[ELF] Define PT_ANDROID_TLS_TPOFF

[rprichard]

Summary

This segment only appears in executables. Its p_vaddr field contains the
offset (in bytes) from the architecture-specific thread pointer to the
start of a thread's copy of the executable's TLS segment. Typically, the
ELF ABI documentation for a CPU architecture specifies how this offset is
determined, but Android uses a different layout, mostly for
backwards-compatibility reasons.

The remaining segment fields are zero.

As for the specific value -- it starts with 0x66xxxxxx because GNU seems
to be using 0x64xxxxxx, and OpenBSD is using 0x65xxxxxx. I selected the
next 5 digits at random.

[rprichard]

This change isn't needed anymore -- Bionic instead uses the standard TLS layout on x86-{32,64} and arm{32,64}, but with a minimum alignment of 8 words on arm{32,64}.

include/llvm/BinaryFormat/ELF.h

enum {
 
   PT_GNU_STACK = 0x6474e551, // Indicates stack executability.
   PT_GNU_RELRO = 0x6474e552, // Read-only after relocation.
 
   PT_OPENBSD_RANDOMIZE = 0x65a3dbe6, // Fill with random data.
   PT_OPENBSD_WXNEEDED = 0x65a3dbe7,  // Program does W^X violations.
   PT_OPENBSD_BOOTDATA = 0x65a41be6,  // Section for boot arguments.
 
+  PT_ANDROID_TLS_TPOFF = 0x662df6a0, // Offset from TP to TLS segment.
+
   // ARM program header types.
   PT_ARM_ARCHEXT = 0x70000000, // Platform architecture compatibility info
   // These all contain stack unwind tables.
   PT_ARM_EXIDX = 0x70000001,
   PT_ARM_UNWIND = 0x70000001,
 
   // MIPS program header types.
   PT_MIPS_REGINFO = 0x70000000,  // Register usage information.

tools/llvm-objdump/ELFDump.cpp

case ELF::PT_OPENBSD_BOOTDATA:
       outs() << "    OPENBSD_BOOTDATA ";
       break;
     case ELF::PT_OPENBSD_RANDOMIZE:
       outs() << "    OPENBSD_RANDOMIZE ";
       break;
     case ELF::PT_OPENBSD_WXNEEDED:
       outs() << "    OPENBSD_WXNEEDED ";
       break;
+    case ELF::PT_ANDROID_TLS_TPOFF:
+      outs() << "    ANDROID_TLS_TPOFF ";
+      break;
     case ELF::PT_PHDR:
       outs() << "    PHDR ";
       break;
     case ELF::PT_TLS:
       outs() << "    TLS ";
       break;
     default:
       outs() << " UNKNOWN ";

tools/llvm-readobj/ELFDumper.cpp

static const char *getElfSegmentType(unsigned Arch, unsigned Type) {
 
   LLVM_READOBJ_ENUM_CASE(ELF, PT_GNU_STACK);
   LLVM_READOBJ_ENUM_CASE(ELF, PT_GNU_RELRO);
 
   LLVM_READOBJ_ENUM_CASE(ELF, PT_OPENBSD_RANDOMIZE);
   LLVM_READOBJ_ENUM_CASE(ELF, PT_OPENBSD_WXNEEDED);
   LLVM_READOBJ_ENUM_CASE(ELF, PT_OPENBSD_BOOTDATA);
 
+  LLVM_READOBJ_ENUM_CASE(ELF, PT_ANDROID_TLS_TPOFF);
+
   default: return "";
   }
 }
 
 static std::string getElfPtType(unsigned Arch, unsigned Type) {
   switch (Type) {
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_NULL)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_LOAD)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_DYNAMIC)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_INTERP)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_NOTE)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_SHLIB)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_PHDR)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_TLS)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_GNU_EH_FRAME)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_SUNW_UNWIND)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_GNU_STACK)
     LLVM_READOBJ_PHDR_ENUM(ELF, PT_GNU_RELRO)
+    LLVM_READOBJ_PHDR_ENUM(ELF, PT_ANDROID_TLS_TPOFF)
   default:
     // All machine specific PT_* types
     switch (Arch) {
     case ELF::EM_ARM:
       if (Type == ELF::PT_ARM_EXIDX)
         return "EXIDX";
       break;
     case ELF::EM_MIPS: