nac3/nac3ld/src/dwarf.rs

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Rust
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#![allow(non_camel_case_types, non_upper_case_globals)]
use std::mem;
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use byteorder::{ByteOrder, LittleEndian};
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pub const DW_EH_PE_omit: u8 = 0xFF;
pub const DW_EH_PE_absptr: u8 = 0x00;
pub const DW_EH_PE_uleb128: u8 = 0x01;
pub const DW_EH_PE_udata2: u8 = 0x02;
pub const DW_EH_PE_udata4: u8 = 0x03;
pub const DW_EH_PE_udata8: u8 = 0x04;
pub const DW_EH_PE_sleb128: u8 = 0x09;
pub const DW_EH_PE_sdata2: u8 = 0x0A;
pub const DW_EH_PE_sdata4: u8 = 0x0B;
pub const DW_EH_PE_sdata8: u8 = 0x0C;
pub const DW_EH_PE_pcrel: u8 = 0x10;
pub const DW_EH_PE_textrel: u8 = 0x20;
pub const DW_EH_PE_datarel: u8 = 0x30;
pub const DW_EH_PE_funcrel: u8 = 0x40;
pub const DW_EH_PE_aligned: u8 = 0x50;
pub const DW_EH_PE_indirect: u8 = 0x80;
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pub struct DwarfReader<'a> {
pub slice: &'a [u8],
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pub virt_addr: u32,
}
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impl<'a> DwarfReader<'a> {
pub fn new(slice: &[u8], virt_addr: u32) -> DwarfReader {
DwarfReader { slice, virt_addr }
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}
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pub fn offset(&mut self, offset: i32) {
self.slice = &self.slice[offset as usize..];
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self.virt_addr = self.virt_addr.wrapping_add(offset as u32);
}
// ULEB128 and SLEB128 encodings are defined in Section 7.6 - "Variable
// Length Data".
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pub fn read_uleb128(&mut self) -> u64 {
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let mut shift: usize = 0;
let mut result: u64 = 0;
let mut byte: u8;
loop {
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byte = self.read_u8();
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result |= ((byte & 0x7F) as u64) << shift;
shift += 7;
if byte & 0x80 == 0 {
break;
}
}
result
}
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pub fn read_sleb128(&mut self) -> i64 {
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let mut shift: u32 = 0;
let mut result: u64 = 0;
let mut byte: u8;
loop {
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byte = self.read_u8();
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result |= ((byte & 0x7F) as u64) << shift;
shift += 7;
if byte & 0x80 == 0 {
break;
}
}
// sign-extend
if shift < u64::BITS && (byte & 0x40) != 0 {
result |= (!0 as u64) << shift;
}
result as i64
}
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pub fn read_u8(&mut self) -> u8 {
let val = self.slice[0];
self.slice = &self.slice[1..];
val
}
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}
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macro_rules! impl_read_fn {
( $($type: ty, $byteorder_fn: ident);* ) => {
impl<'a> DwarfReader<'a> {
$(
pub fn $byteorder_fn(&mut self) -> $type {
let val = LittleEndian::$byteorder_fn(self.slice);
self.slice = &self.slice[mem::size_of::<$type>()..];
val
}
)*
}
}
}
impl_read_fn!(
u16, read_u16;
u32, read_u32;
u64, read_u64;
i16, read_i16;
i32, read_i32;
i64, read_i64
);
pub struct DwarfWriter<'a> {
pub slice: &'a mut [u8],
pub offset: usize,
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}
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impl<'a> DwarfWriter<'a> {
pub fn new(slice: &mut [u8]) -> DwarfWriter {
DwarfWriter { slice, offset: 0 }
}
pub fn write_u8(&mut self, data: u8) {
self.slice[self.offset] = data;
self.offset += 1;
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}
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pub fn write_u32(&mut self, data: u32) {
LittleEndian::write_u32(&mut self.slice[self.offset..], data);
self.offset += 4;
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}
}
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fn read_encoded_pointer(reader: &mut DwarfReader, encoding: u8) -> Result<usize, ()> {
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if encoding == DW_EH_PE_omit {
return Err(());
}
// DW_EH_PE_aligned implies it's an absolute pointer value
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// However, we are linking library for 32-bits architecture
// The size of variable should be 4 bytes instead
