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// Copyright (c) 2019-2021 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module native
const (
mag0 = byte(0x7f)
mag1 = `E`
mag2 = `L`
mag3 = `F`
ei_class = 4
elfclass64 = 2
elfdata2lsb = 1
ev_current = 1
)
// ELF file types
const (
elf_osabi = 0
et_rel = 1
et_exec = 2
et_dyn = 3
e_machine_amd64 = 0x3e
e_machine_arm64 = 0xb7
shn_xindex = 0xffff
sht_null = 0
)
const (
segment_start = 0x400000
placeholder = 0
sevens = 0x77777777
)
pub fn (mut g Gen) generate_elf_header() {
g.buf << [byte(native.mag0), native.mag1, native.mag2, native.mag3]
g.buf << native.elfclass64 // file class
g.buf << native.elfdata2lsb // data encoding
g.buf << native.ev_current // file version
g.buf << native.elf_osabi
g.write64(0) // et_rel) // et_rel for .o
g.write16(2) // e_type
if g.pref.arch == .arm64 {
g.write16(native.e_machine_arm64)
} else {
g.write16(native.e_machine_amd64)
}
g.write32(native.ev_current) // e_version
eh_size := 0x40
phent_size := 0x38
g.write64(native.segment_start + eh_size + phent_size) // e_entry
g.write64(0x40) // e_phoff
g.write64(0) // e_shoff
g.write32(0) // e_flags
g.write16(eh_size) // e_ehsize
g.write16(phent_size) // e_phentsize
g.write16(1) // e_phnum
g.write16(0) // e_shentsize
g.write16(0) // e_shnum (number of sections)
g.write16(0) // e_shstrndx
// Elf64_Phdr
g.write32(1) // p_type
g.write32(5) // p_flags
g.write64(0) // p_offset
g.write64(native.segment_start) // p_vaddr addr:050
g.write64(native.segment_start) //
g.file_size_pos = i64(g.buf.len)
g.write64(0) // p_filesz PLACEHOLDER, set to file_size later // addr: 060
g.write64(0) // p_memsz
g.write64(0x1000) // p_align
// user code starts here at
// address: 00070 and a half
if g.pref.is_verbose {
eprintln('code_start_pos = $g.buf.len.hex()')
}
g.code_start_pos = i64(g.buf.len)
g.debug_pos = g.buf.len
g.call(native.placeholder) // call main function, it's not guaranteed to be the first, we don't know its address yet
g.println('; call fn main')
}
pub fn (mut g Gen) generate_elf_footer() {
// Return 0
/*
g.mov(.edi, 0) // ret value
g.mov(.eax, 60)
g.syscall()
*/
// Strings table
// Loop thru all strings and set the right addresses
for i, s in g.strings {
g.write64_at(native.segment_start + g.buf.len, int(g.str_pos[i]))
g.write_string(s)
g.write8(0)
}
// Now we know the file size, set it
file_size := g.buf.len
g.write64_at(file_size, g.file_size_pos) // set file size 64 bit value
g.write64_at(file_size, g.file_size_pos + 8)
if g.pref.arch == .arm64 {
bl_next := u32(0x94000001)
g.write32_at(g.code_start_pos, int(bl_next))
} else {
// amd64
// call main function, it's not guaranteed to be the first
// we generated call(0) ("e8 0")
// now need to replace "0" with a relative address of the main function
// +1 is for "e8"
// -5 is for "e8 00 00 00 00"
g.write32_at(g.code_start_pos + 1, int(g.main_fn_addr - g.code_start_pos) - 5)
}
g.create_executable()
}
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