[llvm-readelf] - Don't print OS/Processor specific prefix for known ELF file types.

[grimar]

Summary

This is a change suggested in post commit comments for
D93096 (https://reviews.llvm.org/D93096#2451796).

Imagine we want to add a custom OS specific ELF file type.
For that we can update the ElfObjectFileType array:

static const EnumEntry<unsigned> ElfObjectFileType[] = {
...
  {"Core",         "CORE (Core file)",         ELF::ET_CORE},
  {"MyType",       "MyType (my description)",     0xfe01},
};

The current code then might print:

OS Specific: (MyType (my description))

Though instead we probably would like to see a nicer output, e.g:

Type: MyType (my description)

To achieve that we can reorder the code slightly.

It is impossible to add a test I think, because we have no custom values in
the ElfObjectFileType array in LLVM.

[jhenderson]

Obviously, this looks good to me, since this was my original suggestion, but it's probably best for @MaskRay or others to agree.

[MaskRay]

This is certainly fine:) Known ElfObjectFileType values can be handled first. Good to know there are indeed OS-specific ET_* in use)

llvm/tools/llvm-readobj/ELFDumper.cpp

if (e.e_version == ELF::EV_CURRENT)
     OS << " (current)";
   OS << "\n";
   Str = printEnum(e.e_ident[ELF::EI_OSABI], makeArrayRef(ElfOSABI));
   printFields(OS, "OS/ABI:", Str);
   printFields(OS,
               "ABI Version:", std::to_string(e.e_ident[ELF::EI_ABIVERSION]));
 
   Str = printEnum(e.e_type, makeArrayRef(ElfObjectFileType));
-  if (e.e_type >= ET_LOPROC) {
+  if (makeArrayRef(ElfObjectFileType).end() ==
+      llvm::find_if(ElfObjectFileType, [&](const EnumEntry<unsigned> &E) {
+        return E.Value == e.e_type;
+      })) {
+    if (e.e_type >= ET_LOPROC)
       Str = "Processor Specific: (" + Str + ")";
-  } else if (e.e_type >= ET_LOOS) {
+    else if (e.e_type >= ET_LOOS)
       Str = "OS Specific: (" + Str + ")";
-  } else if (makeArrayRef(ElfObjectFileType).end() ==
-             llvm::find_if(ElfObjectFileType,
-                           [&](const EnumEntry<unsigned> &E) {
-                             return E.Value == e.e_type;
-                           }))
+    else
       Str = "<unknown>: " + Str;
+  }
   printFields(OS, "Type:", Str);
 
   Str = printEnum(e.e_machine, makeArrayRef(ElfMachineType));
   printFields(OS, "Machine:", Str);
   Str = "0x" + to_hexString(e.e_version);
   printFields(OS, "Version:", Str);
   Str = "0x" + to_hexString(e.e_entry);
   printFields(OS, "Entry point address:", Str);