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if encoding == DW_EH_PE_aligned {
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let shifted_virt_addr = round_up(reader.virt_addr as usize, mem::size_of::<u32>())?;
let addr_inc = shifted_virt_addr - reader.virt_addr as usize;
reader.slice = &reader.slice[addr_inc..];
reader.virt_addr = shifted_virt_addr as u32;
return Ok(reader.read_u32() as usize);
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}
match encoding & 0x0F {
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DW_EH_PE_absptr => Ok(reader.read_u32() as usize),
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DW_EH_PE_uleb128 => Ok(reader.read_uleb128() as usize),
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DW_EH_PE_udata2 => Ok(reader.read_u16() as usize),
DW_EH_PE_udata4 => Ok(reader.read_u32() as usize),
DW_EH_PE_udata8 => Ok(reader.read_u64() as usize),
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DW_EH_PE_sleb128 => Ok(reader.read_sleb128() as usize),
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DW_EH_PE_sdata2 => Ok(reader.read_i16() as usize),
DW_EH_PE_sdata4 => Ok(reader.read_i32() as usize),
DW_EH_PE_sdata8 => Ok(reader.read_i64() as usize),
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_ => Err(()),
}
}
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fn read_encoded_pointer_with_pc(
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reader: &mut DwarfReader,
encoding: u8,
) -> Result<usize, ()> {
let entry_virt_addr = reader.virt_addr;
let mut result = read_encoded_pointer(reader, encoding)?;
// DW_EH_PE_aligned implies it's an absolute pointer value
if encoding == DW_EH_PE_aligned {
return Ok(result);
}
result = match encoding & 0x70 {
DW_EH_PE_pcrel => result.wrapping_add(entry_virt_addr as usize),
// .eh_frame normally would not have these kinds of relocations
// These would not be supported by a dedicated linker relocation schemes for RISC-V
DW_EH_PE_textrel | DW_EH_PE_datarel | DW_EH_PE_funcrel | DW_EH_PE_aligned => {
unimplemented!()
}
// Other values should be impossible
_ => unreachable!(),
};
if encoding & DW_EH_PE_indirect != 0 {
// There should not be a need for indirect addressing, as assembly code from
// the dynamic library should not be freely moved relative to the EH frame.
unreachable!()
}
Ok(result)
}
#[inline]
fn round_up(unrounded: usize, align: usize) -> Result<usize, ()> {
if align.is_power_of_two() {
Ok((unrounded + align - 1) & !(align - 1))
} else {
Err(())
}
}
// Minimalistic structure to store everything needed for parsing FDEs to synthesize
// .eh_frame_hdr section. Since we are only linking 1 object file, there should only be 1 call
// frame information (CFI) record, so there should be only 1 common information entry (CIE).
// So the class parses the only CIE on init, cache the encoding info, then parse the FDE on
// iterations based on the cached encoding format.
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pub struct EH_Frame<'a> {
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// It refers to the augmentation data that corresponds to 'R' in the augmentation string
pub fde_pointer_encoding: u8,
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pub fde_reader: DwarfReader<'a>,
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pub fde_sz: usize,
}
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impl<'a> EH_Frame<'a> {
pub fn new(eh_frame_slice: &[u8], eh_frame_addr: u32) -> Result<EH_Frame, ()> {
let mut cie_reader = DwarfReader::new(eh_frame_slice, eh_frame_addr);
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let eh_frame_size = eh_frame_slice.len();
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let length = cie_reader.read_u32();
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let fde_reader = match length {
// eh_frame with 0 lengths means the CIE is terminated
// while length == u32::MAX means that the length is only representable with 64 bits,
// which does not make sense in a system with 32-bit address.
0 | 0xFFFFFFFF => unimplemented!(),
_ => {
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let mut fde_reader = DwarfReader::new(cie_reader.slice, cie_reader.virt_addr);
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fde_reader.offset(length as i32);
fde_reader
}
};
let fde_sz = eh_frame_size - mem::size_of::<u32>() - length as usize;
// Routine check on the .eh_frame well-formness, in terms of CIE ID & Version args.
