[llvm-readelf] - Introduce describe() helper functions.

[grimar]

Summary

These functions can be used to generate strings like
"SHT_?? section with index ?" to describe sections in error/warning messages,
what helps to simplify and generalize them.

Also this allows to isolate the following common code pattern:
&Sec - &cantFail(Obj->sections()).front();

[MaskRay]

Thanks!

llvm/tools/llvm-readobj/ELFDumper.cpp

3127

The previous "RELPLT" seems more specific than SHT_PROGBITS. Do we need to change it?

[jhenderson]

Just a nit from me. Otherwise LGTM.

llvm/tools/llvm-readobj/ELFDumper.cpp

382

Nit: accidental ';'

[grimar]

llvm/tools/llvm-readobj/ELFDumper.cpp

3127

So now in mips-plt.test
instead of unable to get a symbol table linked to the RELPLT section with index 2
we report unable to get a symbol table linked to the SHT_PROGBITS section with index 2

I think this change is neutral, becase it probably was not clear what is RELPLT anyways (the message could mention a section that was found at the address specified in DT_JMPREL instead and perhaps, the better name is JMPREL then.
Also, in the case of a broken object/invalid dynamic tag value, we could have something else instead of SHT_PROGBITS, so printing a section type looks useful too.

Perhaps a better mesage can be:

unable to get a symbol table linked to the SHT_PROGBITS section with index 2, found at address 0x12345 (DT_JMPREL)

llvm/test/Object/invalid.test

 Symbols:
   - Name: foo
 
 ## Check that llvm-readobj reports a warning if .dynsym has an invalid sh_entsize.
 
 # RUN: yaml2obj %s --docnum=7 -o %t7
 # RUN: llvm-readobj --dyn-symbols %t7 2>&1 | FileCheck -DFILE=%t7 --check-prefix=INVALID-DYNSYM-SIZE %s
 
-# INVALID-DYNSYM-SIZE: warning: '[[FILE]]': section with index 1 has invalid size (0x30) or entry size (0x20)
+# INVALID-DYNSYM-SIZE: warning: '[[FILE]]': SHT_DYNSYM section with index 1 has invalid size (0x30) or entry size (0x20)
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_X86_64
 Sections:

 # RELOC-BROKEN-ENTSIZE: warning: '[[FILE]]': invalid DT_RELASZ value (0x18) or DT_RELAENT value (0x19)
 
 ## Check that llvm-readobj reports a warning when .dynamic section has an invalid
 ## size, which isn't a multiple of the dynamic entry size. 
 
 # RUN: yaml2obj %s --docnum=21 -o %t21
 # RUN: llvm-readobj --dyn-relocations %t21 2>&1 | FileCheck -DFILE=%t21 --check-prefix=DYN-TABLE-SIZE %s
 
-# DYN-TABLE-SIZE: warning: '[[FILE]]': section with index 1 has invalid size (0x1){{$}}
+# DYN-TABLE-SIZE: warning: '[[FILE]]': SHT_DYNAMIC section with index 1 has invalid size (0x1){{$}}
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_EXEC
   Machine: EM_X86_64
 Sections:

llvm/test/tools/llvm-readobj/ELF/dyn-symbols.test

 DynamicSymbols: []
 
 ## Case 9: Check what we print when:
 ## a) The size of the dynamic symbol table is not a multiple of its entry size.
 # RUN: yaml2obj %s --docnum=10 -o %t10
 # RUN: llvm-readobj --dyn-symbols %t10 2>&1 | FileCheck %s -DFILE=%t10 --check-prefix=DYNSYM-SIZE-INVALID1
 # RUN: llvm-readelf --dyn-symbols %t10 2>&1 | FileCheck %s -DFILE=%t10 --check-prefix=DYNSYM-SIZE-INVALID1
 
-# DYNSYM-SIZE-INVALID1: warning: '[[FILE]]': section with index 1 has invalid size (0x1) or entry size (0x10)
+# DYNSYM-SIZE-INVALID1: warning: '[[FILE]]': SHT_DYNSYM section with index 1 has invalid size (0x1) or entry size (0x10)
 
