[llvm-readobj] - Refactor the MipsGOTParser<ELFT> to stop using report_fatal_error().

[grimar]

Summary

MipsGOTParser is a helper class that is used to dump MIPS GOT and PLT.
There is a problem with it: it might call report_fatal_error() on invalid input.
When this happens, the tool reports a crash:

# command stderr:
LLVM ERROR: Cannot find PLTGOT dynamic table tag.
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backt
race.
Stack dump:
...

Such error were not tested. In this patch I've refactored MipsGOTParser:

I've splitted handling of GOT and PLT to separate methods. This allows to propagate
any possible errors to caller and should allow to dump the PLT when something is wrong
with the GOT and vise versa in the future.

I've added tests for each report_fatal_error()
and now calling the reportError instead. In the future we might want to switch to
reporting warnings, but it requres the additional testing and should
be performed independently.

I've kept unwrapOrError calls untouched for now as I'd like to focus on eliminating
report_fatal_error calls in this patch only (to stop crashing on invalid inputs
when doing inputs fuzzing).

[grimar]

• Remove unused YAML line.

[atanasyan]

LGTM. Thanks

[MaskRay]

Some nits.

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

7

# prepending can be committed separately.

llvm/tools/llvm-readobj/ELFDumper.cpp

3034

The canonical term is dynamic tag, not dynamic table tag.

[jhenderson]

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

7

+1 to this (in both tests)

llvm/tools/llvm-readobj/ELFDumper.cpp

3087–3094

These two cases don't appear to have tests?

Also, the errors should be "not empty" -> "non-empty" and have lower-case first letters.

[grimar]

• Addressed review comments.

llvm/tools/llvm-readobj/ELFDumper.cpp

3034

Fixed.

3087–3094

Oh, right. I've missed them for unknown reason. I've added tests for these 2.

[jhenderson]

LGTM, with message fix.

llvm/tools/llvm-readobj/ELFDumper.cpp

3087–3094

not empty -> non-empty

(in both errors still)

[grimar]

llvm/tools/llvm-readobj/ELFDumper.cpp

3087–3094

(in both errors still)

Sorry!

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

 # GNU-GOT-STATIC-NEXT:   00410110 -32752(gp) 00000000 Lazy resolver
 # GNU-GOT-STATIC-NEXT:   00410114 -32748(gp) 80000000 Module pointer (GNU extension)
 
 # GNU-GOT-STATIC:       Local entries:
 # GNU-GOT-STATIC-NEXT:    Address     Access  Initial
 # GNU-GOT-STATIC-NEXT:   00410118 -32744(gp) 00400000
 # GNU-GOT-STATIC-NEXT:   0041011c -32740(gp) 00400100
 # GNU-GOT-STATIC-NEXT:   00410120 -32736(gp) 00400104
+
+## Check we report errors when dynamic tags, needed for dumping GOT, are missing.
+
+# RUN: yaml2obj --docnum=1 -DTAG1=DT_MIPS_LOCAL_GOTNO -DTAG2=DT_MIPS_GOTSYM %s -o %t.err1.o
+# RUN: not llvm-readobj -A %t.err1.o 2>&1 | FileCheck %s -DFILE=%t.err1.o -check-prefix ERR1
+
+# ERR1: error: '[[FILE]]': cannot find PLTGOT dynamic tag
+
+# RUN: yaml2obj --docnum=1 -DTAG1=DT_PLTGOT -DTAG2=DT_MIPS_GOTSYM %s -o %t.err2.o
+# RUN: not llvm-readobj -A %t.err2.o 2>&1 | FileCheck %s -DFILE=%t.err2.o -check-prefix ERR2
+
+# ERR2: error: '[[FILE]]': cannot find MIPS_LOCAL_GOTNO dynamic tag
+
+# RUN: yaml2obj --docnum=1 -DTAG1=DT_PLTGOT -DTAG2=DT_MIPS_LOCAL_GOTNO %s -o %t.err3.o
+# RUN: not llvm-readobj -A %t.err3.o 2>&1 | FileCheck %s -DFILE=%t.err3.o -check-prefix ERR3
+
+# ERR3: error: '[[FILE]]': cannot find MIPS_GOTSYM dynamic tag
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_MIPS
+Sections:
+  - Name: .dynamic
+    Type: SHT_DYNAMIC
+    Entries:
+      - Tag:   [[TAG1]]
+        Value: 0
+      - Tag:   [[TAG2]]
+        Value: 0
+      - Tag:   DT_NULL
+        Value: 0
+DynamicSymbols: []

