Initial Implementation of ELF

1 files changed, 125 insertions, 0 deletions

diff --git a/elf.go b/elf.go
new file mode 100755
index 0000000..ea90180
--- /dev/null
+++ b/elf.go
@@ -0,0 +1,125 @@
+package main
+
+import (
+	"encoding/binary"
+)
+
+const (
+	EI_NIDENT  = 16
+	ET_NONE    = 0
+	ET_REL     = 1
+	ET_EXEC    = 2
+	ET_DYN     = 3
+	ET_CORE    = 4
+	MIPS       = 0x08
+	EHSIZE     = 52
+	PHENSIZE   = 0x20
+	SHENTSIZE  = 0x28
+	PT_NULL    = 0
+	PT_LOAD    = 1
+	PT_DYNAMIC = 2
+	PT_INTERP  = 3
+	PT_NOTE    = 4
+	PT_SHLIB   = 5
+	PT_PHDR    = 6
+	PT_TLS     = 7
+	PF_READ    = 4
+	PF_WRITE   = 2
+	PF_EXEC    = 1
+)
+
+type ElfHeader struct {
+	e_ident     [EI_NIDENT]byte
+	e_type      uint16
+	e_machine   uint16
+	e_version   uint32
+	e_entry     uint32
+	e_phoff     uint32
+	e_shoff     uint32
+	e_flags     uint32
+	e_ehsize    uint16
+	e_phentsize uint16
+	e_phnum     uint16
+	e_shentsize uint16
+	e_shnum     uint16
+	e_shstrndx  uint16
+}
+
+type ProgramHeader struct {
+	ptype  uint32
+	offset uint32
+	vaddr  uint32
+	paddr  uint32
+	filesz uint32
+	memsz  uint32
+	flags  uint32
+	align  uint32
+}
+
+func EHInit(e_entry uint32, e_phnum uint16) ElfHeader {
+	var e ElfHeader
+	e.e_ident = [EI_NIDENT]byte{0x7f, 0x45, 0x4c, 0x46, // ELF magic number
+		0x01,                                     // 32-bit format
+		0x01,                                     // Little Endian
+		0x01,                                     // ELF Version
+		0x00,                                     // Target OS
+		0x00,                                     // Target ABI
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00} // Padding
+	e.e_type = ET_EXEC
+	e.e_machine = MIPS
+	e.e_version = 0x01
+	e.e_entry = e_entry
+	e.e_phoff = EHSIZE // Program headers will be after ELF Header
+	e.e_shoff = 0
+	e.e_ehsize = EHSIZE
+	e.e_phentsize = PHENSIZE
+	e.e_phnum = e_phnum
+	e.e_shentsize = SHENTSIZE
+	e.e_shnum = 0
+	e.e_shstrndx = 0
+	return e
+}
+
+/* NOTES: On the ToBytes methods
+ * I understand that these two methods are not the prettiest, but I need
+ * something to convert these structs to to byte arrays. From what I've read so
+ * far there seems to be no way to do this. It appears that encoding/gob
+ * ignores the size of data types, which is needed, and json serialization
+ * would not produce the proper output.
+ */
+
+func (e *ElfHeader) ToBytes() []byte {
+	bytes := make([]byte, EHSIZE)
+	i := 0
+	for _, b := range e.e_ident {
+		bytes[i] = b
+		i++
+	}
+	binary.NativeEndian.PutUint16(bytes[EI_NIDENT:], e.e_type)
+	binary.NativeEndian.PutUint16(bytes[18:], e.e_machine)
+	binary.NativeEndian.PutUint32(bytes[20:], e.e_version)
+	binary.NativeEndian.PutUint32(bytes[24:], e.e_entry)
+	binary.NativeEndian.PutUint32(bytes[28:], e.e_phoff)
+	binary.NativeEndian.PutUint32(bytes[32:], e.e_shoff)
+	binary.NativeEndian.PutUint32(bytes[36:], e.e_flags)
+	binary.NativeEndian.PutUint16(bytes[40:], e.e_ehsize)
+	binary.NativeEndian.PutUint16(bytes[42:], e.e_phentsize)
+	binary.NativeEndian.PutUint16(bytes[44:], e.e_phnum)
+	binary.NativeEndian.PutUint16(bytes[46:], e.e_shentsize)
+	binary.NativeEndian.PutUint16(bytes[48:], e.e_shnum)
+	binary.NativeEndian.PutUint16(bytes[50:], e.e_shstrndx)
+	return bytes
+}
+
+func (p *ProgramHeader) ToBytes() []byte {
+	bytes := make([]byte, PHENSIZE)
+	binary.NativeEndian.PutUint32(bytes[0:], p.ptype)
+	binary.NativeEndian.PutUint32(bytes[4:], p.offset)
+	binary.NativeEndian.PutUint32(bytes[8:], p.vaddr)
+	binary.NativeEndian.PutUint32(bytes[12:], p.paddr)
+	binary.NativeEndian.PutUint32(bytes[16:], p.filesz)
+	binary.NativeEndian.PutUint32(bytes[20:], p.memsz)
+	binary.NativeEndian.PutUint32(bytes[24:], p.flags)
+	binary.NativeEndian.PutUint32(bytes[28:], p.align)
+	return bytes
+}