 ## b) The same, but the DT_SYMTAB tag is present. In this case the dynamic tag has priority over the
 ##    information about a location and an entity size of the dynamic symbol table from the section header.
 ##    The code uses sizeof(Elf_Sym) for an entity size, so it can't be incorrect and
 ##    the message printed is a bit shorter.
 # RUN: yaml2obj %s --docnum=11 -o %t11
 # RUN: llvm-readobj --dyn-symbols %t11 2>&1 | FileCheck %s -DFILE=%t11 --check-prefix=DYNSYM-SIZE-INVALID2
 # RUN: llvm-readelf --dyn-symbols %t11 2>&1 | FileCheck %s -DFILE=%t11 --check-prefix=DYNSYM-SIZE-INVALID2
 
-# DYNSYM-SIZE-INVALID2: warning: '[[FILE]]': section with index 2 has invalid size (0x1){{$}}
+# DYNSYM-SIZE-INVALID2: warning: '[[FILE]]': SHT_DYNSYM section with index 2 has invalid size (0x1){{$}}
 
 ## c) In the case when the DT_SYMENT tag is present, we report when it's value does not match the
 #     value of the symbol size for the platform.
 # RUN: yaml2obj %s -D BITS=32 --docnum=12 -o %t12
 # RUN: llvm-readobj --dyn-symbols %t12 2>&1 | FileCheck %s -DFILE=%t12 --check-prefix=DYNSYM-SIZE-INVALID3
 # RUN: llvm-readelf --dyn-symbols %t12 2>&1 | FileCheck %s -DFILE=%t12 --check-prefix=DYNSYM-SIZE-INVALID3
 # RUN: yaml2obj %s -D BITS=64 --docnum=12 -o %t13
 # RUN: llvm-readobj --dyn-symbols %t13 2>&1 | FileCheck %s -DFILE=%t13 --check-prefix=DYNSYM-SIZE-INVALID4

 
 ## Check we report a warning when the entry size of the dynamic symbol table is zero.
 # RUN: yaml2obj %s --docnum=14 -o %t15
 # RUN: llvm-readobj --dyn-symbols %t15 2>&1 | FileCheck %s -DFILE=%t15 --check-prefix=DYNSYM-ZERO-ENTSIZE-LLVM
 # RUN: llvm-readelf --dyn-symbols %t15 2>&1 | \
 # RUN:   FileCheck %s -DFILE=%t15 --check-prefix=DYNSYM-ZERO-ENTSIZE-GNU --implicit-check-not="Symbol table"
 
 # DYNSYM-ZERO-ENTSIZE-LLVM:      DynamicSymbols [
-# DYNSYM-ZERO-ENTSIZE-LLVM-NEXT:  warning: '[[FILE]]': section with index 1 has invalid size (0x10) or entry size (0x0)
+# DYNSYM-ZERO-ENTSIZE-LLVM-NEXT:  warning: '[[FILE]]': SHT_DYNSYM section with index 1 has invalid size (0x10) or entry size (0x0)
 # DYNSYM-ZERO-ENTSIZE-LLVM-NEXT: ]
 
-# DYNSYM-ZERO-ENTSIZE-GNU:  warning: '[[FILE]]': section with index 1 has invalid size (0x10) or entry size (0x0)
+# DYNSYM-ZERO-ENTSIZE-GNU:  warning: '[[FILE]]': SHT_DYNSYM section with index 1 has invalid size (0x10) or entry size (0x0)
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS32
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_386
 Sections:
   - Name:    .dynsym
     Type:    SHT_DYNSYM
     EntSize: 0x0

llvm/test/tools/llvm-readobj/ELF/dynamic-malformed.test

 ## Test handling of a dynamic section size which is not a multiple of its entry size.
 ## Test the full output to demonstrate how we print the warnings.
 