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

 # RUN: llvm-readobj -A %p/Inputs/got-plt.exe.elf-mipsel | FileCheck %s
 # RUN: llvm-readelf -A %p/Inputs/got-plt.exe.elf-mipsel | FileCheck --check-prefix=GNU %s
 
 # CHECK:      PLT GOT {
 # CHECK-NEXT:   Reserved entries [
 # CHECK-NEXT:     Entry {
 # CHECK-NEXT:       Address: 0x410814
 # CHECK-NEXT:       Initial: 0x0
 # CHECK-NEXT:       Purpose: PLT lazy resolver
 # CHECK-NEXT:     }
 # CHECK-NEXT:     Entry {
 # CHECK-NEXT:       Address: 0x410818
 # CHECK-NEXT:       Initial: 0x0
 # CHECK-NEXT:       Purpose: Module pointer
 # CHECK-NEXT:     }

 # GNU-NEXT:    Address  Initial Purpose
 # GNU-NEXT:   00410814 00000000 PLT lazy resolver
 # GNU-NEXT:   00410818 00000000 Module pointer
 
 # GNU:       Entries:
 # GNU-NEXT:    Address  Initial Sym.Val. Type    Ndx Name
 # GNU-NEXT:   0041081c 004007c0 00000000 FUNC    UND puts
 # GNU-NEXT:   00410820 004007c0 00000000 FUNC    UND __libc_start_main
+
+## Check we report errors when dynamic tags, needed for dumping PLT, are missing.
+
+# RUN: yaml2obj --docnum=1 -DTAG=DT_MIPS_PLTGOT %s -o %t.err1.o
+# RUN: not llvm-readobj -A %t.err1.o 2>&1 | FileCheck %s -DFILE=%t.err1.o --check-prefix=ERR1
+
+# ERR1: error: '[[FILE]]': cannot find JMPREL dynamic tag
+
+# RUN: yaml2obj --docnum=1 -DTAG=DT_JMPREL %s -o %t.err2.o
+# RUN: not llvm-readobj -A %t.err2.o 2>&1 | FileCheck %s -DFILE=%t.err2.o --check-prefix=ERR2
+
+# ERR2: error: '[[FILE]]': cannot find MIPS_PLTGOT dynamic tag
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_MIPS
+Sections:
+  - Name: .dynamic
+    Type: SHT_DYNAMIC
+    Entries:
+      - Tag:   [[TAG]]
+        Value: 0
+      - Tag:   DT_NULL
+        Value: 0
+
+## Check we report errors when we are unable to find PLTGOT/JMPREL sections.
+# RUN: yaml2obj --docnum=2 %s -DVAL1=0xffff -o %t.err3.o
+# RUN: not llvm-readobj -A %t.err3.o 2>&1 | FileCheck %s -DFILE=%t.err3.o -check-prefix ERR3
+
+# ERR3: error: '[[FILE]]': there is no non-empty PLTGOT section at 0xffff
+
+# RUN: yaml2obj --docnum=2 %s -DVAL2=0xffff -o %t.err4.o
+# RUN: not llvm-readobj -A %t.err4.o 2>&1 | FileCheck %s -DFILE=%t.err4.o -check-prefix ERR4
+
+# ERR4: error: '[[FILE]]': there is no non-empty RELPLT section at 0xffff
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_MIPS
+Sections:
+  - Name: .dynamic
+    Type: SHT_DYNAMIC
+    Entries:
+      - Tag:   DT_MIPS_PLTGOT
+        Value: [[VAL1=0]]
+      - Tag:   DT_JMPREL
+        Value: [[VAL2=0]]
+      - Tag:   DT_NULL
+        Value: 0
+DynamicSymbols: []

llvm/tools/llvm-readobj/ELFDumper.cpp

case EM_RISCV:
     break;
   case EM_MIPS: {
     ELFDumperStyle->printMipsABIFlags(ObjF);
     printMipsOptions();
     printMipsReginfo();
 
