[llvm-readobj] - Refine error reporting in MipsGOTParser<ELFT> helper.

[grimar]

Summary

This is a follow-up for D83225. This does the following:

1. Adds missing tests for existent errors.
2. Stops using unwrapOrError to propagate errors to caller. (I am trying to get rid of all unwrapOrErr calls in the llvm-readelf code).
3. Improves error messages reported slightly.

[jhenderson]

LGTM, with one nit.

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

127

"to dump the PLTGOT properly"

(GOT stands for Global Offset Table, so no need to say "table" again).

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

- Name: .dynamic
     Entries:
       - Tag:   [[TAG1]]
         Value: 0
       - Tag:   [[TAG2]]
         Value: 0
       - Tag:   DT_NULL
         Value: 0
 DynamicSymbols: []
+
+# RUN: yaml2obj --docnum=2 -DVAL1=0xffff %s -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]]': DT_MIPS_GOTSYM value (65535) exceeds the number of dynamic symbols (1)
+
+# RUN: yaml2obj --docnum=2 -DVAL2=0xffff %s -o %t.err5.o
+# RUN: not llvm-readobj -A %t.err5.o 2>&1 | FileCheck %s -DFILE=%t.err5.o -check-prefix=ERR5
+
+# ERR5: error: '[[FILE]]': there is no non-empty GOT 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_LOCAL_GOTNO
+        Value: 0
+      - Tag:   DT_MIPS_GOTSYM
+        Value: [[VAL1=0]]
+      - Tag:   DT_PLTGOT
+        Value: [[VAL2=0]]
+DynamicSymbols: []

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

- Name: .dynamic
     Type: SHT_DYNAMIC
     Entries:
       - Tag:   DT_MIPS_PLTGOT
         Value: [[VAL1=0]]
       - Tag:   DT_JMPREL
         Value: [[VAL2=0]]
       - Tag:   DT_NULL
         Value: 0
+  - Name:    .foo
+    Type:    SHT_PROGBITS
+    Address: 0x100
+    ShSize:  0xffffffff
+    Link:    [[LINK=0x1]]
 DynamicSymbols: []
+
+## Check we report errors when we are unable to dump PLTGOT table properly.
+
+# RUN: yaml2obj --docnum=2 -DVAL1=0x100 %s -o %t.err5.o
+# RUN: not llvm-readobj -A %t.err5.o 2>&1 | FileCheck %s -DFILE=%t.err5.o -check-prefix ERR5
+
+# ERR5: error: '[[FILE]]': unable to read PLTGOT section content: section [index 2] has a sh_offset (0x70) + sh_size (0xffffffff) that is greater than the file size (0x280)
+
+# RUN: yaml2obj --docnum=2 -DVAL2=0x100 -DLINK=0xaaaaaaaa %s -o %t.err6.o
+# RUN: not llvm-readobj -A %t.err6.o 2>&1 | FileCheck %s -DFILE=%t.err6.o -check-prefix ERR6
+
+# ERR6: error: '[[FILE]]': unable to get a symbol table linked to the RELPLT section with index 2: invalid section index: 2863311530
+
+# RUN: yaml2obj --docnum=2 -DVAL2=0x100 %s -o %t.err7.o
+# RUN: not llvm-readobj -A %t.err7.o 2>&1 | FileCheck %s -DFILE=%t.err7.o -check-prefix ERR7
+
+# ERR7: error: '[[FILE]]': unable to get a string table for the symbol table with index 1: invalid sh_type for symbol table, expected SHT_SYMTAB or SHT_DYNSYM

llvm/tools/llvm-readobj/ELFDumper.cpp

if (!DtPltGot)
     return createError("cannot find PLTGOT dynamic tag");
   if (!DtLocalGotNum)
     return createError("cannot find MIPS_LOCAL_GOTNO dynamic tag");
   if (!DtGotSym)
     return createError("cannot find MIPS_GOTSYM dynamic tag");
 
   size_t DynSymTotal = DynSyms.size();
   if (*DtGotSym > DynSymTotal)
-    return createError("MIPS_GOTSYM exceeds a number of dynamic symbols");
+    return createError("DT_MIPS_GOTSYM value (" + Twine(*DtGotSym) +
+                       ") exceeds the number of dynamic symbols (" +
+                       Twine(DynSymTotal) + ")");
 
   GotSec = findNotEmptySectionByAddress(Obj, FileName, *DtPltGot);
   if (!GotSec)
     return createError("there is no non-empty GOT section at 0x" +
                        Twine::utohexstr(*DtPltGot));
 
   LocalNum = *DtLocalGotNum;
   GlobalNum = DynSymTotal - *DtGotSym;
if (!PltSec)
     return createError("there is no non-empty PLTGOT section at 0x" +
                        Twine::utohexstr(*DtMipsPltGot));
 
   PltRelSec = findNotEmptySectionByAddress(Obj, FileName, *DtJmpRel);
   if (!PltRelSec)
     return createError("there is no non-empty RELPLT section at 0x" +
                        Twine::utohexstr(*DtJmpRel));
 
-  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));
+  if (Expected<ArrayRef<uint8_t>> PltContentOrErr =
+          Obj->getSectionContents(PltSec))
+    PltEntries =
+        Entries(reinterpret_cast<const Entry *>(PltContentOrErr->data()),
+                PltContentOrErr->size() / sizeof(Entry));
+  else
+    return createError("unable to read PLTGOT section content: " +
+                       toString(PltContentOrErr.takeError()));
+
+  if (Expected<const Elf_Shdr *> PltSymTableOrErr =
+          Obj->getSection(PltRelSec->sh_link)) {
+    PltSymTable = *PltSymTableOrErr;
+  } else {
+    unsigned SecNdx = PltRelSec - &cantFail(Obj->sections()).front();
+    return createError("unable to get a symbol table linked to the RELPLT "
+                       "section with index " +
+                       Twine(SecNdx) + ": " +
+                       toString(PltSymTableOrErr.takeError()));
+  }
+
+  if (Expected<StringRef> StrTabOrErr =
+          Obj->getStringTableForSymtab(*PltSymTable)) {
+    PltStrTable = *StrTabOrErr;
+  } else {
+    unsigned SecNdx = PltSymTable - &cantFail(Obj->sections()).front();
+    return createError(
+        "unable to get a string table for the symbol table with index " +
+        Twine(SecNdx) + ": " + toString(StrTabOrErr.takeError()));
+  }
 
   return Error::success();
 }
 
 template <class ELFT> uint64_t MipsGOTParser<ELFT>::getGp() const {
   return GotSec->sh_addr + 0x7ff0;
 }