 # RUN: yaml2obj %s --docnum=1 -o %t.bad-size
 # RUN: llvm-readobj --all %t.bad-size 2>&1 \
 # RUN:   | FileCheck %s -DFILE=%t.bad-size --implicit-check-not=warning: --check-prefix WARN
 # RUN: llvm-readelf --all %t.bad-size 2>&1 \
 # RUN:   | FileCheck %s -DFILE=%t.bad-size --implicit-check-not=warning: --check-prefix WARN-GNU
 
 # WARN: warning: '[[FILE]]': invalid PT_DYNAMIC size (0x4){{$}}
-# WARN: warning: '[[FILE]]': section with index 1 has invalid size (0x4){{$}}
+# WARN: warning: '[[FILE]]': SHT_DYNAMIC section with index 1 has invalid size (0x4){{$}}
 # WARN: warning: '[[FILE]]': no valid dynamic table was found
 # WARN-EMPTY:
 # WARN: File:
 # WARN: ProgramHeaders [
 # WARN: Symbols [
 # WARN: ]
 
 # WARN-GNU: warning: '[[FILE]]': invalid PT_DYNAMIC size (0x4){{$}}
-# WARN-GNU: warning: '[[FILE]]': section with index 1 has invalid size (0x4){{$}}
+# WARN-GNU: warning: '[[FILE]]': SHT_DYNAMIC section with index 1 has invalid size (0x4){{$}}
 # WARN-GNU: warning: '[[FILE]]': no valid dynamic table was found
 # WARN-GNU-NEXT: ELF Header:
 # WARN-GNU:      Symbol table '.symtab' contains 1 entries:
 # WARN-GNU:        0:
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64

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

 # 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
+# ERR6: error: '[[FILE]]': unable to get a symbol table linked to the SHT_PROGBITS 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
+# ERR7: error: '[[FILE]]': unable to get a string table for the SHT_DYNAMIC section with index 1: invalid sh_type for symbol table, expected SHT_SYMTAB or SHT_DYNSYM

llvm/tools/llvm-readobj/ELFDumper.cpp

private:
   struct VersionEntry {
     std::string Name;
     bool IsVerDef;
   };
   mutable SmallVector<Optional<VersionEntry>, 16> VersionMap;
 
   std::unordered_set<std::string> Warnings;
 
+  std::string describe(const Elf_Shdr &Sec) const;
+
 public:
   Elf_Dyn_Range dynamic_table() const {
     // A valid .dynamic section contains an array of entries terminated
     // with a DT_NULL entry. However, sometimes the section content may
     // continue past the DT_NULL entry, so to dump the section correctly,
     // we first find the end of the entries by iterating over them.
     Elf_Dyn_Range Table = DynamicTable.getAsArrayRef<Elf_Dyn>();
 
public:
   Expected<std::vector<VerNeed>>
   getVersionDependencies(const Elf_Shdr *Sec) const;
 
   template <class RelTy>
   Expected<std::pair<const Elf_Sym *, std::string>>
   getRelocationTarget(const Elf_Shdr *SymTab, const RelTy &R) const;
 
   std::function<Error(const Twine &Msg)> WarningHandler;
-  void reportUniqueWarning(Error Err) const;
+  void reportUniqueWarning(Error Err) const;;
 };
 
 template <class ELFT>
+static std::string describe(const ELFFile<ELFT> *Obj,
+                            const typename ELFT::Shdr &Sec) {
+  unsigned SecNdx = &Sec - &cantFail(Obj->sections()).front();
+  return (object::getELFSectionTypeName(Obj->getHeader()->e_machine,
+                                        Sec.sh_type) +
+          " section with index " + Twine(SecNdx))
+      .str();
+}
+
+template <class ELFT>
+std::string ELFDumper<ELFT>::describe(const Elf_Shdr &Sec) const {
+  return ::describe(ObjF->getELFFile(), Sec);
+}
+
+template <class ELFT>
 static Expected<StringRef> getLinkAsStrtab(const ELFFile<ELFT> *Obj,
-                                           const typename ELFT::Shdr *Sec,
-                                           unsigned SecNdx) {
+                                           const typename ELFT::Shdr *Sec) {
   Expected<const typename ELFT::Shdr *> StrTabSecOrErr =
       Obj->getSection(Sec->sh_link);
   if (!StrTabSecOrErr)
-    return createError("invalid section linked to " +
-                       object::getELFSectionTypeName(
-                           Obj->getHeader()->e_machine, Sec->sh_type) +
-                       " section with index " + Twine(SecNdx) + ": " +
-                       toString(StrTabSecOrErr.takeError()));
+    return createError("invalid section linked to " + describe(Obj, *Sec) +
+                       ": " + toString(StrTabSecOrErr.takeError()));
 
