[LLD][COFF] Handle 'label' symbols when they point to a COMDAT section

[aganea]

Summary

This fixes an issue where OBJs files containing a malformed .text$x section references label symbols (that is IMAGE_SYM_CLASS_LABEL) that live in a COMDAT .text$mn. This kind of OBJ files are generated when using binutils objcopy. A tentative reproducer can be found here in https://github.com/llvm/llvm-project/issues/62182. This patch already contains a test that covers the bug.

Fixes PR62182.

[compnerd]

lld/COFF/InputFiles.cpp

628

Interesting. I think that we should add a comment about this impacts identity and comparison. Does this change in definition have any impact on ICF? IIRC, we did have a minor difference between link and lld in that regard.

lld/COFF/InputFiles.h

267

Can we use a typedef for the std::vector<std::pair<DefinedRegular *, const llvm::object::coff_aux_section_definition *>>?

[rnk]

Here are some comments, I have to run, so it's not complete, but hopefully still useful.

lld/COFF/InputFiles.cpp

388

This array is sparse, so we are adding a pointer for every input section, so this could be a performance sensitive change.

645

For my understanding, the problem is that the old code just returned the leader in this case, right? And you have solved the problem by synthesizing a new symbol to represent the label.

lld/test/COFF/Inputs/comdat-malformed-assoc-a.yaml

55

I see, .text$x is not comdat but .text$mn is. I think this test would be more readable in assembly. If you start with assembly output from clang, can you adjust the section directives to create the analogous situation?

[aganea]

Sorry I will answer to your comments a bit later. I was trying to understand the root issue, and I've managed to reproduce it locally.

The problem is not MSVC, but the way the packaging is done in firebase-sdk. Namely, it uses binutils objcopy which doesn't seem to understand COMDAT relationships (that is, IMAGE_COMDAT_SELECT_ASSOCIATIVE). Simply replacing by llvm-objcopy fixes the issue.

I'm also wondering if instead of this patch, we couldn't craft something simpler, an heuristic that "fixes" the section header and the section symbol. Usually they seems to come in a pair, .text$mn, .text$x or a trio if debug symbols are involved: .text$mn, .debug$S, .text$x. Opinions?

[compnerd]

I'm now less inclined to change the behaviour of lld to support this. It seems that given that this is a bug in objcopy, it should be something that could be mitigated by using llvm-objcopy, and fixing binutils to correctly comdat would be more useful. Adding additional context in the error message about the missing entries would help identify what is missing and hopefully allow the user to investigate and fix the issue? I also suspect that this is not going to be reproducible via MSVC alone (which was the original assumption), and there are other complications from using binutils to handle PE/COFF files in my experience.

[rnk]

In D157136#4583632, @aganea wrote:

I'm also wondering if instead of this patch, we couldn't craft something simpler, an heuristic that "fixes" the section header and the section symbol. Usually they seems to come in a pair, .text$mn, .text$x or a trio if debug symbols are involved: .text$mn, .debug$S, .text$x. Opinions?

I think there is prior art for doing this for mingw, we do some convoluted stuff to associate .text$_Z3foov / .pdata$_Z3foov / .xdata$_Z3foov together, but IIRC it's not good for performance.

I think for the moment I'm inclined to do nothing, unless this is really high priority for some user. It sounds like we can recommend using llvm-objcopy in place of binutils objcopy as a possible solution.

[aganea]

In D157136#4626520, @rnk wrote:

In D157136#4583632, @aganea wrote:

I'm also wondering if instead of this patch, we couldn't craft something simpler, an heuristic that "fixes" the section header and the section symbol. Usually they seems to come in a pair, .text$mn, .text$x or a trio if debug symbols are involved: .text$mn, .debug$S, .text$x. Opinions?

I think there is prior art for doing this for mingw, we do some convoluted stuff to associate .text$_Z3foov / .pdata$_Z3foov / .xdata$_Z3foov together, but IIRC it's not good for performance.

I think for the moment I'm inclined to do nothing, unless this is really high priority for some user. It sounds like we can recommend using llvm-objcopy in place of binutils objcopy as a possible solution.

I agree. One argument would be that link.exe supports this scenario without a warning. But since it only came up for a single user, and their root issue will be fixed eventually, it’s not worth adding a fix. We could however add an extra note when that error occurs, and suggest llvm-objcopy as a possible fix, do you think it’s worth it?

