[ELF] - Check that .dynsym is present in DSO if SHT_GNU_versym section is.

[grimar]

Summary

When we have SHT_GNU_versym section, it is should be associated with symbol table
section. Usually (and in out implementation) it is .dynsym.
In case when .dynsym is absent (due to broken object for example),
lld crashes in parseVerdefs() when accesses null pointer:

Versym = reinterpret_cast<const Elf_Versym *>(this->ELFObj.base() +
                                              VersymSec->sh_offset) +
         this->Symtab->sh_info;

[ruiu]

ELF/InputFiles.cpp

5

Can this actually happen?

[grimar]

• Changed testcase to use yaml2obj.
• Restored check removed by mistake.

[grimar]

ELF/InputFiles.cpp

5

I was able to get it using yaml2obj. That is the only produccer I know, but that seems enough to fix ?
Updated testcase.

ELF/SymbolTable.cpp

79

I used this check so we able to error() instead of fatal().
fatal() is more consistent for broken inputs, but I think error() is still more preferable sometimes (at least it is better for case when lld used as a lib) ?

[• rafael]

LGTM

ELF/InputFiles.cpp

 //===- InputFiles.cpp -----------------------------------------------------===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "InputFiles.h"
 #include "Driver.h"
 #include "ELFCreator.h"
 #include "Error.h"
case SHT_GNU_versym:
       this->VersymSec = &Sec;
       break;
     case SHT_GNU_verdef:
       this->VerdefSec = &Sec;
       break;
     }
   }
 
+  if (this->VersymSec && !this->Symtab)
+    error("SHT_GNU_versym should be associated with symbol table");
+
   this->initStringTable();
 
   // DSOs are identified by soname, and they usually contain
   // DT_SONAME tag in their header. But if they are missing,
   // filenames are used as default sonames.
   SoName = sys::path::filename(this->getName());
 
   if (!DynamicSec)

ELF/SymbolTable.cpp

template <class ELFT> void SymbolTable<ELFT>::addFile(InputFile *File) {
 
   if (Config->Trace)
     outs() << getFilename(File) << "\n";
 
   // .so file
   if (auto *F = dyn_cast<SharedFile<ELFT>>(File)) {
     // DSOs are uniquified not by filename but by soname.
     F->parseSoName();
-    if (!SoNames.insert(F->getSoName()).second)
+    if (HasError || !SoNames.insert(F->getSoName()).second)
       return;
     SharedFiles.push_back(F);
     F->parseRest();
     return;
   }
 
   // LLVM bitcode file
   if (auto *F = dyn_cast<BitcodeFile>(File)) {

test/ELF/invalid/verdef-no-symtab.test

+# RUN: yaml2obj %s -o %t
+# RUN: not ld.lld %t -o %tout 2>&1 | FileCheck %s
+
+## When we have SHT_GNU_versym section, it is should be associated
+## with symbol table section.
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_DYN
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .versym
+    Type:            SHT_GNU_versym
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x1
+    Content:         "00000000"
+
+  - Name:            .verdef
+    Type:            SHT_GNU_verdef
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x1
+    Content:         "00000000"
+
+
+# CHECK: SHT_GNU_versym should be associated with symbol table