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

src/IceELFObjectWriter.h

Index: src/IceELFObjectWriter.h
diff --git a/src/IceELFObjectWriter.h b/src/IceELFObjectWriter.h
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+++ b/src/IceELFObjectWriter.h
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+//===- subzero/src/IceELFObjectWriter.h - ELF object writer -----*- C++ -*-===//
+//
+//                        The Subzero Code Generator
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Abstraction for a writer that is responsible for writing an ELF file.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SUBZERO_SRC_ICEELFOBJECTWRITER_H
+#define SUBZERO_SRC_ICEELFOBJECTWRITER_H
+
+#include "IceDefs.h"
+#include "IceELFSection.h"
+#include "IceELFStreamer.h"
+
+using namespace llvm::ELF;
+
+namespace Ice {
+
+// Higher level ELF object writer.  Manages section information and writes
+// the final ELF object.  The object writer will write to file the code
+// and data as it is being defined (rather than keep a copy).
+// After all definitions are written out, it will finalize the bookkeeping
+// sectinos and write them out.  Expected usage:

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

sections

[jvoung (off chromium), 2014/11/24 21:35:46]

Done.

+//
+// (1) writeInitialELFHeader
+// (2) writeDataInitializer*
+// (3) writeFunctionCode*
+// (4) writeNonUserSections
+class ELFObjectWriter {
+  ELFObjectWriter(const ELFObjectWriter &) = delete;
+  ELFObjectWriter &operator=(const ELFObjectWriter &) = delete;
+
+public:
+  ELFObjectWriter(GlobalContext &Ctx, ELFStreamer &Out);
+
+  // Write the initial ELF header. This is just to reserve space in the ELF
+  // file. Reserving space allows the other functions to write text
+  // and data directly to the file and get the right file offsets.
+  void writeInitialELFHeader();
+
+  // Copy final (non-resizeable) data of functions' text section to file.
+  // TODO(jvoung): This also needs the relocations to adjust the
+  // section-relative offsets and hook them up to the symbol table references.
+  void writeFunctionCode(const IceString &FuncName, bool IsInternal,
+                         const llvm::StringRef Data);
+
+  // Add way to write/copy data symbols / set initializers.

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

This comment line sounds more like part of the TODO than documenting the method?

[jvoung (off chromium), 2014/11/24 21:35:46]

Done.

+  // TODO(jvoung): This needs to know which section.
+  // This also needs the relocations to hook them up to the symbol table
+  // references.
+  void writeDataInitializer(const IceString &VarName,
+                            const llvm::StringRef Data);
+
+  // Do final layout and write out the rest of the object file, then
+  // patch up the initial ELF header with the final info.
+  void writeNonUserSections();
+
+private:
+  GlobalContext &Ctx;
+  ELFStreamer &Str;
+  bool SectionNumbersAssigned;
+
+  // All created sections, separated into different pools.
+  typedef std::vector<ELFSection *> SectionList;
+  typedef std::vector<ELFTextSection *> TextSectionList;
+  typedef std::vector<ELFDataSection *> DataSectionList;
+  typedef std::vector<ELFRelocationSectionBase *> RelSectionList;
+  TextSectionList TextSections;
+  RelSectionList RelTextSections;
+  DataSectionList DataSections;
+  RelSectionList RelDataSections;
+  DataSectionList RoDataSections;
+  RelSectionList RelRoDataSections;
+
+  // Handles to special sections that need incremental bookkeeping.
+  ELFSection *NullSection;
+  ELFStringTableSection *ShStrTab;
+  ELFSymbolTableSection *SymTab;
+  ELFStringTableSection *StrTab;
+
+  template <typename T>
+  T *createSection(const IceString &Name, Elf64_Word sh_type,

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

Capitalize arg names

(hmm, on second thought I see these args are supposed to mimic LLVM field names,
so I guess it's OK...)

[jvoung (off chromium), 2014/11/24 21:35:46]

Hmm, I'll just go ahead and capitalize them. There's also some local vars like
"SymTabEntSize".

+                   Elf64_Xword sh_flags, Elf64_Xword sh_addralign,
+                   Elf64_Xword sh_entsize);
+
+  // Align the file position before writing out a section's data,
+  // and return the position of the file.
+  Elf64_Off alignFileOffset(Elf64_Xword Align);
+
+  // Assign an ordering / section numbers to each section.
+  // Fill in other information that is only known near the end
+  // (such as the size, if it wasn't already incrementally updated),

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

end sentence with period

[jvoung (off chromium), 2014/11/24 21:35:46]

Done.

+  // Then put them all in one vector for conveniently writing out
+  // all of the section headers.
+  void assignSectionNumbersInfo(SectionList &AllSections);
+
+  // This function assigns .foo and .rel.foo consecutive section numbers.
+  // It also sets the relocation section's sh_info field to the related
+  // section's number.
+  template <typename UserSectionList>
+  void assignRelSectionNumInPairs(SizeT &CurSectionNumber,
+                                  UserSectionList &UserSections,
+                                  RelSectionList &RelSections,
+                                  SectionList &AllSections);
+
+  // Link the relocation sections to the symbol table.
+  void assignRelLinkNum(SizeT SymTabNumber, RelSectionList &RelSections);
+
+  // Write the ELF file header with the given information about sections.
+  template <bool IsELF64>
+  void writeELFHeaderInternal(uint64_t SectionHeaderOffset,
+                              SizeT SectHeaderStrIndex, SizeT NumSections);
+};
+
+} // end of namespace Ice
+
+#endif // SUBZERO_SRC_ICEELFOBJECTWRITER_H