Implemented basic data access
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8b66c9588c
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@ -38,9 +38,17 @@ func New(directory string) (*Build, error) {
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func (build *Build) Run() error {
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if build.WriteExecutable {
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sampleCode := []byte{
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0xb8, 0x3c, 0x00, 0x00, 0x00, // mov rax, 60
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0xbf, 0x00, 0x00, 0x00, 0x00, // mov rdi, 0
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0xb8, 0x01, 0x00, 0x00, 0x00, // mov eax, 1
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0xbf, 0x01, 0x00, 0x00, 0x00, // mov edi, 1
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0xbe, 0x80 + 0x22, 0x00, 0x40, 0x00, // mov esi, 0x4000A2
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0xba, 0x06, 0x00, 0x00, 0x00, // mov edx, 6
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0x0f, 0x05, // syscall
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0xb8, 0x3c, 0x00, 0x00, 0x00, // mov eax, 60
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0xbf, 0x00, 0x00, 0x00, 0x00, // mov edi, 0
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0x0f, 0x05, // syscall
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'H', 'e', 'l', 'l', 'o', '\n',
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}
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return writeToDisk(build.ExecutablePath, sampleCode, nil)
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@ -4,8 +4,9 @@ const (
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LittleEndian = 1
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TypeExecutable = 2
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ArchitectureAMD64 = 0x3E
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Align = 16
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HeaderSize = 64
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CacheLineSize = 64
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Align = CacheLineSize
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)
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// Header contains general information.
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@ -6,15 +6,14 @@ import (
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)
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const (
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baseAddress = 0x10000
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baseAddress = 0x400000
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)
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// ELF64 represents an ELF 64-bit file.
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type ELF64 struct {
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Header
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ProgramHeader
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Padding []byte
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Code []byte
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Code []byte
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}
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// New creates a new 64-bit ELF binary.
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@ -43,7 +42,7 @@ func New(code []byte) *ELF64 {
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},
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ProgramHeader: ProgramHeader{
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Type: ProgramTypeLOAD,
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Flags: ProgramFlagsExecutable,
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Flags: ProgramFlagsExecutable | ProgramFlagsReadable,
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Offset: 0x80,
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VirtualAddress: baseAddress + 0x80,
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PhysicalAddress: baseAddress + 0x80,
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@ -51,8 +50,7 @@ func New(code []byte) *ELF64 {
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SizeInMemory: int64(len(code)),
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Align: Align,
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},
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Padding: []byte{0, 0, 0, 0, 0, 0, 0, 0},
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Code: code,
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Code: code,
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}
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return elf
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@ -62,6 +60,6 @@ func New(code []byte) *ELF64 {
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func (elf *ELF64) Write(writer io.Writer) {
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binary.Write(writer, binary.LittleEndian, &elf.Header)
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binary.Write(writer, binary.LittleEndian, &elf.ProgramHeader)
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writer.Write(elf.Padding)
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writer.Write([]byte{0, 0, 0, 0, 0, 0, 0, 0})
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writer.Write(elf.Code)
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}
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@ -1,12 +1,26 @@
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# ELF
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## File contents
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## Basic structure
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- ELF header
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- Program headers
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- Sections
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- Section headers
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1. ELF header (0x00 - 0x40)
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2. Program header (0x40 - 0x78)
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3. Padding (0x78 - 0x80)
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4. Machine code (0x80)
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## Entry point
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The entry point is defined in the first 64 bytes (ELF header).
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## Base address
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The minimum base address is controlled by the `mmap` settings:
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```shell
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sysctl vm.mmap_min_addr
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```
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Usually, this value is 65536 (0x1000).
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## Initialization in Linux
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See `/lib/modules/$(uname -r)/build/arch/x86/include/asm/elf.h`.
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