Subzero: Add basic ELFObjectWriter (text section, symtab, strtab, headers)

src/IceCfg.cpp

Index: src/IceCfg.cpp
diff --git a/src/IceCfg.cpp b/src/IceCfg.cpp
index 950a3f8ee6e9572abf6fbe4f64399264ff9d4be2..fe7db5a000cdedd7ee32862139ea78ce826db520 100644
--- a/src/IceCfg.cpp
+++ b/src/IceCfg.cpp
@@ -405,8 +405,9 @@ void Cfg::emitTextHeader(const IceString &MangledName) {
     Str << "\t.globl\t" << MangledName << "\n";
     Str << "\t.type\t" << MangledName << ",@function\n";
   }
-  Str << "\t.p2align " << getTarget()->getBundleAlignLog2Bytes() << ",0x";
-  for (AsmCodeByte I : getTarget()->getNonExecBundlePadding())
+  Assembler *Asm = getAssembler<Assembler>();
+  Str << "\t.p2align " << Asm->getBundleAlignLog2Bytes() << ",0x";
+  for (uint8_t I : Asm->getNonExecBundlePadding())
     Str.write_hex(I);
   Str << "\n";
   Str << MangledName << ":\n";
@@ -444,10 +445,19 @@ void Cfg::emitIAS() {
   TimerMarker T(TimerStack::TT_emit, this);
   assert(!Ctx->getFlags().DecorateAsm);
   IceString MangledName = getContext()->mangleName(getFunctionName());
-  emitTextHeader(MangledName);
+  if (!Ctx->getFlags().UseELFWriter)
+    emitTextHeader(MangledName);
   for (CfgNode *Node : Nodes)
     Node->emitIAS(this);
-  getAssembler<Assembler>()->emitIASBytes(Ctx);
+  // Now write the function to the file and track.
+  if (Ctx->getFlags().UseELFWriter) {
+    getAssembler<Assembler>()->alignFunction();
+    Ctx->getObjectWriter()->writeFunctionCode(
+        MangledName, getInternal(), getAssembler<Assembler>()->getBufferView());
+    // Transfer remaining fixups too. They may need their offsets adjusted.

[Jim Stichnoth, 2014/11/21 21:32:22]

Is this a TODO, or ... ?

[jvoung (off chromium), 2014/11/24 21:35:45]

Yes, a TODO and made that explicit.

Currently the ELF writer doesn't know anything about the actual target, besides
the couple of extra entries in the .defs file. So it doesn't know about
target-specific relocations. The assembler has target-specific overrides, but
then it uses the relocation enums in IceFixups.h, which are generic.

So we need to do something there. Perhaps the assembler should specify the
target-specific relocation type right away. LLVM does keep a generic-ish fixup
layer, but that might be because it has to handle ELF, Macho and Coff. I'll look
at it more.

We might also need a target hook if we want the assembler to make another pass
through and handle function calls to the same section that can be fixed w/out
waiting on the linker, and then not bother writing out those relocations.
Otherwise, we can leave it to the linker (probably just start with that).

+  } else {
+    getAssembler<Assembler>()->emitIASBytes(Ctx);
+  }
 }
 
 // Dumps the IR with an optional introductory message.