//! # Relocation computations
//!
//! The following notation is used to describe relocation computations
//! specific to x86_64 ELF.
//!
//! * A: The addend used to compute the value of the relocatable field.
//! * B: The base address at which a shared object is loaded into memory
//! during execution. Generally, a shared object file is built with a
//! base virtual address of 0. However, the execution address of the
//! shared object is different.
//! * G: The offset into the global offset table at which the address of
//! the relocation entry's symbol resides during execution.
//! * GOT: The address of the global offset table.
//! * L: The section offset or address of the procedure linkage table entry
//! for a symbol.
//! * P: The section offset or address of the storage unit being relocated,
//! computed using r_offset.
//! * S: The value of the symbol whose index resides in the relocation entry.
//! * Z: The size of the symbol whose index resides in the relocation entry.
//!
//! Below are some common x86_64 relocation computations you might find useful:
//!
//! | Relocation | Value | Size | Formula |
//! |:--------------------------|:------|:----------|:------------------|
//! | `R_X86_64_NONE` | 0 | NONE | NONE |
//! | `R_X86_64_64` | 1 | 64 | S + A |
//! | `R_X86_64_PC32` | 2 | 32 | S + A - P |
//! | `R_X86_64_GOT32` | 3 | 32 | G + A |
//! | `R_X86_64_PLT32` | 4 | 32 | L + A - P |
//! | `R_X86_64_COPY` | 5 | NONE | NONE |
//! | `R_X86_64_GLOB_DAT` | 6 | 64 | S |
//! | `R_X86_64_JUMP_SLOT` | 7 | 64 | S |
//! | `R_X86_64_RELATIVE` | 8 | 64 | B + A |
//! | `R_X86_64_GOTPCREL` | 9 | 32 | G + GOT + A - P |
//! | `R_X86_64_32` | 10 | 32 | S + A |
//! | `R_X86_64_32S` | 11 | 32 | S + A |
//! | `R_X86_64_16` | 12 | 16 | S + A |
//! | `R_X86_64_PC16` | 13 | 16 | S + A - P |
//! | `R_X86_64_8` | 14 | 8 | S + A |
//! | `R_X86_64_PC8` | 15 | 8 | S + A - P |
//! | `R_X86_64_DTPMOD64` | 16 | 64 | |
//! | `R_X86_64_DTPOFF64` | 17 | 64 | |
//! | `R_X86_64_TPOFF64` | 18 | 64 | |
//! | `R_X86_64_TLSGD` | 19 | 32 | |
//! | `R_X86_64_TLSLD` | 20 | 32 | |
//! | `R_X86_64_DTPOFF32` | 21 | 32 | |
//! | `R_X86_64_GOTTPOFF` | 22 | 32 | |
//! | `R_X86_64_TPOFF32` | 23 | 32 | |
//! | `R_X86_64_PC64` | 24 | 64 | S + A - P |
//! | `R_X86_64_GOTOFF64` | 25 | 64 | S + A - GOT |
//! | `R_X86_64_GOTPC32` | 26 | 32 | GOT + A - P |
//! | `R_X86_64_SIZE32` | 32 | 32 | Z + A |
//! | `R_X86_64_SIZE64` | 33 | 64 | Z + A |
//! | `R_X86_64_GOTPC32_TLSDESC`| 34 | 32 | |
//! | `R_X86_64_TLSDESC_CALL` | 35 | NONE | |
//! | `R_X86_64_TLSDESC` | 36 | 64 × 2 | |
//! | `R_X86_64_IRELATIVE` | 37 | 64 | indirect (B + A) |
//!
//! TLS information is at <
http://people.redhat.com/aoliva/writeups/TLS/RFC-TLSDESC-x86.txt>
//!
//! `R_X86_64_IRELATIVE` is similar to `R_X86_64_RELATIVE` except that
//! the value used in this relocation is the program address returned by the function,
//! which takes no arguments, at the address of the result of the corresponding
//! `R_X86_64_RELATIVE` relocation.
//!
