[x32] Add X32 backend

[pavel.v.chupin]

Summary

This is minimal change for backend required to have "hello world" compiled
and working on x32 target (x86_64-linux-gnux32). More patches for x32 will
follow.
Note that this patch for clang is also required:
http://reviews.llvm.org/D4180

[jfb]

Sorry, I'm missing a bit of context for this patch. Could you explain in the commit message why this is the right thing to do?

[pavel.v.chupin]

Updating the commit message.

[dschuff]

The code looks OK to me, although the commit message should say what it actually does (i.e., add an AsmBackend for X32 which uses ELF32 with x86_64).

This is very minimal though; do you have a more complete set of patches available for X32 so we can see the bigger picture of where this is going?

[pavel.v.chupin]

Updating commit title

[pavel.v.chupin]

This is very minimal indeed.
I've got more raw changes, but want to split them first and polish for better review. Also working on tests.
I'm going to submit next patch very soon.

[pavel.v.chupin]

Is it OK to commit?

[dschuff]

This patch is fine (in my opinion) to commit, but before we get too far into landing more stuff, I would really like to see a sort of roadmap, e.g. what are the major data structures what will need to be changed, etc. Even if it's just a raw patch dump somewhere.

Also I might be interested in trying this out myself, what would I need to be able to do that? Just a distro with x32 libs?

[pavel.v.chupin]

Thanks for comments.
I'll open new thread at llvmdev and provide some sort of roadmap and list of changes required.

In D4181#20, @dschuff wrote:

Also I might be interested in trying this out myself, what would I need to be able to do that? Just a distro with x32 libs?

Yes. You need kernel and libs supporting x32. Ubuntu 14 has x32 packages available to try.

[zinovy.nis]

Closed by commit rL212716 (authored by @zinovy.nis).

lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

public:
   ELFX86_32AsmBackend(const Target &T, uint8_t OSABI, StringRef CPU)
     : ELFX86AsmBackend(T, OSABI, CPU) {}
 
   MCObjectWriter *createObjectWriter(raw_ostream &OS) const override {
     return createX86ELFObjectWriter(OS, /*IsELF64*/ false, OSABI, ELF::EM_386);
   }
 };
 
+class ELFX86_X32AsmBackend : public ELFX86AsmBackend {
+public:
+  ELFX86_X32AsmBackend(const Target &T, uint8_t OSABI, StringRef CPU)
+      : ELFX86AsmBackend(T, OSABI, CPU) {}
+
+  MCObjectWriter *createObjectWriter(raw_ostream &OS) const override {
+    return createX86ELFObjectWriter(OS, /*IsELF64*/ false, OSABI,
+                                    ELF::EM_X86_64);
+  }
+};
+
 class ELFX86_64AsmBackend : public ELFX86AsmBackend {
 public:
   ELFX86_64AsmBackend(const Target &T, uint8_t OSABI, StringRef CPU)
     : ELFX86AsmBackend(T, OSABI, CPU) {}
 
   MCObjectWriter *createObjectWriter(raw_ostream &OS) const override {
     return createX86ELFObjectWriter(OS, /*IsELF64*/ true, OSABI, ELF::EM_X86_64);
   }
MachO::CPUSubTypeX86 CS =
             .Default(MachO::CPU_SUBTYPE_X86_64_ALL);
     return new DarwinX86_64AsmBackend(T, MRI, CPU, CS);
   }
 
   if (TheTriple.isOSWindows() && !TheTriple.isOSBinFormatELF())
     return new WindowsX86AsmBackend(T, true, CPU);
 
   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
+
+  if (TheTriple.getEnvironment() == Triple::GNUX32)
+    return new ELFX86_X32AsmBackend(T, OSABI, CPU);
   return new ELFX86_64AsmBackend(T, OSABI, CPU);
 }