Add a function to get the segment name of a section.

On MachO, sections also have segment names. When a tool looking at a .o file
prints a segment name, this is what they mean. In reality, a .o has only one
anonymous, segment.

This patch adds a MachO only function to fetch that segment name. I named it
getSectionFinalSegmentName since the main use for the name seems to be inform
the linker with segment this section should go to.

The patch also changes MachOObjectFile::getSectionName to return just the
section name instead of computing SegmentName,SectionName.

The main difference from the previous patch is that it doesn't use
InMemoryStruct. It is extremely dangerous: if the endians match it returns
a pointer to the file buffer, if not, it returns a pointer to an internal buffer
that is overwritten in the next API call.

We should change all of this code to use
support::detail::packed_endian_specific_integral like ELF, but since these
functions only handle strings, they work with big and little endian machines
as is.

I have tested this by installing ubuntu 12.10 ppc on qemu, that is why it took
so long :-)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@170838 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-objdump/MachODump.cpp

@@ -334,9 +334,15 @@ void llvm::DisassembleInputMachO(StringRef Filename) {
   for (unsigned SectIdx = 0; SectIdx != Sections.size(); SectIdx++) {
     StringRef SectName;
     if (Sections[SectIdx].getName(SectName) ||
-        SectName.compare("__TEXT,__text"))
+        SectName != "__text")
       continue; // Skip non-text sections
 
+    StringRef SegmentName;
+    DataRefImpl DR = Sections[SectIdx].getRawDataRefImpl();
+    if (MachOOF->getSectionFinalSegmentName(DR, SegmentName) ||
+        SegmentName != "__TEXT")
+      continue;
+
     // Insert the functions from the function starts segment into our map.
     uint64_t VMAddr;
     Sections[SectIdx].getAddress(VMAddr);