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assert_eq!(cie_reader.read_u32(), 0);
assert_eq!(cie_reader.read_u8(), 1);
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// Parse augmentation string
// The first character must be 'z', there is no way to proceed otherwise
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assert_eq!(cie_reader.read_u8(), b'z');
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// Establish a pointer that skips ahead of the string
// Skip code/data alignment factors & return address register along the way as well
// We only tackle the case where 'z' and 'R' are part of the augmentation string, otherwise
// we cannot get the addresses to make .eh_frame_hdr
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let mut aug_data_reader = DwarfReader::new(cie_reader.slice, cie_reader.virt_addr);
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let mut aug_str_len = 0;
loop {
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if aug_data_reader.read_u8() == b'\0' {
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break;
}
aug_str_len += 1;
}
if aug_str_len == 0 {
unimplemented!();
}
aug_data_reader.read_uleb128(); // Code alignment factor
aug_data_reader.read_sleb128(); // Data alignment factor
aug_data_reader.read_uleb128(); // Return address register
aug_data_reader.read_uleb128(); // Augmentation data length
let mut fde_pointer_encoding = DW_EH_PE_omit;
for _ in 0..aug_str_len {
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match cie_reader.read_u8() {
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b'L' => {
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aug_data_reader.read_u8();
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}
b'P' => {
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let encoding = aug_data_reader.read_u8();
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read_encoded_pointer(&mut aug_data_reader, encoding)?;
}
b'R' => {
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fde_pointer_encoding = aug_data_reader.read_u8();
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}
// Other characters are not supported
_ => unimplemented!(),
}
}
assert_ne!(fde_pointer_encoding, DW_EH_PE_omit);
Ok(EH_Frame { fde_pointer_encoding, fde_reader, fde_sz })
}
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pub fn iterate_fde(&self, callback: &mut dyn FnMut(u32, u32)) -> Result<(), ()> {
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// Parse each FDE to obtain the starting address that the FDE applies to
// Send the FDE offset and the mentioned address to a callback that write up the
// .eh_frame_hdr section
let mut remaining_len = self.fde_sz;
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let mut reader = DwarfReader::new(self.fde_reader.slice, self.fde_reader.virt_addr);
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loop {
if remaining_len == 0 {
break;
}
let fde_virt_addr = reader.virt_addr;
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let length = match reader.read_u32() {
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0 | 0xFFFFFFFF => unimplemented!(),
other => other,
};
// Remove the length of the header and the content from the counter
remaining_len -= length as usize + mem::size_of::<u32>();
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let mut next_fde_reader = DwarfReader::new(reader.slice, reader.virt_addr);
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next_fde_reader.offset(length as i32);
// Skip CIE pointer offset
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reader.read_u32();
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// Parse PC Begin using the encoding scheme mentioned in the CIE
let pc_begin = read_encoded_pointer_with_pc(&mut reader, self.fde_pointer_encoding)?;
callback(pc_begin as u32, fde_virt_addr);
reader = next_fde_reader;
}
Ok(())
}
}
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pub struct EH_Frame_Hdr<'a> {
fde_writer: DwarfWriter<'a>,
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eh_frame_hdr_addr: u32,
fdes: Vec<(u32, u32)>,
}
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impl<'a> EH_Frame_Hdr<'a> {
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// Create a EH_Frame_Hdr object, and write out the fixed fields of .eh_frame_hdr to memory
// eh_frame_ptr_enc will be 0x1B (PC-relative, 4 bytes)
// table_enc will be 0x3B (Relative to the start of .eh_frame_hdr, 4 bytes)
// Load address is not known at this point.
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pub fn new(
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eh_frame_hdr_slice: &mut [u8],
eh_frame_hdr_addr: u32,
eh_frame_addr: u32,
) -> EH_Frame_Hdr {
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let mut writer = DwarfWriter::new(eh_frame_hdr_slice);
writer.write_u8(1);
writer.write_u8(0x1B);
writer.write_u8(0x03);
writer.write_u8(0x3B);
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let eh_frame_offset =
(eh_frame_addr).wrapping_sub(eh_frame_hdr_addr + ((mem::size_of::<u8>() as u32) * 4));
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writer.write_u32(eh_frame_offset);
writer.write_u32(0);
EH_Frame_Hdr { fde_writer: writer, eh_frame_hdr_addr, fdes: Vec::new() }
}
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fn fde_count_offset() -> usize {
8
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}
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pub fn add_fde(&mut self, init_loc: u32, addr: u32) {
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self.fdes.push((
init_loc.wrapping_sub(self.eh_frame_hdr_addr),
addr.wrapping_sub(self.eh_frame_hdr_addr),
));
}
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pub fn finalize_fde(mut self) {
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self.fdes
.sort_by(|(left_init_loc, _), (right_init_loc, _)| left_init_loc.cmp(right_init_loc));
for (init_loc, addr) in &self.fdes {
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self.fde_writer.write_u32(*init_loc);
self.fde_writer.write_u32(*addr);
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}
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LittleEndian::write_u32(&mut self.fde_writer.slice[Self::fde_count_offset()..], self.fdes.len() as u32);
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}
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pub fn size_from_eh_frame(eh_frame: &[u8]) -> usize {
// The virtual address of the EH frame does not matter in this case
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// Calculation of size does not involve modifying any headers
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let mut reader = DwarfReader::new(eh_frame, 0);
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let mut fde_count = 0;
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while !reader.slice.is_empty() {
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// The original length field should be able to hold the entire value.
// The device memory space is limited to 32-bits addresses anyway.
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let entry_length = reader.read_u32();
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if entry_length == 0 || entry_length == 0xFFFFFFFF {
unimplemented!()
}
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if reader.read_u32() != 0 {
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fde_count += 1;
}
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reader.offset(entry_length as i32 - mem::size_of::<u32>() as i32)
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}
12 + fde_count * 8
}
}