     MipsGOTParser<ELFT> Parser(Obj, ObjF->getFileName(), dynamic_table(),
                                dynamic_symbols());
-    if (Parser.hasGot())
+    if (Error E = Parser.findGOT(dynamic_table(), dynamic_symbols()))
+      reportError(std::move(E), ObjF->getFileName());
+    else if (!Parser.isGotEmpty())
       ELFDumperStyle->printMipsGOT(Parser);
-    if (Parser.hasPlt())
+
+    if (Error E = Parser.findPLT(dynamic_table()))
+      reportError(std::move(E), ObjF->getFileName());
+    else if (!Parser.isPltEmpty())
       ELFDumperStyle->printMipsPLT(Parser);
     break;
   }
   default:
     break;
   }
 }
 
public:
   using Entry = typename ELFO::Elf_Addr;
   using Entries = ArrayRef<Entry>;
 
   const bool IsStatic;
   const ELFO * const Obj;
 
   MipsGOTParser(const ELFO *Obj, StringRef FileName, Elf_Dyn_Range DynTable,
                 Elf_Sym_Range DynSyms);
+  Error findGOT(Elf_Dyn_Range DynTable, Elf_Sym_Range DynSyms);
+  Error findPLT(Elf_Dyn_Range DynTable);
 
-  bool hasGot() const { return !GotEntries.empty(); }
-  bool hasPlt() const { return !PltEntries.empty(); }
+  bool isGotEmpty() const { return GotEntries.empty(); }
+  bool isPltEmpty() const { return PltEntries.empty(); }
 
   uint64_t getGp() const;
 
   const Entry *getGotLazyResolver() const;
   const Entry *getGotModulePointer() const;
   const Entry *getPltLazyResolver() const;
   const Entry *getPltModulePointer() const;
 

 } // end anonymous namespace
 
 template <class ELFT>
 MipsGOTParser<ELFT>::MipsGOTParser(const ELFO *Obj, StringRef FileName,
                                    Elf_Dyn_Range DynTable,
                                    Elf_Sym_Range DynSyms)
     : IsStatic(DynTable.empty()), Obj(Obj), GotSec(nullptr), LocalNum(0),
       GlobalNum(0), PltSec(nullptr), PltRelSec(nullptr), PltSymTable(nullptr),
-      FileName(FileName) {
+      FileName(FileName) {}
+
+template <class ELFT>
+Error MipsGOTParser<ELFT>::findGOT(Elf_Dyn_Range DynTable,
+                                   Elf_Sym_Range DynSyms) {
   // See "Global Offset Table" in Chapter 5 in the following document
   // for detailed GOT description.
   // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
 
   // Find static GOT secton.
   if (IsStatic) {
     GotSec = findSectionByName(*Obj, FileName, ".got");
     if (!GotSec)
-      return;
+      return Error::success();
 
     ArrayRef<uint8_t> Content =
         unwrapOrError(FileName, Obj->getSectionContents(GotSec));
     GotEntries = Entries(reinterpret_cast<const Entry *>(Content.data()),
                          Content.size() / sizeof(Entry));
     LocalNum = GotEntries.size();
-    return;
+    return Error::success();
   }
 
-  // Lookup dynamic table tags which define GOT/PLT layouts.
+  // Lookup dynamic table tags which define the GOT layout.
   Optional<uint64_t> DtPltGot;
   Optional<uint64_t> DtLocalGotNum;
   Optional<uint64_t> DtGotSym;
-  Optional<uint64_t> DtMipsPltGot;
-  Optional<uint64_t> DtJmpRel;
   for (const auto &Entry : DynTable) {
     switch (Entry.getTag()) {
     case ELF::DT_PLTGOT:
       DtPltGot = Entry.getVal();
       break;
     case ELF::DT_MIPS_LOCAL_GOTNO:
       DtLocalGotNum = Entry.getVal();
       break;
     case ELF::DT_MIPS_GOTSYM:
       DtGotSym = Entry.getVal();
       break;
-    case ELF::DT_MIPS_PLTGOT:
-      DtMipsPltGot = Entry.getVal();
-      break;
-    case ELF::DT_JMPREL:
-      DtJmpRel = Entry.getVal();
-      break;
     }
   }
 
-  // Find dynamic GOT section.
-  if (DtPltGot || DtLocalGotNum || DtGotSym) {
-    if (!DtPltGot)
-      report_fatal_error("Cannot find PLTGOT dynamic table tag.");
-    if (!DtLocalGotNum)
-      report_fatal_error("Cannot find MIPS_LOCAL_GOTNO dynamic table tag.");
-    if (!DtGotSym)
-      report_fatal_error("Cannot find MIPS_GOTSYM dynamic table tag.");
+  if (!DtPltGot && !DtLocalGotNum && !DtGotSym)
+    return Error::success();
+
+    return createError("cannot find PLTGOT dynamic tag");
+    return createError("cannot find MIPS_LOCAL_GOTNO dynamic tag");
+    return createError("cannot find MIPS_GOTSYM dynamic tag");
 