[rnk]

I think this kind of error ("relocation against symbol in discarded section") is really hard to debug, and probably deserves a whole page of documentation. I think the best option would be to emit a short link to online documentation describing the issue category in detail, something like https://lld.llvm.org/missingkeyfunction.html .

lld/COFF/InputFiles.h

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,
                         const llvm::object::coff_aux_section_definition *def);
 
-  std::optional<Symbol *>
-  createDefined(COFFSymbolRef sym,
-                std::vector<const llvm::object::coff_aux_section_definition *>
-                    &comdatDefs,
-                bool &prevailingComdat);
+  std::optional<Symbol *> createDefined(
+      COFFSymbolRef sym,
+      std::vector<std::pair<DefinedRegular *,
+                            const llvm::object::coff_aux_section_definition *>>
   Symbol *createRegular(COFFSymbolRef sym);
   Symbol *createUndefined(COFFSymbolRef sym);
 
   std::unique_ptr<COFFObjectFile> coffObj;
 
   // List of all chunks defined by this file. This includes both section
   // chunks and non-section chunks for common symbols.
   std::vector<Chunk *> chunks;

lld/COFF/InputFiles.cpp

void ObjFile::initializeSymbols() {
   uint32_t numSymbols = coffObj->getNumberOfSymbols();
   symbols.resize(numSymbols);
 
   SmallVector<std::pair<Symbol *, uint32_t>, 8> weakAliases;
   std::vector<uint32_t> pendingIndexes;
   pendingIndexes.reserve(numSymbols);
 
   DenseMap<StringRef, uint32_t> prevailingSectionMap;
-  std::vector<const coff_aux_section_definition *> comdatDefs(
-      coffObj->getNumberOfSections() + 1);
+  std::vector<std::pair<DefinedRegular *, const coff_aux_section_definition *>>
+      comdatDefs(coffObj->getNumberOfSections() + 1);
 
   for (uint32_t i = 0; i < numSymbols; ++i) {
     COFFSymbolRef coffSym = check(coffObj->getSymbol(i));
     bool prevailingComdat;
     if (coffSym.isUndefined()) {
       symbols[i] = createUndefined(coffSym);
     } else if (coffSym.isWeakExternal()) {
       symbols[i] = createUndefined(coffSym);
void ObjFile::handleComdatSelection(
 
   case IMAGE_COMDAT_SELECT_NEWEST:
     llvm_unreachable("should have been rejected earlier");
   }
 }
 
 std::optional<Symbol *> ObjFile::createDefined(
     COFFSymbolRef sym,
-    std::vector<const coff_aux_section_definition *> &comdatDefs,
+    std::vector<std::pair<DefinedRegular *,
+                          const coff_aux_section_definition *>> &comdatDefs,
     bool &prevailing) {
   prevailing = false;
   auto getName = [&]() { return check(coffObj->getSymbolName(sym)); };
 
   if (sym.isCommon()) {
     auto *c = make<CommonChunk>(sym);
     chunks.push_back(c);
     return ctx.symtab.addCommon(this, getName(), sym.getValue(),
if (llvm::COFF::isReservedSectionNumber(sectionNumber))
     fatal(toString(this) + ": " + getName() +
           " should not refer to special section " + Twine(sectionNumber));
 
   if ((uint32_t)sectionNumber >= sparseChunks.size())
     fatal(toString(this) + ": " + getName() +
           " should not refer to non-existent section " + Twine(sectionNumber));
 
   // Comdat handling.
-  // A comdat symbol consists of two symbol table entries.
+  // A comdat symbol consists of two symbol table entries, and a number of
+  // optional 'label' symbols.
   // The first symbol entry has the name of the section (e.g. .text), fixed
   // values for the other fields, and one auxiliary record.
   // The second symbol entry has the name of the comdat symbol, called the
   // "comdat leader".
   // When this function is called for the first symbol entry of a comdat,
   // it sets comdatDefs and returns std::nullopt, and when it's called for the
-  // second symbol entry it reads comdatDefs and then sets it back to nullptr.
+  // second symbol entry it reads comdatDefs.
+  // Any optional label symbols might come after in the symbol table.
 
