[llvm-readelf/obj] - Fix extended section symbol indices printed in warnings for MIPS GOT/PLT entries.

[grimar]

Summary

Recent refactoring introduced a symbol index argument for getFullSymbolName method,
which is only used for reporting error messages about invalid extended symbol indexes.

There are few issues in the implementation and we don't report correct symbol indices
when dumping MIPS GOT/PLT entries currently.

This patch adds test cases and fixes the issue.

[jhenderson]

Looks good, aside from one question.

llvm/tools/llvm-readobj/ELFDumper.cpp

6707–6708

I don't know MIPS at all. Is getGotDynSyms() equivalent to dynamic_symbols()?

[grimar]

llvm/tools/llvm-readobj/ELFDumper.cpp

6707–6708

No. getGotDynSyms was introduced by me in D87899 and it was a mistake. It returns GotDynSyms, which is:

GotDynSyms = DynSyms.drop_front(*DtGotSym);

where DynSyms == dynamic_symbols()

In this place we want to pass symbol index, so should really use dynamic_symbols()[0] instead of GotDynSyms[0].

This issue was catched by the test case.

llvm/test/tools/llvm-readobj/ELF/mips-got.test

 # SEC-SYMS-LLVM:          Section: .got (0x1)
 # SEC-SYMS-LLVM-NEXT:     Name: .got (0)
 # SEC-SYMS-LLVM-NEXT:   }
 # SEC-SYMS-LLVM-NEXT:   Entry {
 # SEC-SYMS-LLVM:          Section: Common (0xFFF2)
 # SEC-SYMS-LLVM-NEXT: warning: '[[FILE]]': unable to get section index for symbol with st_shndx = 0xfff2 (SHN_COMMON)
 # SEC-SYMS-LLVM-NEXT:     Name: <?> (0)
 # SEC-SYMS-LLVM-NEXT:   }
+# SEC-SYMS-LLVM-NEXT: Entry {
+# SEC-SYMS-LLVM:          Type: Section (0x3)
+# SEC-SYMS-LLVM-NEXT: warning: '[[FILE]]': extended symbol index (4) is past the end of the SHT_SYMTAB_SHNDX section of size 0
+# SEC-SYMS-LLVM-NEXT:     Section: Reserved (0xFFFF)
+# SEC-SYMS-LLVM-NEXT:     Name: <?> (0)
+# SEC-SYMS-LLVM-NEXT:   }
 # SEC-SYMS-LLVM-NEXT: ]
 
 # SEC-SYMS-GNU:      Global entries:
 # SEC-SYMS-GNU-NEXT:  {{.*}} Ndx Name
 # SEC-SYMS-GNU-NEXT: warning: '[[FILE]]': unable to get section index for symbol with st_shndx = 0xfff1 (SHN_ABS)
 # SEC-SYMS-GNU-NEXT:  {{.*}} ABS <?>
 # SEC-SYMS-GNU-NEXT:  {{.*}}   1 .got
 # SEC-SYMS-GNU-NEXT: warning: '[[FILE]]': unable to get section index for symbol with st_shndx = 0xfff2 (SHN_COMMON)
 # SEC-SYMS-GNU-NEXT:  {{.*}} COM <?>
+# SEC-SYMS-GNU-NEXT: warning: '[[FILE]]': extended symbol index (4) is past the end of the SHT_SYMTAB_SHNDX section of size 0
+# SEC-SYMS-GNU-NEXT:  {{.*}} RSV[0xffff] <?>
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS
 Sections:
Entries:
         Value: 0x1122
 DynamicSymbols:
   - Type:    STT_SECTION
     Index:   SHN_ABS
   - Type:    STT_SECTION
     Section: .got
   - Type:    STT_SECTION
     Index:   SHN_COMMON
+  - Type:    STT_SECTION
+    Index:   SHN_XINDEX

