iniital checkin of ELFWriter header.

For now, the elf writer is only capable of emitting an empty elf file, with
a section table and a section table string table.  This will be enhanced
in the future :)

llvm-svn: 22290

include/llvm/CodeGen/ELFWriter.h

@@ -0,0 +1,174 @@
+//===-- ELFWriter.h - Target-independent ELF writer support -----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file defines the ELFWriter class.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_ELFWRITER_H
+#define LLVM_CODEGEN_ELFWRITER_H
+
+#include "llvm/CodeGen/MachineFunctionPass.h"
+
+namespace llvm {
+  class GlobalVariable;
+
+  /// ELFWriter - This class implements the common target-independent code for
+  /// writing ELF files.  Targets should derive a class from this to
+  /// parameterize the output format.
+  ///
+  class ELFWriter : public MachineFunctionPass {
+  protected:
+    ELFWriter(std::ostream &O, TargetMachine &TM);
+
+    /// Output stream to send the resultant object file to.
+    ///
+    std::ostream &O;
+
+    /// Target machine description.
+    ///
+    TargetMachine &TM;
+
+    //===------------------------------------------------------------------===//
+    // Properties to be set by the derived class ctor, used to configure the
+    // ELFWriter.
+
+    // e_machine - This field is the target specific value to emit as the
+    // e_machine member of the ELF header.
+    unsigned short e_machine;
+
+    // e_flags - The machine flags for the target.  This defaults to zero.
+    unsigned e_flags;
+
+    //===------------------------------------------------------------------===//
+    // Properties inferred automatically from the target machine.
+    //
+
+    /// is64Bit/isLittleEndian - This information is inferred from the target
+    /// machine directly, indicating whether to emit a 32- or 64-bit ELF file.
+    bool is64Bit, isLittleEndian;
+
+    /// doInitialization - Emit the file header and all of the global variables
+    /// for the module to the ELF file.
+    bool doInitialization(Module &M);
+
+    bool runOnMachineFunction(MachineFunction &MF);
+
+
+    /// doFinalization - Now that the module has been completely processed, emit
+    /// the ELF file to 'O'.
+    bool doFinalization(Module &M);
+
+  private:
+    // The buffer we are accumulating the file into.  Note that this should be
+    // changed into something much more efficient later (and the bytecode writer
+    // as well!).
+    std::vector<unsigned char> OutputBuffer;
+
+    /// ELFSection - This struct contains information about each section that is
+    /// emitted to the OutputBuffer.  This is eventually turned into the section
+    /// header table at the end of the file.
+    struct ELFSection {
+      std::string Name;       // Name of the section.
+      unsigned NameIdx;       // Index in .shstrtab of name, once emitted.
+      unsigned Type;
+      unsigned Flags;
+      uint64_t Addr;
+      unsigned Offset;
+      unsigned Size;
+      unsigned Link;
+      unsigned Info;
+      unsigned Align;
+      unsigned EntSize;
+      ELFSection() : Type(0), Flags(0), Addr(0), Offset(0), Size(0), Link(0),
+                     Info(0), Align(0), EntSize(0) {
+      }
+      ELFSection(const char *name, unsigned offset)
+        : Name(name), Type(0), Flags(0), Addr(0), Offset(offset), Size(0),
+          Link(0), Info(0), Align(0), EntSize(0) {
+      }
+    };
+
+    /// SectionList - This is the list of sections that we have emitted to the
+    /// file.  Once the file has been completely built, the section header table
+    /// is constructed from this info.
+    std::vector<ELFSection> SectionList;
+
+    // As we accumulate the ELF file into OutputBuffer, we occasionally need to
+    // keep track of locations to update later (e.g. the location of the section
+    // table in the ELF header.  These members keep track of the offset in
+    // OffsetBuffer of these various pieces to update and other locations in the
+    // file.
+    unsigned ELFHeader_e_shoff_Offset;     // e_shoff    in ELF header.
+    unsigned ELFHeader_e_shstrndx_Offset;  // e_shstrndx in ELF header.
+    unsigned ELFHeader_e_shnum_Offset;     // e_shnum    in ELF header.
+
+    void outbyte(unsigned char X) { OutputBuffer.push_back(X); }
+    void outhalf(unsigned short X) {
+      if (isLittleEndian) {
+        OutputBuffer.push_back(X&255);
+        OutputBuffer.push_back(X >> 8);
+      } else {
+        OutputBuffer.push_back(X >> 8);
+        OutputBuffer.push_back(X&255);
+      }
+    }
+    void outword(unsigned X) {
+      if (isLittleEndian) {
+        OutputBuffer.push_back((X >>  0) & 255);
+        OutputBuffer.push_back((X >>  8) & 255);
+        OutputBuffer.push_back((X >> 16) & 255);
+        OutputBuffer.push_back((X >> 24) & 255);
+      } else {
+        OutputBuffer.push_back((X >> 24) & 255);
+        OutputBuffer.push_back((X >> 16) & 255);
+        OutputBuffer.push_back((X >>  8) & 255);
+        OutputBuffer.push_back((X >>  0) & 255);
+      }
+    }
+    void outaddr(uint64_t X) {
+      if (!is64Bit)
+        outword((unsigned)X);
+      else
+        assert(0 && "Emission of 64-bit data not implemented yet!");
+    }
+
+    // fix functions - Replace an existing entry at an offset.
+    void fixhalf(unsigned short X, unsigned Offset) {
+      unsigned char *P = &OutputBuffer[Offset];
+      P[0] = (X >> (isLittleEndian ?  0 : 8)) & 255;
+      P[1] = (X >> (isLittleEndian ?  8 : 0)) & 255;
+    }
+
+    void fixword(unsigned X, unsigned Offset) {
+      unsigned char *P = &OutputBuffer[Offset];
+      P[0] = (X >> (isLittleEndian ?  0 : 24)) & 255;
+      P[1] = (X >> (isLittleEndian ?  8 : 16)) & 255;
+      P[2] = (X >> (isLittleEndian ? 16 :  8)) & 255;
+      P[3] = (X >> (isLittleEndian ? 24 :  0)) & 255;
+    }
+
+    void fixaddr(uint64_t X, unsigned Offset) {
+      if (!is64Bit)
+        fixword((unsigned)X, Offset);
+      else
+        assert(0 && "Emission of 64-bit data not implemented yet!");
+    }
+
+  private:
+    void EmitDATASectionGlobal(GlobalVariable *GV);
+    void EmitBSSSectionGlobal(GlobalVariable *GV);
+    void EmitGlobal(GlobalVariable *GV);
+
+    void EmitSectionTableStringTable();
+    void EmitSectionTable();
+  };
+}
+
+#endif