//! Helper for writing COFF files.
use alloc::string::String;
use alloc::vec::Vec;
use core::mem;
use crate::endian::{LittleEndian as LE, U16Bytes, U32Bytes, U16, U32};
use crate::pe;
use crate::write::string::{StringId, StringTable};
use crate::write::util;
use crate::write::{Error, Result, WritableBuffer};
/// A helper for writing COFF files.
///
/// Writing uses a two phase approach. The first phase builds up all of the information
/// that may need to be known ahead of time:
/// - build string table
/// - reserve section indices
/// - reserve symbol indices
/// - reserve file ranges for headers and sections
///
/// Some of the information has ordering requirements. For example, strings must be added
/// to the string table before reserving the file range for the string table. There are debug
/// asserts to check some of these requirements.
///
/// The second phase writes everything out in order. Thus the caller must ensure writing
/// is in the same order that file ranges were reserved. There are debug asserts to assist
/// with checking this.
#[allow(missing_debug_implementations)]
pub struct Writer<'a> {
buffer: &'a mut dyn WritableBuffer,
len: usize,
section_num: u16,
symtab_offset: u32,
symtab_num: u32,
strtab: StringTable<'a>,
strtab_len: usize,
strtab_offset: u32,
strtab_data: Vec<u8>,
}
impl<'a> Writer<'a> {
/// Create a new `Writer`.
pub fn new(buffer: &'a mut dyn WritableBuffer) -> Self {
Writer {
buffer,
len: 0,
section_num: 0,
symtab_offset: 0,
symtab_num: 0,
strtab: StringTable::default(),
strtab_len: 0,
strtab_offset: 0,
strtab_data: Vec::new(),
}
}
/// Return the current file length that has been reserved.
pub fn reserved_len(&self) -> usize {
self.len
}
/// Return the current file length that has been written.
#[allow(clippy::len_without_is_empty)]
pub fn len(&self) -> usize {
self.buffer.len()
}
/// Reserve a file range with the given size and starting alignment.
///
/// Returns the aligned offset of the start of the range.
///
/// `align_start` must be a power of two.
pub fn reserve(&mut self, len: usize, align_start: usize) -> u32 {
if align_start > 1 {
self.len = util::align(self.len, align_start);
}
let offset = self.len;
self.len += len;
offset as u32
}
/// Write alignment padding bytes.
pub fn write_align(&mut self, align_start: usize) {
if align_start > 1 {
util::write_align(self.buffer, align_start);
}
}
/// Write data.
pub fn write(&mut self, data: &[u8]) {
self.buffer.write_bytes(data);
}
/// Reserve the file range up to the given file offset.
pub fn reserve_until(&mut self, offset: usize) {
debug_assert!(self.len <= offset);
self.len = offset;
}
/// Write padding up to the given file offset.
pub fn pad_until(&mut self, offset: usize) {
debug_assert!(self.buffer.len() <= offset);
self.buffer.resize(offset);
}
/// Reserve the range for the file header.
///
/// This must be at the start of the file.
pub fn reserve_file_header(&mut self) {
debug_assert_eq!(self.len, 0);
self.reserve(mem::size_of::<pe::ImageFileHeader>(), 1);
}
/// Write the file header.
///
/// This must be at the start of the file.
///
/// Fields that can be derived from known information are automatically set by this function.
pub fn write_file_header(&mut self, header: FileHeader) -> Result<()> {
debug_assert_eq!(self.buffer.len(), 0);
// Start writing.
self.buffer
.reserve(self.len)
.map_err(|_| Error(String::from("Cannot allocate buffer")))?;
// Write file header.
let header = pe::ImageFileHeader {
machine: U16::new(LE, header.machine),
number_of_sections: U16::new(LE, self.section_num),
time_date_stamp: U32::new(LE, header.time_date_stamp),
pointer_to_symbol_table: U32::new(LE, self.symtab_offset),
number_of_symbols: U32::new(LE, self.symtab_num),
size_of_optional_header: U16::default(),
characteristics: U16::new(LE, header.characteristics),
};
self.buffer.write(&header);
Ok(())
}
/// Reserve the range for the section headers.
