114 lines
2.9 KiB
V
114 lines
2.9 KiB
V
// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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module x64
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import os
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const (
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mag0 = byte(0x7f)
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mag1 = `E`
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mag2 = `L`
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mag3 = `F`
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ei_class = 4
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elfclass64 = 2
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elfdata2lsb = 1
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ev_current = 1
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)
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// ELF file types
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const (
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elf_osabi = 0
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et_rel = 1
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et_exec = 2
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et_dyn = 3
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e_machine = 0x3e
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shn_xindex = 0xffff
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sht_null = 0
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)
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const (
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segment_start = 0x400000
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placeholder = 0
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sevens = 0x77777777
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)
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pub fn (mut g Gen) generate_elf_header() {
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g.buf << [byte(mag0),
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mag1,
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mag2,
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mag3
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]
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g.buf << elfclass64 // file class
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g.buf << elfdata2lsb // data encoding
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g.buf << ev_current // file version
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g.buf << 1 // elf_osabi
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g.write64(0) // et_rel) // et_rel for .o
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g.write16(2) // e_type
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g.write16(e_machine) //
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g.write32(ev_current) // e_version
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eh_size := 0x40
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phent_size := 0x38
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g.write64(segment_start + eh_size + phent_size) // e_entry
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g.write64(0x40) // e_phoff
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g.write64(0) // e_shoff
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g.write32(0) // e_flags
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g.write16(eh_size) // e_ehsize
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g.write16(phent_size) // e_phentsize
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g.write16(1) // e_phnum
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g.write16(0) // e_shentsize
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g.write16(0) // e_shnum (number of sections)
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g.write16(0) // e_shstrndx
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// Elf64_Phdr
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g.write32(1) // p_type
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g.write32(5) // p_flags
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g.write64(0) // p_offset
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g.write64(segment_start) // p_vaddr addr:050
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g.write64(segment_start) //
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g.file_size_pos = g.buf.len
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g.write64(0) // p_filesz PLACEHOLDER, set to file_size later // addr: 060
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g.write64(0) // p_memsz
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g.write64(0x1000) // p_align
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// user code starts here at
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// address: 00070 and a half
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println('code_start_pos = $g.buf.len.hex()')
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g.code_start_pos = g.buf.len
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g.debug_pos = g.buf.len
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g.call(placeholder) // call main function, it's not guaranteed to be the first, we don't know its address yet
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g.println('call fn main')
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}
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pub fn (mut g Gen) generate_elf_footer() {
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// Return 0
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/*
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g.mov(.edi, 0) // ret value
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g.mov(.eax, 60)
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g.syscall()
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*/
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// Strings table
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// Loop thru all strings and set the right addresses
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for i, s in g.strings {
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g.write64_at(segment_start + g.buf.len, int(g.str_pos[i]))
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g.write_string(s)
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g.write8(0)
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}
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// Now we know the file size, set it
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file_size := g.buf.len
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g.write64_at(file_size, g.file_size_pos) // set file size 64 bit value
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g.write64_at(file_size, g.file_size_pos + 8)
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// call main function, it's not guaranteed to be the first
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// we generated call(0) ("e8 0")
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// now need to replace "0" with a relative address of the main function
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// +1 is for "e8"
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// -5 is for "e8 00 00 00 00"
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g.write32_at(g.code_start_pos + 1, int(g.main_fn_addr - g.code_start_pos) - 5)
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// Create the binary
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mut f := os.create(g.out_name) or {
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panic(err)
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}
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os.chmod(g.out_name, 0o775) // make it an executable
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f.write_bytes(g.buf.data, g.buf.len)
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f.close()
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println('\nx64 elf binary has been successfully generated')
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}
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