Implemented basic data access

This commit is contained in:
Eduard Urbach 2023-10-18 17:03:31 +02:00
parent 8b66c9588c
commit 506d1e30bf
Signed by: akyoto
GPG Key ID: C874F672B1AF20C0
4 changed files with 36 additions and 15 deletions

View File

@ -38,9 +38,17 @@ func New(directory string) (*Build, error) {
func (build *Build) Run() error {
if build.WriteExecutable {
sampleCode := []byte{
0xb8, 0x3c, 0x00, 0x00, 0x00, // mov rax, 60
0xbf, 0x00, 0x00, 0x00, 0x00, // mov rdi, 0
0xb8, 0x01, 0x00, 0x00, 0x00, // mov eax, 1
0xbf, 0x01, 0x00, 0x00, 0x00, // mov edi, 1
0xbe, 0x80 + 0x22, 0x00, 0x40, 0x00, // mov esi, 0x4000A2
0xba, 0x06, 0x00, 0x00, 0x00, // mov edx, 6
0x0f, 0x05, // syscall
0xb8, 0x3c, 0x00, 0x00, 0x00, // mov eax, 60
0xbf, 0x00, 0x00, 0x00, 0x00, // mov edi, 0
0x0f, 0x05, // syscall
'H', 'e', 'l', 'l', 'o', '\n',
}
return writeToDisk(build.ExecutablePath, sampleCode, nil)

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@ -4,8 +4,9 @@ const (
LittleEndian = 1
TypeExecutable = 2
ArchitectureAMD64 = 0x3E
Align = 16
HeaderSize = 64
CacheLineSize = 64
Align = CacheLineSize
)
// Header contains general information.

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@ -6,14 +6,13 @@ import (
)
const (
baseAddress = 0x10000
baseAddress = 0x400000
)
// ELF64 represents an ELF 64-bit file.
type ELF64 struct {
Header
ProgramHeader
Padding []byte
Code []byte
}
@ -43,7 +42,7 @@ func New(code []byte) *ELF64 {
},
ProgramHeader: ProgramHeader{
Type: ProgramTypeLOAD,
Flags: ProgramFlagsExecutable,
Flags: ProgramFlagsExecutable | ProgramFlagsReadable,
Offset: 0x80,
VirtualAddress: baseAddress + 0x80,
PhysicalAddress: baseAddress + 0x80,
@ -51,7 +50,6 @@ func New(code []byte) *ELF64 {
SizeInMemory: int64(len(code)),
Align: Align,
},
Padding: []byte{0, 0, 0, 0, 0, 0, 0, 0},
Code: code,
}
@ -62,6 +60,6 @@ func New(code []byte) *ELF64 {
func (elf *ELF64) Write(writer io.Writer) {
binary.Write(writer, binary.LittleEndian, &elf.Header)
binary.Write(writer, binary.LittleEndian, &elf.ProgramHeader)
writer.Write(elf.Padding)
writer.Write([]byte{0, 0, 0, 0, 0, 0, 0, 0})
writer.Write(elf.Code)
}

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@ -1,12 +1,26 @@
# ELF
## File contents
## Basic structure
- ELF header
- Program headers
- Sections
- Section headers
1. ELF header (0x00 - 0x40)
2. Program header (0x40 - 0x78)
3. Padding (0x78 - 0x80)
4. Machine code (0x80)
## Entry point
The entry point is defined in the first 64 bytes (ELF header).
## Base address
The minimum base address is controlled by the `mmap` settings:
```shell
sysctl vm.mmap_min_addr
```
Usually, this value is 65536 (0x1000).
## Initialization in Linux
See `/lib/modules/$(uname -r)/build/arch/x86/include/asm/elf.h`.