+  DefinedRegular *leader{};
+  const coff_aux_section_definition *def{};
+  std::tie(leader, def) = comdatDefs[sectionNumber];
+  if (def) {
+    if (leader) {
+      // The leader symbol has already been resolved at this point. We redirect
+      // the label to point to the leader' section.
+      if (sym.isLabel()) {
+        return make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,
+                                    /*IsExternal*/ false, sym.getGeneric(),
+                                    leader->getChunk());
+      }
+    } else {
       // Handle comdat leader.
-  if (const coff_aux_section_definition *def = comdatDefs[sectionNumber]) {
-    comdatDefs[sectionNumber] = nullptr;
-    DefinedRegular *leader;
-
       if (sym.isExternal()) {
         std::tie(leader, prevailing) =
             ctx.symtab.addComdat(this, getName(), sym.getGeneric());
       } else {
         leader = make<DefinedRegular>(this, /*Name*/ "", /*IsCOMDAT*/ false,
                                       /*IsExternal*/ false, sym.getGeneric());
         prevailing = true;
       }
 
       if (def->Selection < (int)IMAGE_COMDAT_SELECT_NODUPLICATES ||
           // Intentionally ends at IMAGE_COMDAT_SELECT_LARGEST: link.exe
           // doesn't understand IMAGE_COMDAT_SELECT_NEWEST either.
           def->Selection > (int)IMAGE_COMDAT_SELECT_LARGEST) {
         fatal("unknown comdat type " + std::to_string((int)def->Selection) +
               " for " + getName() + " in " + toString(this));
       }
       COMDATType selection = (COMDATType)def->Selection;
 
       if (leader->isCOMDAT)
         handleComdatSelection(sym, selection, prevailing, leader, def);
 
       if (prevailing) {
         SectionChunk *c = readSection(sectionNumber, def, getName());
         sparseChunks[sectionNumber] = c;
         c->sym = cast<DefinedRegular>(leader);
         c->selection = selection;
         cast<DefinedRegular>(leader)->data = &c->repl;
       } else {
         sparseChunks[sectionNumber] = nullptr;
       }
+      comdatDefs[sectionNumber] = {leader, def};
       return leader;
     }
+  }
 
   // Prepare to handle the comdat leader symbol by setting the section's
   // ComdatDefs pointer if we encounter a non-associative comdat.
   if (sparseChunks[sectionNumber] == pendingComdat) {
     if (const coff_aux_section_definition *def = sym.getSectionDefinition()) {
       if (def->Selection != IMAGE_COMDAT_SELECT_ASSOCIATIVE)
-        comdatDefs[sectionNumber] = def;
+        comdatDefs[sectionNumber] = {/*leader=*/nullptr, def};
     }
     return std::nullopt;
   }
 
   return createRegular(sym);
 }
 
 MachineTypes ObjFile::getMachineType() {

lld/test/COFF/Inputs/comdat-malformed-assoc-a.yaml

+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4883EC2833C9E8000000004883C428C3
+    Relocations:
+      - VirtualAddress:  7
+        SymbolName:      '?func@@YAXPEAH@Z'
+        Type:            IMAGE_REL_AMD64_REL32
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     48894C24084883EC28488B442430C70000000000EB004883C428C3
+  - Name:            '.text$x'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4889542410554883EC20488BEA33D233C9E80000000090488D05000000004883C4205DC3CC
+    Relocations:
+      - VirtualAddress:  18
+        SymbolName:      _CxxThrowException
+        Type:            IMAGE_REL_AMD64_REL32
+      - VirtualAddress:  26
+        SymbolName:      '$LN7'
+        Type:            IMAGE_REL_AMD64_REL32
+symbols:
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          16
+      NumberOfRelocations: 1
+      NumberOfLinenumbers: 0
+      CheckSum:        221128940
+      Number:          0
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          27
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        928271883
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            '.text$x'
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          37
+      NumberOfRelocations: 2
+      NumberOfLinenumbers: 0
+      CheckSum:        39674339
+      Number:          0
+  - Name:            '?func@@YAXPEAH@Z'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '?a@@YAXXZ'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '?catch$0@?0??func@@YAXPEAH@Z@4HA'
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            _CxxThrowException
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            __CxxFrameHandler4
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '$LN7'
+    Value:           22
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            '$LN8'
+    Value:           27
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            '__catch$?func@@YAXPEAH@Z$0'
+    Value:           13
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            '$LN10'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            '$LN3'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+...

