[ELF] - Improve diagnostics on duplicate STT_SECTION symbol.

[grimar]

Summary

Global symbols of type STT_SECTION has section field null when reference
relocation sections, for which we do not create input sections:

• Type: STT_SECTION Section: .rela.text

In case of duplicate symbol lld crashed trying to access nullptr.

[ruiu]

This is not an obvious patch to handle corrupted input, so I'm honestly not in favor of it.

[grimar]

Rebased after latest changes, it is much simpler now.

[grimar]

In D25513#569710, @ruiu wrote:

This is not an obvious patch to handle corrupted input, so I'm honestly not in favor of it.

Latest changes in LLD allowed to simplify this. Is it ok now ?

[ruiu]

test/ELF/invalid/report-duplicates.test

3

This error message doesn't make sense.

[davide]

test/ELF/invalid/report-duplicates.test

3

ehm, a symbol with an empty name reported as duplicated to the use is not really helpful (if not misleading).

[• rafael]

How were we crashing?

The empty name I assume is orthogonal, no? Both symbols could be named foo for example.

[grimar]

Given that no well behaved producer creates a global STT_SECTION and
this was no longer crashing, abandoning it.

ELF/SymbolTable.cpp

 }
 
 static void reportDuplicate(SymbolBody *Existing, InputFile *NewFile) {
   print("duplicate symbol " + conflictMsg(Existing, NewFile));
 }
 
 template <class ELFT>
 static void reportDuplicate(SymbolBody *Existing,
-                            InputSectionBase<ELFT> *ErrSec,
+                            InputSectionBase<ELFT> *ErrSec, InputFile *File,
                             typename ELFT::uint ErrOffset) {
   DefinedRegular<ELFT> *D = dyn_cast<DefinedRegular<ELFT>>(Existing);
   if (!D || !D->Section || !ErrSec) {
-    reportDuplicate(Existing, ErrSec ? ErrSec->getFile() : nullptr);
+    reportDuplicate(Existing, File);
     return;
   }
 
   std::string OldLoc = getLocation(*D->Section, D->Value);
   std::string NewLoc = getLocation(*ErrSec, ErrOffset);
 
   print(NewLoc + ": duplicate symbol '" + maybeDemangle(Existing->getName()) +
         "'");
Symbol *SymbolTable<ELFT>::addRegular(StringRef Name, uint8_t StOther,
   bool WasInserted;
   std::tie(S, WasInserted) = insert(Name, Type, StOther & 3,
                                     /*CanOmitFromDynSym*/ false, File);
   int Cmp = compareDefinedNonCommon(S, WasInserted, Binding);
   if (Cmp > 0)
     replaceBody<DefinedRegular<ELFT>>(S, Name, StOther, Type, Value, Size,
                                       Section, File);
   else if (Cmp == 0)
-    reportDuplicate(S->body(), Section, Value);
+    reportDuplicate(S->body(), Section, File, Value);
   return S;
 }
 
 template <typename ELFT>
 Symbol *SymbolTable<ELFT>::addSynthetic(StringRef N, OutputSectionBase *Section,
                                         uintX_t Value, uint8_t StOther) {
   Symbol *S;
   bool WasInserted;

test/ELF/invalid/report-duplicates.test

+# RUN: yaml2obj %s -o %t.o
+# RUN: not ld.lld %t.o -o %tout 2>&1 | FileCheck %s
+# CHECK: duplicate symbol '' in {{.*}}.o and {{.*}}.o
+
+--- !ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000010
+    Content:         "00000000"
+  - Name:            .rela.text
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    Info:            .text
+    Relocations:
+Symbols:
+  Global:
+    - Type:            STT_SECTION
+      Section:         .rela.text
+    - Type:            STT_SECTION
+      Section:         .rela.text