   Expected<StringRef> StrTabOrErr = Obj->getStringTable(*StrTabSecOrErr);
   if (!StrTabOrErr)
-    return createError("invalid string table linked to " +
-                       object::getELFSectionTypeName(
-                           Obj->getHeader()->e_machine, Sec->sh_type) +
-                       " section with index " + Twine(SecNdx) + ": " +
-                       toString(StrTabOrErr.takeError()));
+    return createError("invalid string table linked to " + describe(Obj, *Sec) +
+                       ": " + toString(StrTabOrErr.takeError()));
   return *StrTabOrErr;
 }
 
 // Returns the linked symbol table and associated string table for a given section.
 template <class ELFT>
 static Expected<std::pair<typename ELFT::SymRange, StringRef>>
 getLinkAsSymtab(const ELFFile<ELFT> *Obj, const typename ELFT::Shdr *Sec,
-                   unsigned SecNdx, unsigned ExpectedType) {
+                unsigned ExpectedType) {
   Expected<const typename ELFT::Shdr *> SymtabOrErr =
       Obj->getSection(Sec->sh_link);
   if (!SymtabOrErr)
-    return createError("invalid section linked to " +
-                       object::getELFSectionTypeName(
-                           Obj->getHeader()->e_machine, Sec->sh_type) +
-                       " section with index " + Twine(SecNdx) + ": " +
-                       toString(SymtabOrErr.takeError()));
+    return createError("invalid section linked to " + describe(Obj, *Sec) +
+                       ": " + toString(SymtabOrErr.takeError()));
 
   if ((*SymtabOrErr)->sh_type != ExpectedType)
     return createError(
-        "invalid section linked to " +
-        object::getELFSectionTypeName(Obj->getHeader()->e_machine,
-                                      Sec->sh_type) +
-        " section with index " + Twine(SecNdx) + ": expected " +
+        "invalid section linked to " + describe(Obj, *Sec) + ": expected " +
         object::getELFSectionTypeName(Obj->getHeader()->e_machine,
                                       ExpectedType) +
         ", but got " +
         object::getELFSectionTypeName(Obj->getHeader()->e_machine,
                                       (*SymtabOrErr)->sh_type));
 
-  Expected<StringRef> StrTabOrErr =
-      getLinkAsStrtab(Obj, *SymtabOrErr, Sec->sh_link);
+  Expected<StringRef> StrTabOrErr = getLinkAsStrtab(Obj, *SymtabOrErr);
   if (!StrTabOrErr)
     return createError(
         "can't get a string table for the symbol table linked to " +
-        object::getELFSectionTypeName(Obj->getHeader()->e_machine,
-                                      Sec->sh_type) +
-        " section with index " + Twine(SecNdx) + ": " +
-        toString(StrTabOrErr.takeError()));
+        describe(Obj, *Sec) + ": " + toString(StrTabOrErr.takeError()));
 
   Expected<typename ELFT::SymRange> SymsOrErr = Obj->symbols(*SymtabOrErr);
   if (!SymsOrErr)
-    return createError(
-        "unable to read symbols from the symbol table with index " +
-        Twine(Sec->sh_link) + ": " + toString(SymsOrErr.takeError()));
+    return createError("unable to read symbols from the " +
+                       describe(Obj, *Sec) + ": " +
+                       toString(SymsOrErr.takeError()));
 
   return std::make_pair(*SymsOrErr, *StrTabOrErr);
 }
 
 template <class ELFT>
 Expected<ArrayRef<typename ELFT::Versym>>
 ELFDumper<ELFT>::getVersionTable(const Elf_Shdr *Sec, ArrayRef<Elf_Sym> *SymTab,
                                  StringRef *StrTab) const {
   assert((!SymTab && !StrTab) || (SymTab && StrTab));
   const ELFFile<ELFT> *Obj = ObjF->getELFFile();
-  unsigned SecNdx = Sec - &cantFail(Obj->sections()).front();
 
   if (uintptr_t(Obj->base() + Sec->sh_offset) % sizeof(uint16_t) != 0)
-    return createError("the SHT_GNU_versym section with index " +
-                       Twine(SecNdx) + " is misaligned");
+    return createError("the " + describe(*Sec) + " is misaligned");
 
