[ELF] - Don't crash on multiple SHT_MIPS_REGINFO/SHT_MIPS_ABIFLAGS sections.

[grimar]

Summary

In continue of D25555, this patch fixes possible crash when
we have multiple SHT_MIPS_REGINFO or SHT_MIPS_ABIFLAGS sections.
yaml2obj was used to produce such objects.

[atanasyan]

LGTM
Thanks

ELF/InputFiles.cpp

elf::ObjectFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
   StringRef Name = check(this->ELFObj.getSectionName(&Sec));
 
   switch (Sec.sh_type) {
   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:
+    if (MipsReginfo)
+      fatal(getFilename(this) +
+            ": multiple SHT_MIPS_REGINFO sections are not allowed");
     MipsReginfo.reset(new MipsReginfoInputSection<ELFT>(this, &Sec, Name));
     return MipsReginfo.get();
   case SHT_MIPS_OPTIONS:
     if (MipsOptions)
       fatal(getFilename(this) +
             ": multiple SHT_MIPS_OPTIONS sections are not allowed");
     MipsOptions.reset(new MipsOptionsInputSection<ELFT>(this, &Sec, Name));
     return MipsOptions.get();
   case SHT_MIPS_ABIFLAGS:
+    if (MipsAbiFlags)
+      fatal(getFilename(this) +
+            ": multiple SHT_MIPS_ABIFLAGS sections are not allowed");
     MipsAbiFlags.reset(new MipsAbiFlagsInputSection<ELFT>(this, &Sec, Name));
     return MipsAbiFlags.get();
   case SHT_RELA:
   case SHT_REL: {
     // This section contains relocation information.
     // If -r is given, we do not interpret or apply relocation
     // but just copy relocation sections to output.
     if (Config->Relocatable)

test/ELF/invalid/mips-multiple-abiflags.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:          .foo1
+    Type:          SHT_MIPS_ABIFLAGS
+    ISA:           MIPS64
+
+  - Name:          .foo2
+    Type:          SHT_MIPS_ABIFLAGS
+    ISA:           MIPS64
+
+# CHECK: multiple SHT_MIPS_ABIFLAGS sections are not allowed

test/ELF/invalid/mips-multiple-reginfo.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:          .foo1
+    Type:          SHT_MIPS_REGINFO
+    Flags:         [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:  16
+    Content:       "000000000000000000000000000000000000000000000000"
+
+  - Name:          .foo2
+    Type:          SHT_MIPS_REGINFO
+    Flags:         [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:  16
+    Content:       "000000000000000000000000000000000000000000000000"
+
+# CHECK: multiple SHT_MIPS_REGINFO sections are not allowed