Index: test/tools/llvm-readobj/broken-group.test
===================================================================
--- test/tools/llvm-readobj/broken-group.test
+++ test/tools/llvm-readobj/broken-group.test
@@ -0,0 +1,41 @@
+broken-group.obj.elf-x86_64 contans 2 COMDAT groups and each one contains
+the same section foo. This is a result of bug in linker.
+Testcase shows that llvm-readobj reports error in that case.
+Linker used: LLD 6.0.0 (trunk 310596) (compatible with GNU linkers)
+Code:
+.section        .foo,"axG",@progbits,bar,comdat
+.section        .foo,"axG",@progbits,zed,comdat
+Invocation:
+ld.lld -r test.o -o out.lld
+
+RUN: llvm-readobj --elf-section-groups -elf-output-style=GNU \
+RUN:   %p/Inputs/broken-group.obj.elf-x86_64 | FileCheck %s -check-prefix=GNU
+GNU:      COMDAT group section [    2] `.group' [bar] contains 1 sections:
+GNU-NEXT:   [Index]    Name
+GNU-NEXT:   [    3]   .foo
+GNU:      COMDAT group section [    4] `.group' [zed] contains 1 sections:
+GNU-NEXT:   [Index]    Name
+GNU-NEXT:   Error: section [    3] in group section [    4] already in group section [    2]
+
+RUN: llvm-readobj --elf-section-groups \
+RUN:   %p/Inputs/broken-group.obj.elf-x86_64 | FileCheck %s -check-prefix=LLVM
+LLVM:      Groups {
+LLVM-NEXT:   Group {
+LLVM-NEXT:     Name: .group
+LLVM-NEXT:     Index: 2
+LLVM-NEXT:     Type: COMDAT
+LLVM-NEXT:     Signature: bar
+LLVM-NEXT:     Section(s) in group [
+LLVM-NEXT:       .foo (3)
+LLVM-NEXT:     ]
+LLVM-NEXT:   }
+LLVM-NEXT:   Group {
+LLVM-NEXT:     Name: .group
+LLVM-NEXT:     Index: 4
+LLVM-NEXT:     Type: COMDAT
+LLVM-NEXT:     Signature: zed
+LLVM-NEXT:     Section(s) in group [
+LLVM-NEXT:       Error: .foo (3) already in a group .group (2)
+LLVM-NEXT:     ]
+LLVM-NEXT:   }
+LLVM-NEXT: }
Index: tools/llvm-readobj/ELFDumper.cpp
===================================================================
--- tools/llvm-readobj/ELFDumper.cpp
+++ tools/llvm-readobj/ELFDumper.cpp
@@ -18,6 +18,7 @@
 #include "StackMapPrinter.h"
 #include "llvm-readobj.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/SmallString.h"
@@ -2444,6 +2445,7 @@
 template <class ELFT> void GNUStyle<ELFT>::printGroupSections(const ELFO *Obj) {
   uint32_t SectionIndex = 0;
   bool HasGroups = false;
+  DenseMap<uint32_t, uint32_t> SectionToGroup;
   for (const Elf_Shdr &Sec : unwrapOrError(Obj->sections())) {
     if (Sec.sh_type == ELF::SHT_GROUP) {
       HasGroups = true;
@@ -2459,7 +2461,15 @@
          << StrTable.data() + Signature->st_name << "] contains "
          << (Data.size() - 1) << " sections:\n"
          << "   [Index]    Name\n";
-      for (auto &Ndx : Data.slice(1)) {
+      for (Elf_Word Ndx : Data.slice(1)) {
+        auto It = SectionToGroup.insert({Ndx, SectionIndex});
+        if (!It.second) {
+          OS << "Error: section [" << format_decimal(Ndx, 5)
+             << "] in group section [" << format_decimal(SectionIndex, 5)
+             << "] already in group section ["
+             << format_decimal(It.first->second, 5) << "]";
+          continue;
+        }
         auto Sec = unwrapOrError(Obj->getSection(Ndx));
         const StringRef Name = unwrapOrError(Obj->getSectionName(Sec));
         OS << "   [" << format_decimal(Ndx, 5) << "]   " << Name
@@ -3491,6 +3501,7 @@
   DictScope Lists(W, "Groups");
   uint32_t SectionIndex = 0;
   bool HasGroups = false;
+  DenseMap<uint32_t, std::pair<StringRef, uint32_t>> SectionToGroup;
   for (const Elf_Shdr &Sec : unwrapOrError(Obj->sections())) {
     if (Sec.sh_type == ELF::SHT_GROUP) {
       HasGroups = true;
@@ -3501,8 +3512,8 @@
       auto Data = unwrapOrError(
           Obj->template getSectionContentsAsArray<Elf_Word>(&Sec));
       DictScope D(W, "Group");
-      StringRef Name = unwrapOrError(Obj->getSectionName(&Sec));
-      W.printNumber("Name", Name, Sec.sh_name);
+      StringRef GroupName = unwrapOrError(Obj->getSectionName(&Sec));
+      W.printNumber("Name", GroupName, Sec.sh_name);
       W.printNumber("Index", SectionIndex);
       W.printHex("Type", getGroupType(Data[0]), Data[0]);
       W.startLine() << "Signature: " << StrTable.data() + Sym->st_name << "\n";
@@ -3511,8 +3522,18 @@
         size_t Member = 1;
         while (Member < Data.size()) {
           auto Sec = unwrapOrError(Obj->getSection(Data[Member]));
-          const StringRef Name = unwrapOrError(Obj->getSectionName(Sec));
-          W.startLine() << Name << " (" << Data[Member++] << ")\n";
+          Elf_Word Ndx = Data[Member++];
+          const StringRef SecName = unwrapOrError(Obj->getSectionName(Sec));
+          auto It = SectionToGroup.insert({Ndx, {GroupName, SectionIndex}});
+          if (!It.second) {
+            StringRef GroupName = It.first->second.first;
+            uint32_t GroupIndex = It.first->second.second;
+            W.startLine() << "Error: " << SecName << " (" << Ndx
+                          << ") already in a group " + GroupName + " ("
+                          << GroupIndex << ")\n";
+            continue;
+          }
+          W.startLine() << SecName << " (" << Ndx << ")\n";
         }
       }
     }