   Expected<ArrayRef<Elf_Versym>> VersionsOrErr =
       Obj->template getSectionContentsAsArray<Elf_Versym>(Sec);
   if (!VersionsOrErr)
-    return createError(
-        "cannot read content of SHT_GNU_versym section with index " +
-        Twine(SecNdx) + ": " + toString(VersionsOrErr.takeError()));
+    return createError("cannot read content of " + describe(*Sec) + ": " +
+                       toString(VersionsOrErr.takeError()));
 
   Expected<std::pair<ArrayRef<Elf_Sym>, StringRef>> SymTabOrErr =
-      getLinkAsSymtab(Obj, Sec, SecNdx, SHT_DYNSYM);
+      getLinkAsSymtab(Obj, Sec, SHT_DYNSYM);
   if (!SymTabOrErr) {
     reportUniqueWarning(SymTabOrErr.takeError());
     return *VersionsOrErr;
   }
 
   if (SymTabOrErr->first.size() != VersionsOrErr->size())
     reportUniqueWarning(
-        createError("SHT_GNU_versym section with index " + Twine(SecNdx) +
-                    ": the number of entries (" + Twine(VersionsOrErr->size()) +
+        createError(describe(*Sec) + ": the number of entries (" +
+                    Twine(VersionsOrErr->size()) +
                     ") does not match the number of symbols (" +
                     Twine(SymTabOrErr->first.size()) +
                     ") in the symbol table with index " + Twine(Sec->sh_link)));
 
   if (SymTab)
     std::tie(*SymTab, *StrTab) = *SymTabOrErr;
   return *VersionsOrErr;
 }
 
 template <class ELFT>
 Expected<std::vector<VerDef>>
 ELFDumper<ELFT>::getVersionDefinitions(const Elf_Shdr *Sec) const {
   const ELFFile<ELFT> *Obj = ObjF->getELFFile();
-  unsigned SecNdx = Sec - &cantFail(Obj->sections()).front();
 
-  Expected<StringRef> StrTabOrErr = getLinkAsStrtab(Obj, Sec, SecNdx);
+  Expected<StringRef> StrTabOrErr = getLinkAsStrtab(Obj, Sec);
   if (!StrTabOrErr)
     return StrTabOrErr.takeError();
 
   Expected<ArrayRef<uint8_t>> ContentsOrErr = Obj->getSectionContents(Sec);
   if (!ContentsOrErr)
-    return createError(
-        "cannot read content of SHT_GNU_verdef section with index " +
-        Twine(SecNdx) + ": " + toString(ContentsOrErr.takeError()));
+    return createError("cannot read content of " + describe(*Sec) + ": " +
+                       toString(ContentsOrErr.takeError()));
 
   const uint8_t *Start = ContentsOrErr->data();
   const uint8_t *End = Start + ContentsOrErr->size();
 
   auto ExtractNextAux = [&](const uint8_t *&VerdauxBuf,
                             unsigned VerDefNdx) -> Expected<VerdAux> {
     if (VerdauxBuf + sizeof(Elf_Verdaux) > End)
-      return createError("invalid SHT_GNU_verdef section with index " +
-                         Twine(SecNdx) + ": version definition " +
+      return createError("invalid " + describe(*Sec) + ": version definition " +
                          Twine(VerDefNdx) +
                          " refers to an auxiliary entry that goes past the end "
                          "of the section");
 
     auto *Verdaux = reinterpret_cast<const Elf_Verdaux *>(VerdauxBuf);
     VerdauxBuf += Verdaux->vda_next;
 