//! Read more <
https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-54839.html>
include!("constants_relocation.rs");
macro_rules! elf_reloc {
($size:ident, $isize:ty) => {
use core::fmt;
#[cfg(feature = "alloc")]
use scroll::{Pread, Pwrite, SizeWith};
#[repr(C)]
#[derive(Clone, Copy, PartialEq, Default)]
#[cfg_attr(feature = "alloc", derive(Pread, Pwrite, SizeWith))]
/// Relocation with an explicit addend
pub struct Rela {
/// Address
pub r_offset: $size,
/// Relocation type and symbol index
pub r_info: $size,
/// Addend
pub r_addend: $isize,
}
#[repr(C)]
#[derive(Clone, PartialEq, Default)]
#[cfg_attr(feature = "alloc", derive(Pread, Pwrite, SizeWith))]
/// Relocation without an addend
pub struct Rel {
/// address
pub r_offset: $size,
/// relocation type and symbol address
pub r_info: $size,
}
use plain;
unsafe impl plain::Plain for Rela {}
unsafe impl plain::Plain for Rel {}
impl fmt::Debug for Rela {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let sym = r_sym(self.r_info);
let typ = r_type(self.r_info);
f.debug_struct("Rela")
.field("r_offset", &format_args!("{:x}", self.r_offset))
.field("r_info", &format_args!("{:x}", self.r_info))
.field("r_addend", &format_args!("{:x}", self.r_addend))
.field("r_typ", &typ)
.field("r_sym", &sym)
.finish()
}
}
impl fmt::Debug for Rel {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let sym = r_sym(self.r_info);
let typ = r_type(self.r_info);
f.debug_struct("Rel")
.field("r_offset", &format_args!("{:x}", self.r_offset))
.field("r_info", &format_args!("{:x}", self.r_info))
.field("r_typ", &typ)
.field("r_sym", &sym)
.finish()
}
}
};
}
macro_rules! elf_rela_std_impl {
($size:ident, $isize:ty) => {
if_alloc! {
use core::slice;
if_std! {
use crate::error::Result;
use std::fs::File;
use std::io::{Read, Seek};
use std::io::SeekFrom::Start;
}
impl From<Rela> for Reloc {
fn from(rela: Rela) -> Self {
Reloc {
r_offset: u64::from(rela.r_offset),
r_addend: Some(i64::from(rela.r_addend)),
r_sym: r_sym(rela.r_info) as usize,
r_type: r_type(rela.r_info),
}
}
}
impl From<Rel> for Reloc {
fn from(rel: Rel) -> Self {
Reloc {
r_offset: u64::from(rel.r_offset),
r_addend: None,
r_sym: r_sym(rel.r_info) as usize,
r_type: r_type(rel.r_info),
}
}
}
impl From<Reloc> for Rela {
fn from(rela: Reloc) -> Self {
let r_info = r_info(rela.r_sym as $size, $size::from(rela.r_type));
Rela {
r_offset: rela.r_offset as $size,
r_info: r_info,
r_addend: rela.r_addend.unwrap_or(0) as $isize,
}
}
}
impl From<Reloc> for Rel {
fn from(rel: Reloc) -> Self {
let r_info = r_info(rel.r_sym as $size, $size::from(rel.r_type));
Rel {
r_offset: rel.r_offset as $size,
r_info: r_info,
}
}
}
/// Gets the rela entries given a rela pointer and the _size_ of the rela section in the binary,
/// in bytes.
/// Assumes the pointer is valid and can safely return a slice of memory pointing to the relas bec
ause:
/// 1. `ptr` points to memory received from the kernel (i.e., it loaded the executable), _or_
/// 2. The binary has already been mmapped (i.e., it's a `SharedObject`), and hence it's safe to return a slice of that memory.
/// 3. Or if you obtained the pointer in some other lawful manner
pub unsafe fn from_raw_rela<'a>(ptr: *const Rela, size: usize) -> &'a [Rela] {
slice::from_raw_parts(ptr, size / SIZEOF_RELA)
}
/// Gets the rel entries given a rel pointer and the _size_ of the rel section in the binary,
/// in bytes.
/// Assumes the pointer is valid and can safely return a slice of memory pointing to the rels because:
/// 1. `ptr` points to memory received from the kernel (i.e., it loaded the executable), _or_
/// 2. The binary has already been mmapped (i.e., it's a `SharedObject`), and hence it's safe to return a slice of that memory.
