @@
# RUN: FileCheck %s --check-prefix=MAP < %t.map
# CHECK: Contents of section .itest:
# CHECK-NEXT: 180001000 0c100080 01000000 00000000 01000000
# CHECK-NEXT: 180001000 0c100000 0c100000 00000000 01000000
# MAP: 00001000 0000000a 4 {{.*}}:(.itest$2)
# MAP: 00001000 00000000 0 .itest$2
@@ -28,7 +28,10 @@ sections:
Relocations:
- VirtualAddress: 0
SymbolName: '.itest$4'
Type: IMAGE_REL_AMD64_ADDR64
Type: IMAGE_REL_AMD64_ADDR32NB
- VirtualAddress: 4
SymbolName: '.itest$6'
Type: IMAGE_REL_AMD64_ADDR32NB
- Name: '.itest$6'
Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ, IMAGE_SCN_MEM_WRITE ]
Alignment: 2
@@ -42,13 +45,13 @@ symbols:
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_SECTION
- Name: '.itest$6'
Value: 0
Value: 3221225536
SectionNumber: 2
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_STATIC
StorageClass: IMAGE_SYM_CLASS_SECTION
- Name: '.itest$4'
Value: 0
Value: 3221225536
SectionNumber: 0
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL

7
llvm/include/llvm/Object/COFF.h
View File

@@ -383,8 +383,8 @@ public:
}
bool isCommon() const {
return (isExternal() || isSection()) &&
getSectionNumber() == COFF::IMAGE_SYM_UNDEFINED && getValue() != 0;
return isExternal() && getSectionNumber() == COFF::IMAGE_SYM_UNDEFINED &&
getValue() != 0;
}
bool isUndefined() const {
@@ -393,8 +393,7 @@ public:
}
bool isEmptySectionDeclaration() const {
return isSection() && getSectionNumber() == COFF::IMAGE_SYM_UNDEFINED &&
getValue() == 0;
return isSection() && getSectionNumber() == COFF::IMAGE_SYM_UNDEFINED;
}
bool isWeakExternal() const {

20
llvm/test/Object/coff-sec-sym.test
View File

@@ -1,20 +0,0 @@
# Check that section symbol (IMAGE_SYM_CLASS_SECTION) is listed as common symbol.
# RUN: yaml2obj %s -o %t.obj
# RUN: llvm-nm %t.obj | FileCheck %s
# CHECK: 00000001 C foo
--- !COFF
header:
Machine: IMAGE_FILE_MACHINE_AMD64
Characteristics: [ ]
sections:
symbols:
- Name: foo
Value: 1
SectionNumber: 0
SimpleType: IMAGE_SYM_TYPE_NULL
ComplexType: IMAGE_SYM_DTYPE_NULL
StorageClass: IMAGE_SYM_CLASS_SECTION
...