-    size_t DynSymTotal = DynSyms.size();
-    if (*DtGotSym > DynSymTotal)
-      reportError(
-          createError("MIPS_GOTSYM exceeds a number of dynamic symbols"),
-          FileName);
+    return createError("MIPS_GOTSYM exceeds a number of dynamic symbols");
 
-    GotSec = findNotEmptySectionByAddress(Obj, FileName, *DtPltGot);
-    if (!GotSec)
-      reportError(createError("There is no not empty GOT section at 0x" +
-                              Twine::utohexstr(*DtPltGot)),
-                  FileName);
+    return createError("there is no non-empty GOT section at 0x" +
+                       Twine::utohexstr(*DtPltGot));
 
-    LocalNum = *DtLocalGotNum;
-    GlobalNum = DynSymTotal - *DtGotSym;
 
-    ArrayRef<uint8_t> Content =
-        unwrapOrError(FileName, Obj->getSectionContents(GotSec));
-    GotEntries = Entries(reinterpret_cast<const Entry *>(Content.data()),
-                         Content.size() / sizeof(Entry));
-    GotDynSyms = DynSyms.drop_front(*DtGotSym);
+
+  return Error::success();
+}
+
+template <class ELFT>
+Error MipsGOTParser<ELFT>::findPLT(Elf_Dyn_Range DynTable) {
+  // Lookup dynamic table tags which define the PLT layout.
+  Optional<uint64_t> DtMipsPltGot;
+  Optional<uint64_t> DtJmpRel;
+  for (const auto &Entry : DynTable) {
+    switch (Entry.getTag()) {
+    case ELF::DT_MIPS_PLTGOT:
+      DtMipsPltGot = Entry.getVal();
+      break;
+    case ELF::DT_JMPREL:
+      DtJmpRel = Entry.getVal();
+      break;
+    }
   }
 
+  if (!DtMipsPltGot && !DtJmpRel)
+    return Error::success();
+
   // Find PLT section.
-  if (DtMipsPltGot || DtJmpRel) {
-    if (!DtMipsPltGot)
-      report_fatal_error("Cannot find MIPS_PLTGOT dynamic table tag.");
-    if (!DtJmpRel)
-      report_fatal_error("Cannot find JMPREL dynamic table tag.");
+    return createError("cannot find MIPS_PLTGOT dynamic tag");
+    return createError("cannot find JMPREL dynamic tag");
 
-    PltSec = findNotEmptySectionByAddress(Obj, FileName, * DtMipsPltGot);
-    if (!PltSec)
-      report_fatal_error("There is no not empty PLTGOT section at 0x " +
-                         Twine::utohexstr(*DtMipsPltGot));
+  PltSec = findNotEmptySectionByAddress(Obj, FileName, *DtMipsPltGot);
+    return createError("there is no non-empty PLTGOT section at 0x" +
 
-    PltRelSec = findNotEmptySectionByAddress(Obj, FileName, * DtJmpRel);
-    if (!PltRelSec)
-      report_fatal_error("There is no not empty RELPLT section at 0x" +
-                         Twine::utohexstr(*DtJmpRel));
+  PltRelSec = findNotEmptySectionByAddress(Obj, FileName, *DtJmpRel);
+    return createError("there is no non-empty RELPLT section at 0x" +
 
-    ArrayRef<uint8_t> PltContent =
-        unwrapOrError(FileName, Obj->getSectionContents(PltSec));
-    PltEntries = Entries(reinterpret_cast<const Entry *>(PltContent.data()),
-                         PltContent.size() / sizeof(Entry));
 
-    PltSymTable = unwrapOrError(FileName, Obj->getSection(PltRelSec->sh_link));
-    PltStrTable =
-        unwrapOrError(FileName, Obj->getStringTableForSymtab(*PltSymTable));
-  }
+
+  return Error::success();
 }
 
 template <class ELFT> uint64_t MipsGOTParser<ELFT>::getGp() const {
   return GotSec->sh_addr + 0x7ff0;
 }
 
 template <class ELFT>
 const typename MipsGOTParser<ELFT>::Entry *