/// 3. Or if you obtained the pointer in some other lawful manner
pub unsafe fn from_raw_rel<'a>(ptr: *const Rel, size: usize) -> &'a [Rel] {
slice::from_raw_parts(ptr, size / SIZEOF_REL)
}
#[cfg(feature = "std")]
pub fn from_fd(fd: &mut File, offset: usize, size: usize) -> Result<Vec<Rela>> {
let count = size / SIZEOF_RELA;
let mut relocs = vec![Rela::default(); count];
fd.seek(Start(offset as u64))?;
unsafe {
fd.read_exact(plain::as_mut_bytes(&mut *relocs))?;
}
Ok(relocs)
}
} // end if_alloc
};
}
pub mod reloc32 {
pub use crate::elf::reloc::*;
elf_reloc!(u32, i32);
pub const SIZEOF_RELA: usize = 4 + 4 + 4;
pub const SIZEOF_REL: usize = 4 + 4;
#[inline(always)]
pub fn r_sym(info: u32) -> u32 {
info >> 8
}
#[inline(always)]
pub fn r_type(info: u32) -> u32 {
info & 0xff
}
#[inline(always)]
pub fn r_info(sym: u32, typ: u32) -> u32 {
(sym << 8) + (typ & 0xff)
}
elf_rela_std_impl!(u32, i32);
}
pub mod reloc64 {
pub use crate::elf::reloc::*;
elf_reloc!(u64, i64);
pub const SIZEOF_RELA: usize = 8 + 8 + 8;
pub const SIZEOF_REL: usize = 8 + 8;
#[inline(always)]
pub fn r_sym(info: u64) -> u32 {
(info >> 32) as u32
}
#[inline(always)]
pub fn r_type(info: u64) -> u32 {
(info & 0xffff_ffff) as u32
}
#[inline(always)]
pub fn r_info(sym: u64, typ: u64) -> u64 {
(sym << 32) + typ
}
elf_rela_std_impl!(u64, i64);
}
//////////////////////////////
// Generic Reloc
/////////////////////////////
if_alloc! {
use scroll::{ctx, Pread};
use scroll::ctx::SizeWith;
use core::fmt;
use core::result;
use crate::container::{Ctx, Container};
use alloc::vec::Vec;
#[derive(Clone, Copy, PartialEq, Default)]
/// A unified ELF relocation structure
pub struct Reloc {
/// Address
pub r_offset: u64,
/// Addend
pub r_addend: Option<i64>,
/// The index into the corresponding symbol table - either dynamic or regular
pub r_sym: usize,
/// The relocation type
pub r_type: u32,
}
impl Reloc {
pub fn size(is_rela: bool, ctx: Ctx) -> usize {
use scroll::ctx::SizeWith;
Reloc::size_with(&(is_rela, ctx))
}
}
type RelocCtx = (bool, Ctx);
impl ctx::SizeWith<RelocCtx> for Reloc {
fn size_with( &(is_rela, Ctx { container, .. }): &RelocCtx) -> usize {
match container {
Container::Little => {
if is_rela { reloc32::SIZEOF_RELA } else { reloc32::SIZEOF_REL }
},
Container::Big => {
if is_rela { reloc64::SIZEOF_RELA } else { reloc64::SIZEOF_REL }
}
}
}
}
impl<'a> ctx::TryFromCtx<'a, RelocCtx> for Reloc {
type Error = crate::error::Error;
fn try_from_ctx(bytes: &'a [u8], (is_rela, Ctx { container, le }): RelocCtx) -> result::Result<(Self, usize), Self::Error> {
use scroll::Pread;
let reloc = match container {
Container::Little => {
if is_rela {
(bytes.pread_with::<reloc32::Rela>(0, le)?.into(), reloc32::SIZEOF_RELA)
} else {
(bytes.pread_with::<reloc32::Rel>(0, le)?.into(), reloc32::SIZEOF_REL)
}
},
Container::Big => {
if is_rela {
(bytes.pread_with::<reloc64::Rela>(0, le)?.into(), reloc64::SIZEOF_RELA)
} else {
(bytes.pread_with::<reloc64::Rel>(0, le)?.into(), reloc64::SIZEOF_REL)
}
}
};
Ok(reloc)
}
}
impl ctx::TryIntoCtx<RelocCtx> for Reloc {
type Error = crate::error::Error;
/// Writes the relocation into `bytes`
fn try_into_ctx(self, bytes: &mut [u8], (is_rela, Ctx {container, le}): RelocCtx) -> result::Result<usize, Self::Error> {
use scroll::Pwrite;
match container {
Container::Little => {
if is_rela {
let rela: reloc32::Rela = self.into();
Ok(bytes.pwrite_with(rela, 0, le)?)
} else {
let rel: reloc32::Rel = self.into();
Ok(bytes.pwrite_with(rel, 0, le)?)