pub fn reserve_section_headers(&mut self, section_num: u16) {
debug_assert_eq!(self.section_num, 0);
self.section_num = section_num;
self.reserve(
section_num as usize * mem::size_of::<pe::ImageSectionHeader>(),
1,
);
}
/// Write a section header.
pub fn write_section_header(&mut self, section: SectionHeader) {
let mut coff_section = pe::ImageSectionHeader {
name: [0; 8],
virtual_size: U32::default(),
virtual_address: U32::default(),
size_of_raw_data: U32::new(LE, section.size_of_raw_data),
pointer_to_raw_data: U32::new(LE, section.pointer_to_raw_data),
pointer_to_relocations: U32::new(LE, section.pointer_to_relocations),
pointer_to_linenumbers: U32::new(LE, section.pointer_to_linenumbers),
number_of_relocations: if section.number_of_relocations > 0xffff {
U16::new(LE, 0xffff)
} else {
U16::new(LE, section.number_of_relocations as u16)
},
number_of_linenumbers: U16::default(),
characteristics: U32::new(LE, section.characteristics),
};
match section.name {
Name::Short(name) => coff_section.name = name,
Name::Long(str_id) => {
let mut str_offset = self.strtab.get_offset(str_id);
if str_offset <= 9_999_999 {
let mut name = [0; 7];
let mut len = 0;
if str_offset == 0 {
name[6] = b'0';
len = 1;
} else {
while str_offset != 0 {
let rem = (str_offset % 10) as u8;
str_offset /= 10;
name[6 - len] = b'0' + rem;
len += 1;
}
}
coff_section.name = [0; 8];
coff_section.name[0] = b'/';
coff_section.name[1..][..len].copy_from_slice(&name[7 - len..]);
} else {
debug_assert!(str_offset as u64 <= 0xf_ffff_ffff);
coff_section.name[0] = b'/';
coff_section.name[1] = b'/';
for i in 0..6 {
let rem = (str_offset % 64) as u8;
str_offset /= 64;
let c = match rem {
0..=25 => b'A' + rem,
26..=51 => b'a' + rem - 26,
52..=61 => b'0' + rem - 52,
62 => b'+',
63 => b'/',
_ => unreachable!(),
};
coff_section.name[7 - i] = c;
}
}
}
}
self.buffer.write(&coff_section);
}
/// Reserve the range for the section data.
///
/// Returns the aligned offset of the start of the range.
/// Does nothing and returns 0 if the length is zero.
pub fn reserve_section(&mut self, len: usize) -> u32 {
if len == 0 {
return 0;
}
// TODO: not sure what alignment is required here, but this seems to match LLVM
self.reserve(len, 4)
}
/// Write the alignment bytes prior to section data.
///
/// This is unneeded if you are using `write_section` or `write_section_zeroes`
/// for the data.
pub fn write_section_align(&mut self) {
util::write_align(self.buffer, 4);
}
/// Write the section data.
///
/// Writes alignment bytes prior to the data.
/// Does nothing if the data is empty.
pub fn write_section(&mut self, data: &[u8]) {
if data.is_empty() {
return;
}
self.write_section_align();
self.buffer.write_bytes(data);
}
/// Write the section data using zero bytes.
///
/// Writes alignment bytes prior to the data.
/// Does nothing if the length is zero.
pub fn write_section_zeroes(&mut self, len: usize) {
if len == 0 {
return;
}
self.write_section_align();
self.buffer.resize(self.buffer.len() + len);
}
/// Reserve a file range for the given number of relocations.
///
/// This will automatically reserve an extra relocation if there are more than 0xffff.
///
/// Returns the offset of the range.
/// Does nothing and returns 0 if the count is zero.
pub fn reserve_relocations(&mut self, mut count: usize) -> u32 {
if count == 0 {
return 0;
}
if count > 0xffff {
count += 1;
}
self.reserve(count * mem::size_of::<pe::ImageRelocation>(), 1)
}
/// Write a relocation containing the count if required.