lld/test/COFF/Inputs/comdat-malformed-assoc-b.yaml

+--- !COFF
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [  ]
+sections:
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4883EC2833C9E8000000004883C428C3
+    Relocations:
+      - VirtualAddress:  7
+        SymbolName:      '?func@@YAXPEAH@Z'
+        Type:            IMAGE_REL_AMD64_REL32
+  - Name:            '.text$mn'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_LNK_COMDAT, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     48894C24084883EC28488B442430C70000000000EB004883C428C3
+  - Name:            '.text$x'
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    Alignment:       16
+    SectionData:     4889542410554883EC20488BEA33D233C9E80000000090488D05000000004883C4205DC3CC
+    Relocations:
+      - VirtualAddress:  18
+        SymbolName:      _CxxThrowException
+        Type:            IMAGE_REL_AMD64_REL32
+      - VirtualAddress:  26
+        SymbolName:      '$LN7'
+        Type:            IMAGE_REL_AMD64_REL32
+symbols:
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          16
+      NumberOfRelocations: 1
+      NumberOfLinenumbers: 0
+      CheckSum:        221128940
+      Number:          0
+  - Name:            '.text$mn'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          27
+      NumberOfRelocations: 0
+      NumberOfLinenumbers: 0
+      CheckSum:        928271883
+      Number:          0
+      Selection:       IMAGE_COMDAT_SELECT_ANY
+  - Name:            '.text$x'
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+    SectionDefinition:
+      Length:          37
+      NumberOfRelocations: 2
+      NumberOfLinenumbers: 0
+      CheckSum:        39674339
+      Number:          0
+  - Name:            '?func@@YAXPEAH@Z'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '?b@@YAXXZ'
+    Value:           0
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '?catch$0@?0??func@@YAXPEAH@Z@4HA'
+    Value:           0
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            _CxxThrowException
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            __CxxFrameHandler4
+    Value:           0
+    SectionNumber:   0
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+  - Name:            '$LN7'
+    Value:           22
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            '$LN8'
+    Value:           27
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            '__catch$?func@@YAXPEAH@Z$0'
+    Value:           13
+    SectionNumber:   3
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_FUNCTION
+    StorageClass:    IMAGE_SYM_CLASS_STATIC
+  - Name:            '$LN10'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+  - Name:            '$LN3'
+    Value:           0
+    SectionNumber:   2
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_LABEL
+...

lld/test/COFF/comdat-selection.s

 # LARGESTDISCARD: Contents of section .text:
 # LARGESTDISCARD:   180001000 01000000 ....
 
 
 # These cases are accepted by link.exe but not by lld-link.
 # RUN: not lld-link /verbose /dll /noentry /nodefaultlib %t.largest.obj %t.one_only.obj 2>&1 | FileCheck --check-prefix=LARGESTONE %s
 # LARGESTONE: lld-link: conflicting comdat type for symbol: 6 in
 # LARGESTONE: lld-link: error: duplicate symbol: symbol
+
+
+# Check a peculiar case where the .text$mn is a COMDAT but not the associated .text$x.
+# This is properly handled by link.exe, but it really looks like a bug in MSVC.
+# See PR62182.
+# RUN: yaml2obj %p/Inputs/comdat-malformed-assoc-a.yaml -o %t.a.obj
+# RUN: yaml2obj %p/Inputs/comdat-malformed-assoc-b.yaml -o %t.b.obj
+# RUN: lld-link %t.a.obj %t.b.obj /entry:a /subsystem:console /force:unresolved 2>&1 | FileCheck --check-prefix=MISSING-ASSOC %s
+# MISSING-ASSOC-NOT: error: relocation against symbol in discarded section:

llvm/include/llvm/Object/COFF.h

public:
   bool isAbsolute() const {
     return getSectionNumber() == -1;
   }
 
   bool isExternal() const {
     return getStorageClass() == COFF::IMAGE_SYM_CLASS_EXTERNAL;
   }
 
+  bool isLabel() const {
+    return getStorageClass() == COFF::IMAGE_SYM_CLASS_LABEL;
+  }
+
   bool isCommon() const {
     return (isExternal() || isSection()) &&
            getSectionNumber() == COFF::IMAGE_SYM_UNDEFINED && getValue() != 0;
   }
 
   bool isUndefined() const {
     return isExternal() && getSectionNumber() == COFF::IMAGE_SYM_UNDEFINED &&
            getValue() == 0;