llvm/test/tools/llvm-readobj/ELF/mips-plt.test

 # SEC-SYMS-LLVM:            Section: .got.plt (0x2)
 # SEC-SYMS-LLVM-NEXT:       Name: .got.plt (0)
 # SEC-SYMS-LLVM-NEXT:     }
 # SEC-SYMS-LLVM-NEXT:     Entry {
 # SEC-SYMS-LLVM:            Section: Common (0xFFF2)
 # SEC-SYMS-LLVM-NEXT: warning: '[[FILE]]': unable to get section index for symbol with st_shndx = 0xfff2 (SHN_COMMON)
 # SEC-SYMS-LLVM-NEXT:       Name: <?> (0)
 # SEC-SYMS-LLVM-NEXT:     }
+# SEC-SYMS-LLVM-NEXT:     Entry {
+# SEC-SYMS-LLVM:            Type: Section (0x3)
+# SEC-SYMS-LLVM-NEXT: warning: '[[FILE]]': extended symbol index (4) is past the end of the SHT_SYMTAB_SHNDX section of size 0
+# SEC-SYMS-LLVM-NEXT:       Section: Reserved (0xFFFF)
+# SEC-SYMS-LLVM-NEXT:       Name: <?> (0)
+# SEC-SYMS-LLVM-NEXT:     }
 # SEC-SYMS-LLVM-NEXT:   ]
 # SEC-SYMS-LLVM-NEXT: }
 
 # SEC-SYMS-GNU:      PLT GOT:
 # SEC-SYMS-GNU:       Entries:
 # SEC-SYMS-GNU-NEXT:   Address          {{.*}} Ndx Name
 # SEC-SYMS-GNU-NEXT: warning: '[[FILE]]': unable to get section index for symbol with st_shndx = 0xfff1 (SHN_ABS)
 # SEC-SYMS-GNU-NEXT:   0000000000002010 {{.*}} ABS <?>
 # SEC-SYMS-GNU-NEXT:   0000000000002018 {{.*}}   2 .got.plt
 # SEC-SYMS-GNU-NEXT: warning: '[[FILE]]': unable to get section index for symbol with st_shndx = 0xfff2 (SHN_COMMON)
 # SEC-SYMS-GNU-NEXT:   0000000000002020 {{.*}} COM <?>
+# SEC-SYMS-GNU-NEXT: warning: '[[FILE]]': extended symbol index (4) is past the end of the SHT_SYMTAB_SHNDX section of size 0
+# SEC-SYMS-GNU-NEXT:   0000000000002028 {{.*}} RSV[0xffff] <?>
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_REL
   Machine: EM_MIPS
 Sections:
   - Name:    .rel.plt
     Type:    SHT_REL
     Flags:   [ SHF_ALLOC ]
     Address: 0x1000
     Link:    .dynsym
     Relocations:
       - Offset: 0x1
         Symbol: 1
         Type:   R_MIPS_JUMP_SLOT
       - Offset: 0x2
         Symbol: 2
         Type:   R_MIPS_JUMP_SLOT
       - Offset: 0x2
         Symbol: 3
         Type:   R_MIPS_JUMP_SLOT
+      - Offset: 0x3
+        Symbol: 4
+        Type:   R_MIPS_JUMP_SLOT
   - Name:    .got.plt
     Type:    SHT_PROGBITS
     Flags:   [ SHF_WRITE, SHF_ALLOC ]
     Address: 0x2000
-    Size:    40 ## (dynamic symbols number + 2) * 8
+    Size:    48 ## (dynamic symbols number + 2) * 8
   - Name: .dynamic
     Type: SHT_DYNAMIC
     Entries:
       - Tag:   DT_JMPREL
         Value: 0x1000
       - Tag:   DT_MIPS_PLTGOT
         Value: 0x2000
 DynamicSymbols:
   - Type:    STT_SECTION
     Index:   SHN_ABS
   - Type:    STT_SECTION
     Section: .got.plt
   - Type:    STT_SECTION
     Index:   SHN_COMMON
+  - Type:    STT_SECTION
+    Index:   SHN_XINDEX

llvm/tools/llvm-readobj/ELFDumper.cpp

public:
   Entries getLocalEntries() const;
   Entries getGlobalEntries() const;
   Entries getOtherEntries() const;
   Entries getPltEntries() const;
 
   uint64_t getGotAddress(const Entry * E) const;
   int64_t getGotOffset(const Entry * E) const;
   const Elf_Sym *getGotSym(const Entry *E) const;
-  Elf_Sym_Range getGotDynSyms() const { return GotDynSyms; }
 
   uint64_t getPltAddress(const Entry * E) const;
   const Elf_Sym *getPltSym(const Entry *E) const;
 