}
},
Container::Big => {
if is_rela {
let rela: reloc64::Rela = self.into();
Ok(bytes.pwrite_with(rela, 0, le)?)
} else {
let rel: reloc64::Rel = self.into();
Ok(bytes.pwrite_with(rel, 0, le)?)
}
},
}
}
}
impl ctx::IntoCtx<(bool, Ctx)> for Reloc {
/// Writes the relocation into `bytes`
fn into_ctx(self, bytes: &mut [u8], ctx: RelocCtx) {
use scroll::Pwrite;
bytes.pwrite_with(self, 0, ctx).unwrap();
}
}
impl fmt::Debug for Reloc {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.debug_struct("Reloc")
.field("r_offset", &format_args!("{:x}", self.r_offset))
.field("r_addend", &format_args!("{:x}", self.r_addend.unwrap_or(0)))
.field("r_sym", &self.r_sym)
.field("r_type", &self.r_type)
.finish()
}
}
#[derive(Default)]
/// An ELF section containing relocations, allowing lazy iteration over symbols.
pub struct RelocSection<'a> {
bytes: &'a [u8],
count: usize,
ctx: RelocCtx,
start: usize,
end: usize,
}
impl<'a> fmt::Debug for RelocSection<'a> {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
let len = self.bytes.len();
fmt.debug_struct("RelocSection")
.field("bytes", &len)
.field("range", &format!("{:#x}..{:#x}", self.start, self.end))
.field("count", &self.count)
.field("Relocations", &self.to_vec())
.finish()
}
}
impl<'a> RelocSection<'a> {
#[cfg(feature = "endian_fd")]
/// Parse a REL or RELA section of size `filesz` from `offset`.
pub fn parse(bytes: &'a [u8], offset: usize, filesz: usize, is_rela: bool, ctx: Ctx) -> crate::error::Result<RelocSection<'a>> {
// TODO: better error message when too large (see symtab implementation)
let bytes = if filesz != 0 {
bytes.pread_with::<&'a [u8]>(offset, filesz)?
} else {
&[]
};
Ok(RelocSection {
bytes: bytes,
count: filesz / Reloc::size(is_rela, ctx),
ctx: (is_rela, ctx),
start: offset,
end: offset + filesz,
})
}
/// Try to parse a single relocation from the binary, at `index`.
#[inline]
pub fn get(&self, index: usize) -> Option<Reloc> {
if index >= self.count {
None
} else {
Some(self.bytes.pread_with(index * Reloc::size_with(&self.ctx), self.ctx).unwrap())
}
}
/// The number of relocations in the section.
#[inline]
pub fn len(&self) -> usize {
self.count
}
/// Returns true if section has no relocations.
#[inline]
pub fn is_empty(&self) -> bool {
self.count == 0
}
/// Iterate over all relocations.
pub fn iter(&self) -> RelocIterator<'a> {
self.into_iter()
}
/// Parse all relocations into a vector.
pub fn to_vec(&self) -> Vec<Reloc> {
self.iter().collect()
}
}
impl<'a, 'b> IntoIterator for &'b RelocSection<'a> {
type Item = <RelocIterator<'a> as Iterator>::Item;
type IntoIter = RelocIterator<'a>;
#[inline]
fn into_iter(self) -> Self::IntoIter {
RelocIterator {
bytes: self.bytes,
offset: 0,
index: 0,
count: self.count,
ctx: self.ctx,
}
}
}
pub struct RelocIterator<'a> {
bytes: &'a [u8],
offset: usize,
index: usize,
count: usize,
ctx: RelocCtx,
}
impl<'a> fmt::Debug for RelocIterator<'a> {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("RelocIterator")
.field("bytes", &"<... redacted ...>")
.field("offset", &self.offset)
.field("index", &self.index)
.field("count", &self.count)
.field("ctx", &self.ctx)
.finish()
}
}
impl<'a> Iterator for RelocIterator<'a> {
type Item = Reloc;
#[inline]
fn next(&mut self) -> Option<Self::Item> {
if self.index >= self.count {
None
} else {
self.index += 1;
Some(self.bytes.gread_with(&mut self.offset, self.ctx).unwrap())
}
}
}
impl<'a> ExactSizeIterator for RelocIterator<'a> {
#[inline]
fn len(&self) -> usize {
self.count - self.index
}
}
} // end if_alloc