///
/// This should be called before writing the first relocation for a section.
pub fn write_relocations_count(&mut self, count: usize) {
if count > 0xffff {
let coff_relocation = pe::ImageRelocation {
virtual_address: U32Bytes::new(LE, count as u32 + 1),
symbol_table_index: U32Bytes::new(LE, 0),
typ: U16Bytes::new(LE, 0),
};
self.buffer.write(&coff_relocation);
}
}
/// Write a relocation.
pub fn write_relocation(&mut self, reloc: Relocation) {
let coff_relocation = pe::ImageRelocation {
virtual_address: U32Bytes::new(LE, reloc.virtual_address),
symbol_table_index: U32Bytes::new(LE, reloc.symbol),
typ: U16Bytes::new(LE, reloc.typ),
};
self.buffer.write(&coff_relocation);
}
/// Reserve a symbol table entry.
///
/// This must be called before [`Self::reserve_symtab_strtab`].
pub fn reserve_symbol_index(&mut self) -> u32 {
debug_assert_eq!(self.symtab_offset, 0);
let index = self.symtab_num;
self.symtab_num += 1;
index
}
/// Reserve a number of symbol table entries.
pub fn reserve_symbol_indices(&mut self, count: u32) {
debug_assert_eq!(self.symtab_offset, 0);
self.symtab_num += count;
}
/// Write a symbol table entry.
pub fn write_symbol(&mut self, symbol: Symbol) {
let mut coff_symbol = pe::ImageSymbol {
name: [0; 8],
value: U32Bytes::new(LE, symbol.value),
section_number: U16Bytes::new(LE, symbol.section_number),
typ: U16Bytes::new(LE, symbol.typ),
storage_class: symbol.storage_class,
number_of_aux_symbols: symbol.number_of_aux_symbols,
};
match symbol.name {
Name::Short(name) => coff_symbol.name = name,
Name::Long(str_id) => {
let str_offset = self.strtab.get_offset(str_id);
coff_symbol.name[4..8].copy_from_slice(&u32::to_le_bytes(str_offset as u32));
}
}
self.buffer.write(&coff_symbol);
}
/// Reserve auxiliary symbols for a file name.
///
/// Returns the number of auxiliary symbols required.
///
/// This must be called before [`Self::reserve_symtab_strtab`].
pub fn reserve_aux_file_name(&mut self, name: &[u8]) -> u8 {
debug_assert_eq!(self.symtab_offset, 0);
let aux_count = (name.len() + pe::IMAGE_SIZEOF_SYMBOL - 1) / pe::IMAGE_SIZEOF_SYMBOL;
self.symtab_num += aux_count as u32;
aux_count as u8
}
/// Write auxiliary symbols for a file name.
pub fn write_aux_file_name(&mut self, name: &[u8], aux_count: u8) {
let aux_len = aux_count as usize * pe::IMAGE_SIZEOF_SYMBOL;
debug_assert!(aux_len >= name.len());
let old_len = self.buffer.len();
self.buffer.write_bytes(name);
self.buffer.resize(old_len + aux_len);
}
/// Reserve an auxiliary symbol for a section.
///
/// Returns the number of auxiliary symbols required.
///
/// This must be called before [`Self::reserve_symtab_strtab`].
pub fn reserve_aux_section(&mut self) -> u8 {
debug_assert_eq!(self.symtab_offset, 0);
self.symtab_num += 1;
1
}
/// Write an auxiliary symbol for a section.
pub fn write_aux_section(&mut self, section: AuxSymbolSection) {
let aux = pe::ImageAuxSymbolSection {
length: U32Bytes::new(LE, section.length),
number_of_relocations: if section.number_of_relocations > 0xffff {
U16Bytes::new(LE, 0xffff)
} else {
U16Bytes::new(LE, section.number_of_relocations as u16)
},
number_of_linenumbers: U16Bytes::new(LE, section.number_of_linenumbers),
check_sum: U32Bytes::new(LE, section.check_sum),
number: U16Bytes::new(LE, section.number as u16),
selection: section.selection,
reserved: 0,
high_number: U16Bytes::new(LE, (section.number >> 16) as u16),
};
self.buffer.write(&aux);
}
/// Return the number of reserved symbol table entries.
pub fn symbol_count(&self) -> u32 {
self.symtab_num
}
/// Add a string to the string table.