     VerdAux Aux;
     Aux.Offset = VerdauxBuf - Start;
     if (Verdaux->vda_name <= StrTabOrErr->size())
       Aux.Name = std::string(StrTabOrErr->drop_front(Verdaux->vda_name));
     else
       Aux.Name = "<invalid vda_name: " + to_string(Verdaux->vda_name) + ">";
     return Aux;
   };
 
   std::vector<VerDef> Ret;
   const uint8_t *VerdefBuf = Start;
   for (unsigned I = 1; I <= /*VerDefsNum=*/Sec->sh_info; ++I) {
     if (VerdefBuf + sizeof(Elf_Verdef) > End)
-      return createError("invalid SHT_GNU_verdef section with index " +
-                         Twine(SecNdx) + ": version definition " + Twine(I) +
-                         " goes past the end of the section");
+      return createError("invalid " + describe(*Sec) + ": version definition " +
+                         Twine(I) + " goes past the end of the section");
 
     if (uintptr_t(VerdefBuf) % sizeof(uint32_t) != 0)
       return createError(
-          "invalid SHT_GNU_verdef section with index " + Twine(SecNdx) +
+          "invalid " + describe(*Sec) +
           ": found a misaligned version definition entry at offset 0x" +
           Twine::utohexstr(VerdefBuf - Start));
 
     unsigned Version = *reinterpret_cast<const Elf_Half *>(VerdefBuf);
     if (Version != 1)
-      return createError("unable to dump SHT_GNU_verdef section with index " +
-                         Twine(SecNdx) + ": version " + Twine(Version) +
-                         " is not yet supported");
+      return createError("unable to dump " + describe(*Sec) + ": version " +
+                         Twine(Version) + " is not yet supported");
 
     const Elf_Verdef *D = reinterpret_cast<const Elf_Verdef *>(VerdefBuf);
     VerDef &VD = *Ret.emplace(Ret.end());
     VD.Offset = VerdefBuf - Start;
     VD.Version = D->vd_version;
     VD.Flags = D->vd_flags;
     VD.Ndx = D->vd_ndx;
     VD.Cnt = D->vd_cnt;
     VD.Hash = D->vd_hash;
 
     const uint8_t *VerdauxBuf = VerdefBuf + D->vd_aux;
     for (unsigned J = 0; J < D->vd_cnt; ++J) {
       if (uintptr_t(VerdauxBuf) % sizeof(uint32_t) != 0)
-        return createError("invalid SHT_GNU_verdef section with index " +
-                           Twine(SecNdx) +
+        return createError("invalid " + describe(*Sec) +
                            ": found a misaligned auxiliary entry at offset 0x" +
                            Twine::utohexstr(VerdauxBuf - Start));
 
       Expected<VerdAux> AuxOrErr = ExtractNextAux(VerdauxBuf, I);
       if (!AuxOrErr)
         return AuxOrErr.takeError();
 
       if (J == 0)
         VD.Name = AuxOrErr->Name;
       else
         VD.AuxV.push_back(*AuxOrErr);
     }
 
     VerdefBuf += D->vd_next;
   }
 
   return Ret;
 }
 
 template <class ELFT>
 Expected<std::vector<VerNeed>>
 ELFDumper<ELFT>::getVersionDependencies(const Elf_Shdr *Sec) const {
   const ELFFile<ELFT> *Obj = ObjF->getELFFile();
-  unsigned SecNdx = Sec - &cantFail(Obj->sections()).front();
-
   StringRef StrTab;
-  Expected<StringRef> StrTabOrErr = getLinkAsStrtab(Obj, Sec, SecNdx);
+  Expected<StringRef> StrTabOrErr = getLinkAsStrtab(Obj, Sec);
   if (!StrTabOrErr)
     reportUniqueWarning(StrTabOrErr.takeError());
   else
     StrTab = *StrTabOrErr;
 
   Expected<ArrayRef<uint8_t>> ContentsOrErr = Obj->getSectionContents(Sec);
   if (!ContentsOrErr)
-    return createError(
-        "cannot read content of SHT_GNU_verneed section with index " +
-        Twine(SecNdx) + ": " + toString(ContentsOrErr.takeError()));
+    return createError("cannot read content of " + describe(*Sec) + ": " +
+                       toString(ContentsOrErr.takeError()));
 
   const uint8_t *Start = ContentsOrErr->data();
   const uint8_t *End = Start + ContentsOrErr->size();
   const uint8_t *VerneedBuf = Start;
 
   std::vector<VerNeed> Ret;
   for (unsigned I = 1; I <= /*VerneedNum=*/Sec->sh_info; ++I) {
     if (VerneedBuf + sizeof(Elf_Verdef) > End)
-      return createError("invalid SHT_GNU_verneed section with index " +
-                         Twine(SecNdx) + ": version dependency " + Twine(I) +
-                         " goes past the end of the section");
+      return createError("invalid " + describe(*Sec) + ": version dependency " +
+                         Twine(I) + " goes past the end of the section");
 