   StringRef getPltStrTable() const { return PltStrTable; }
   const Elf_Shdr *getPltSymTable() const { return PltSymTable; }
 
 private:
if (ELFT::Is64Bits)
       OS << "           Address     Access          Initial         Sym.Val."
          << " Type    Ndx Name\n";
     else
       OS << "   Address     Access  Initial Sym.Val. Type    Ndx Name\n";
     for (auto &E : Parser.getGlobalEntries()) {
       const Elf_Sym &Sym = *Parser.getGotSym(&E);
       const Elf_Sym &FirstSym = this->dumper().dynamic_symbols()[0];
       std::string SymName = this->dumper().getFullSymbolName(
-          Sym, &FirstSym - &Sym, this->dumper().getDynamicStringTable(), false);
+          Sym, &Sym - &FirstSym, this->dumper().getDynamicStringTable(), false);
 
       OS.PadToColumn(2);
       OS << to_string(format_hex_no_prefix(Parser.getGotAddress(&E), 8 + Bias));
       OS.PadToColumn(11 + Bias);
       OS << to_string(format_decimal(Parser.getGotOffset(&E), 6)) + "(gp)";
       OS.PadToColumn(22 + Bias);
       OS << to_string(format_hex_no_prefix(E, 8 + Bias));
       OS.PadToColumn(31 + 2 * Bias);
if (!Parser.getPltEntries().empty()) {
     OS << " Entries:\n";
     OS << "   Address  Initial Sym.Val. Type    Ndx Name\n";
     for (auto &E : Parser.getPltEntries()) {
       const Elf_Sym &Sym = *Parser.getPltSym(&E);
       const Elf_Sym &FirstSym =
           *cantFail(this->Obj.template getEntry<const Elf_Sym>(
               *Parser.getPltSymTable(), 0));
       std::string SymName = this->dumper().getFullSymbolName(
-          Sym, &FirstSym - &Sym, this->dumper().getDynamicStringTable(), false);
+          Sym, &Sym - &FirstSym, this->dumper().getDynamicStringTable(), false);
 
       OS.PadToColumn(2);
       OS << to_string(format_hex_no_prefix(Parser.getPltAddress(&E), 8 + Bias));
       OS.PadToColumn(11 + Bias);
       OS << to_string(format_hex_no_prefix(E, 8 + Bias));
       OS.PadToColumn(20 + 2 * Bias);
       OS << to_string(format_hex_no_prefix(Sym.st_value, 8 + Bias));
       OS.PadToColumn(29 + 3 * Bias);
if (Parser.IsStatic)
     return;
 
   {
     ListScope GS(W, "Global entries");
     for (auto &E : Parser.getGlobalEntries()) {
       DictScope D(W, "Entry");
 
       PrintEntry(&E);
 
       const Elf_Sym &Sym = *Parser.getGotSym(&E);
       W.printHex("Value", Sym.st_value);
       W.printEnum("Type", Sym.getType(), makeArrayRef(ElfSymbolTypes));
-      printSymbolSection(Sym, &Sym - this->dumper().dynamic_symbols().begin());
+
+      const unsigned SymIndex = &Sym - this->dumper().dynamic_symbols().begin();
+      printSymbolSection(Sym, SymIndex);
 
       std::string SymName = this->dumper().getFullSymbolName(
-          Sym, &Sym - &Parser.getGotDynSyms()[0],
-          this->dumper().getDynamicStringTable(), true);
+          Sym, SymIndex, this->dumper().getDynamicStringTable(), true);
       W.printNumber("Name", SymName, Sym.st_name);
     }
   }
 
   W.printNumber("Number of TLS and multi-GOT entries",
                 uint64_t(Parser.getOtherEntries().size()));
 }