[ELF] - Do not crash when object has multiple SHT_MIPS_OPTIONS

[grimar]

Summary

Issue was revealed by AFl and I was able to generate such object using yaml2obj,
it is reasonable to fix probably.

When object has more than one SHT_MIPS_OPTIONS, each except the last one is destroyed after
placing into Sections array.
Sections array contains dead pointers finally. LLD may crash then.

Do we want fixing it ?
If so I can prepare patch for fixing the same for SHT_MIPS_REGINFO and SHT_MIPS_ABIFLAGS.

[atanasyan]

LGTM

I think it is impossible to get multiple SHT_MIPS_OPTIONS sections in a real case. But as far as the fix so trivial let's do it.

[ruiu]

LGTM

ELF/InputFiles.cpp

328

Please include the filename. Error messages need to start with lowercase letters.

ELF/InputFiles.cpp

elf::ObjectFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
   case SHT_ARM_ATTRIBUTES:
     // FIXME: ARM meta-data section. At present attributes are ignored,
     // they can be used to reason about object compatibility.
     return &InputSection<ELFT>::Discarded;
   case SHT_MIPS_REGINFO:
     MipsReginfo.reset(new MipsReginfoInputSection<ELFT>(this, &Sec, Name));
     return MipsReginfo.get();
   case SHT_MIPS_OPTIONS:
+    if (MipsOptions)
+      fatal("Multiple SHT_MIPS_OPTIONS sections are not allowed");
     MipsOptions.reset(new MipsOptionsInputSection<ELFT>(this, &Sec, Name));
     return MipsOptions.get();
   case SHT_MIPS_ABIFLAGS:
     MipsAbiFlags.reset(new MipsAbiFlagsInputSection<ELFT>(this, &Sec, Name));
     return MipsAbiFlags.get();
   case SHT_RELA:
   case SHT_REL: {
     // This section contains relocation information.

test/ELF/invalid/mips-multiple-options.test

+# RUN: yaml2obj %s -o %t
+# RUN: not ld.lld %t -o %tout 2>&1 | FileCheck %s
+
+--- !ELF
+FileHeader:
+  Class:    ELFCLASS32
+  Data:     ELFDATA2LSB
+  Type:     ET_REL
+  Machine:  EM_MIPS
+  Flags:    [EF_MIPS_PIC, EF_MIPS_CPIC, EF_MIPS_ABI_O32, EF_MIPS_ARCH_32]
+
+Sections:
+  - Name:          .o1
+    Type:          SHT_MIPS_OPTIONS
+    Flags:         [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:  16
+    Content:       "010000000000000000000000"
+
+  - Name:          .o2
+    Type:          SHT_MIPS_OPTIONS
+    Flags:         [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:  16
+    Content:       "010000000000000000000000"
+
+# CHECK: Multiple SHT_MIPS_OPTIONS sections are not allowed