     if (uintptr_t(VerneedBuf) % sizeof(uint32_t) != 0)
       return createError(
-          "invalid SHT_GNU_verneed section with index " + Twine(SecNdx) +
+          "invalid " + describe(*Sec) +
           ": found a misaligned version dependency entry at offset 0x" +
           Twine::utohexstr(VerneedBuf - Start));
 
     unsigned Version = *reinterpret_cast<const Elf_Half *>(VerneedBuf);
     if (Version != 1)
-      return createError("unable to dump SHT_GNU_verneed section with index " +
-                         Twine(SecNdx) + ": version " + Twine(Version) +
-                         " is not yet supported");
+      return createError("unable to dump " + describe(*Sec) + ": version " +
+                         Twine(Version) + " is not yet supported");
 
     const Elf_Verneed *Verneed =
         reinterpret_cast<const Elf_Verneed *>(VerneedBuf);
 
     VerNeed &VN = *Ret.emplace(Ret.end());
     VN.Version = Verneed->vn_version;
     VN.Cnt = Verneed->vn_cnt;
     VN.Offset = VerneedBuf - Start;
 
     if (Verneed->vn_file < StrTab.size())
       VN.File = std::string(StrTab.drop_front(Verneed->vn_file));
     else
       VN.File = "<corrupt vn_file: " + to_string(Verneed->vn_file) + ">";
 
     const uint8_t *VernauxBuf = VerneedBuf + Verneed->vn_aux;
     for (unsigned J = 0; J < Verneed->vn_cnt; ++J) {
       if (uintptr_t(VernauxBuf) % sizeof(uint32_t) != 0)
-        return createError("invalid SHT_GNU_verneed section with index " +
-                           Twine(SecNdx) +
+        return createError("invalid " + describe(*Sec) +
                            ": found a misaligned auxiliary entry at offset 0x" +
                            Twine::utohexstr(VernauxBuf - Start));
 
       if (VernauxBuf + sizeof(Elf_Vernaux) > End)
         return createError(
-            "invalid SHT_GNU_verneed section with index " + Twine(SecNdx) +
-            ": version dependency " + Twine(I) +
+            "invalid " + describe(*Sec) + ": version dependency " + Twine(I) +
             " refers to an auxiliary entry that goes past the end "
             "of the section");
 
       const Elf_Vernaux *Vernaux =
           reinterpret_cast<const Elf_Vernaux *>(VernauxBuf);
 
       VernAux &Aux = *VN.AuxV.emplace(VN.AuxV.end());
       Aux.Hash = Vernaux->vna_hash;
void ELFDumper<ELFT>::loadDynamicTable(const ELFFile<ELFT> *Obj) {
   // This allows us to dump dynamic sections with a broken sh_entsize
   // field.
   DynRegionInfo FromSec(ObjF->getFileName());
   bool IsSecTableValid = false;
   if (DynamicSec) {
     FromSec =
         checkDRI({ObjF->getELFFile()->base() + DynamicSec->sh_offset,
                   DynamicSec->sh_size, sizeof(Elf_Dyn), ObjF->getFileName()});
-    FromSec.Context = ("section with index " +
-                       Twine(DynamicSec - &cantFail(Obj->sections()).front()))
-                          .str();
+    FromSec.Context = describe(*DynamicSec);
     FromSec.EntSizePrintName = "";
 
     IsSecTableValid = !FromSec.getAsArrayRef<Elf_Dyn>().empty();
   }
 
   // When we only have information from one of the SHT_DYNAMIC section header or
   // PT_DYNAMIC program header, just use that.
   if (!DynamicPhdr || !DynamicSec) {
for (const Elf_Shdr &Sec : Sections) {
     switch (Sec.sh_type) {
     case ELF::SHT_SYMTAB:
       if (!DotSymtabSec)
         DotSymtabSec = &Sec;
       break;
     case ELF::SHT_DYNSYM:
       if (!DynSymRegion) {
         DynSymRegion = createDRIFrom(&Sec);
-        DynSymRegion->Context =
-            ("section with index " + Twine(&Sec - &Sections.front())).str();
+        DynSymRegion->Context = describe(Sec);
         // This is only used (if Elf_Shdr present)for naming section in GNU
         // style
         DynSymtabName =
             unwrapOrError(ObjF->getFileName(), Obj->getSectionName(&Sec));
 