///
/// This must be called before [`Self::reserve_symtab_strtab`].
pub fn add_string(&mut self, name: &'a [u8]) -> StringId {
debug_assert_eq!(self.strtab_offset, 0);
self.strtab.add(name)
}
/// Add a section or symbol name to the string table if required.
///
/// This must be called before [`Self::reserve_symtab_strtab`].
pub fn add_name(&mut self, name: &'a [u8]) -> Name {
if name.len() > 8 {
Name::Long(self.add_string(name))
} else {
let mut short_name = [0; 8];
short_name[..name.len()].copy_from_slice(name);
Name::Short(short_name)
}
}
/// Reserve the range for the symbol table and string table.
///
/// This must be called after functions that reserve symbol
/// indices or add strings.
pub fn reserve_symtab_strtab(&mut self) {
debug_assert_eq!(self.symtab_offset, 0);
self.symtab_offset = self.reserve(self.symtab_num as usize * pe::IMAGE_SIZEOF_SYMBOL, 1
);
debug_assert_eq!(self.strtab_offset, 0);
// First 4 bytes of strtab are the length.
self.strtab.write(4, &mut self.strtab_data);
self.strtab_len = self.strtab_data.len() + 4;
self.strtab_offset = self.reserve(self.strtab_len, 1);
}
/// Write the string table.
pub fn write_strtab(&mut self) {
debug_assert_eq!(self.strtab_offset, self.buffer.len() as u32);
self.buffer
.write_bytes(&u32::to_le_bytes(self.strtab_len as u32));
self.buffer.write_bytes(&self.strtab_data);
}
}
/// Shortened and native endian version of [`pe::ImageFileHeader`].
#[allow(missing_docs)]
#[derive(Debug, Default, Clone)]
pub struct FileHeader {
pub machine: u16,
pub time_date_stamp: u32,
pub characteristics: u16,
}
/// A section or symbol name.
#[derive(Debug, Clone, Copy)]
pub enum Name {
/// An inline name.
Short([u8; 8]),
/// An id of a string table entry.
Long(StringId),
}
impl Default for Name {
fn default() -> Name {
Name::Short([0; 8])
}
}
// From isn't useful.
#[allow(clippy::from_over_into)]
impl<'a> Into<Name> for &'a [u8; 8] {
fn into(self) -> Name {
Name::Short(*self)
}
}
/// Native endian version of [`pe::ImageSectionHeader`].
#[allow(missing_docs)]
#[derive(Debug, Default, Clone)]
pub struct SectionHeader {
pub name: Name,
pub size_of_raw_data: u32,
pub pointer_to_raw_data: u32,
pub pointer_to_relocations: u32,
pub pointer_to_linenumbers: u32,
/// This will automatically be clamped if there are more than 0xffff.
pub number_of_relocations: u32,
pub number_of_linenumbers: u16,
pub characteristics: u32,
}
/// Native endian version of [`pe::ImageSymbol`].
#[allow(missing_docs)]
#[derive(Debug, Default, Clone)]
pub struct Symbol {
pub name: Name,
pub value: u32,
pub section_number: u16,
pub typ: u16,
pub storage_class: u8,
pub number_of_aux_symbols: u8,
}
/// Native endian version of [`pe::ImageAuxSymbolSection`].
#[allow(missing_docs)]
#[derive(Debug, Default, Clone)]
pub struct AuxSymbolSection {
pub length: u32,
/// This will automatically be clamped if there are more than 0xffff.
pub number_of_relocations: u32,
pub number_of_linenumbers: u16,
pub check_sum: u32,
pub number: u32,
pub selection: u8,
}
/// Native endian version of [`pe::ImageRelocation`].
#[allow(missing_docs)]
#[derive(Debug, Default, Clone)]
pub struct Relocation {
pub virtual_address: u32,
pub symbol: u32,
pub typ: u16,
}
