[llvm-readobj] Display sections that do not belong to a segment in the section-mapping

Summary:
The following patch adds the "None" line to the section to segment mapping dump.
That line lists the sections that do not belong to any segment.
I realize that this change differs from GNU readelf which does not display the latter information.

I'd rather not add this "feature" under a command line option.  I think that might introduce confusion, since users would have to
make an additional decision as to if they want to see all of the section-to-segment map or just a subset of it.

Another option is to only print the "None" line if the `--section-mapping` option is passed; however,
that might also introduce some confusion, because the section-to-segment map would be different between`--program-headers`
and the `--section-mapping` output.  While the difference is just the "None" line, it seems that if we choose to display
the segment-to-section mapping, then we should always display the whole map including the sections
that do not belong to segments.

```
Section to Segment mapping:
  Segment Sections...
   00
   01     .interp
   02     .interp .note.ABI-tag .gnu.hash
   03     .init_array .fini_array .dynamic
   04     .dynamic
   05     .note.ABI-tag
   06     .eh_frame_hdr
   07
   08     .init_array .fini_array .dynamic .got
   None   .comment .symtab .strtab .shstrtab <--- THIS LINE
```

Reviewers: grimar, rupprecht, jhenderson, espindola

Reviewed By: rupprecht

Subscribers: khemant, emaste, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D57700

llvm-svn: 353217

1 files changed, 16 insertions, 1 deletions

diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index 1757fd6cce5..2c9b159575b 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -19,6 +19,7 @@
 #include "llvm-readobj.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/STLExtras.h"
@@ -3316,6 +3317,7 @@ void GNUStyle<ELFT>::printProgramHeaders(const ELFO *Obj) {
 template <class ELFT>
 void GNUStyle<ELFT>::printSectionMapping(const ELFO *Obj) {
   OS << "\n Section to Segment mapping:\n  Segment Sections...\n";
+  DenseSet<const Elf_Shdr *> BelongsToSegment;
   int Phnum = 0;
   for (const Elf_Phdr &Phdr : unwrapOrError(Obj->program_headers())) {
     std::string Sections;
@@ -3330,12 +3332,25 @@ void GNUStyle<ELFT>::printSectionMapping(const ELFO *Obj) {
                           Phdr.p_type != ELF::PT_TLS;
       if (!TbssInNonTLS && checkTLSSections(Phdr, Sec) &&
           checkoffsets(Phdr, Sec) && checkVMA(Phdr, Sec) &&
-          checkPTDynamic(Phdr, Sec) && (Sec.sh_type != ELF::SHT_NULL))
+          checkPTDynamic(Phdr, Sec) && (Sec.sh_type != ELF::SHT_NULL)) {
         Sections += unwrapOrError(Obj->getSectionName(&Sec)).str() + " ";
+        BelongsToSegment.insert(&Sec);
+      }
     }
     OS << Sections << "\n";
     OS.flush();
   }
+
+  // Display sections that do not belong to a segment.
+  std::string Sections;
+  for (const Elf_Shdr &Sec : unwrapOrError(Obj->sections())) {
+    if (BelongsToSegment.find(&Sec) == BelongsToSegment.end())
+      Sections += unwrapOrError(Obj->getSectionName(&Sec)).str() + ' ';
+  }
+  if (!Sections.empty()) {
+    OS << "   None  " << Sections << '\n';
+    OS.flush();
+  }
 }
 
 template <class ELFT>