         if (Expected<StringRef> E = Obj->getStringTableForSymtab(Sec))
           DynamicStringTable = *E;
         else
if (Expected<ArrayRef<uint8_t>> PltContentOrErr =
     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)) {
+          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) + ": " +
+  else
+    return createError("unable to get a symbol table linked to the " +
+                       describe(Obj, *PltRelSec) + ": " +
                        toString(PltSymTableOrErr.takeError()));
-  }
 
   if (Expected<StringRef> StrTabOrErr =
-          Obj->getStringTableForSymtab(*PltSymTable)) {
+          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()));
-  }
+  else
+    return createError("unable to get a string table for the " +
+                       describe(Obj, *PltSymTable) + ": " +
+                       toString(StrTabOrErr.takeError()));
 
   return Error::success();
 }
 
 template <class ELFT> uint64_t MipsGOTParser<ELFT>::getGp() const {
   return GotSec->sh_addr + 0x7ff0;
 }
 

 template <class ELFT>
 void GNUStyle<ELFT>::printGNUVersionSectionProlog(
     const ELFFile<ELFT> *Obj, const typename ELFT::Shdr *Sec,
     const Twine &Label, unsigned EntriesNum) {
   StringRef SecName = unwrapOrError(this->FileName, Obj->getSectionName(Sec));
   OS << Label << " section '" << SecName << "' "
      << "contains " << EntriesNum << " entries:\n";
 
-  unsigned SecNdx = Sec - &cantFail(Obj->sections()).front();
   StringRef SymTabName = "<corrupt>";
-
   Expected<const typename ELFT::Shdr *> SymTabOrErr =
       Obj->getSection(Sec->sh_link);
   if (SymTabOrErr)
     SymTabName =
         unwrapOrError(this->FileName, Obj->getSectionName(*SymTabOrErr));
   else
-    this->reportUniqueWarning(
-        createError("invalid section linked to " +
-                    object::getELFSectionTypeName(Obj->getHeader()->e_machine,
-                                                  Sec->sh_type) +
-                    " section with index " + Twine(SecNdx) + ": " +
+    this->reportUniqueWarning(createError("invalid section linked to " +
+                                          describe(Obj, *Sec) + ": " +
                                           toString(SymTabOrErr.takeError())));
 
   OS << " Addr: " << format_hex_no_prefix(Sec->sh_addr, 16)
      << "  Offset: " << format_hex(Sec->sh_offset, 8)
      << "  Link: " << Sec->sh_link << " (" << SymTabName << ")\n";
 }
 
 template <class ELFT>
 void GNUStyle<ELFT>::printVersionSymbolSection(const ELFFile<ELFT> *Obj,
if (Ndx == VER_NDX_LOCAL || Ndx == VER_NDX_GLOBAL) {
       Versions.emplace_back(Ndx == VER_NDX_LOCAL ? "*local*" : "*global*");
       continue;
     }
 
     bool IsDefault;
     Expected<StringRef> NameOrErr =
         this->dumper()->getSymbolVersionByIndex(Ndx, IsDefault);
     if (!NameOrErr) {
-      if (!NameOrErr) {
-        unsigned SecNdx = Sec - &cantFail(Obj->sections()).front();
+      if (!NameOrErr)
         this->reportUniqueWarning(createError(
-            "unable to get a version for entry " + Twine(I) +
-            " of SHT_GNU_versym section with index " + Twine(SecNdx) + ": " +
-            toString(NameOrErr.takeError())));
-      }
+            "unable to get a version for entry " + Twine(I) + " of " +
+            describe(Obj, *Sec) + ": " + toString(NameOrErr.takeError())));
       Versions.emplace_back("<corrupt>");
       continue;
     }
     Versions.emplace_back(*NameOrErr);
   }
 
   // readelf prints 4 entries per line.
   uint64_t Entries = VerTable.size();