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Quelle elf.rs
Sprache: unbekannt
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//! This module provides a [`Builder`] for reading, modifying, and then writing ELF files.
use alloc::vec::Vec;
use core::convert::TryInto;
use core::fmt;
use core::marker::PhantomData;
#[cfg(not(feature = "std"))]
use hashbrown::HashMap;
#[cfg(feature = "std")]
use std::collections::HashMap;
use crate::build::{ByteString, Bytes, Error, Id, IdPrivate, Item, Result, Table};
use crate::elf;
use crate::read::elf::{Dyn, FileHeader, ProgramHeader, Rela, SectionHeader, Sym};
use crate::read::{self, FileKind, ReadRef};
use crate::write;
use crate::Endianness;
/// A builder for reading, modifying, and then writing ELF files.
///
/// Public fields are available for modifying the values that will be written.
/// Methods are available to add elements to tables, and elements can be deleted
/// from tables by setting the `delete` field in the element.
#[derive(Debug)]
pub struct Builder<'data> {
/// The endianness.
///
/// Used to set the data encoding when writing the ELF file.
pub endian: Endianness,
/// Whether file is 64-bit.
///
/// Use to set the file class when writing the ELF file.
pub is_64: bool,
/// The alignment of [`elf::PT_LOAD`] segments.
///
/// This is an informational field and is not used when writing the ELF file.
/// It can optionally be used when calling [`Segments::add_load_segment`].
///
/// It is determined heuristically when reading the ELF file. Currently,
/// if all load segments have the same alignment, that alignment is used,
/// otherwise it is set to 1.
pub load_align: u64,
/// The file header.
pub header: Header,
/// The segment table.
pub segments: Segments<'data>,
/// The section table.
pub sections: Sections<'data>,
/// The symbol table.
pub symbols: Symbols<'data>,
/// The dynamic symbol table.
pub dynamic_symbols: DynamicSymbols<'data>,
/// The base version for the GNU version definitions.
///
/// This will be written as a version definition with index 1.
pub version_base: Option<ByteString<'data>>,
/// The GNU version definitions and dependencies.
pub versions: Versions<'data>,
/// The filenames used in the GNU version definitions.
pub version_files: VersionFiles<'data>,
/// The bucket count parameter for the hash table.
pub hash_bucket_count: u32,
/// The bloom shift parameter for the GNU hash table.
pub gnu_hash_bloom_shift: u32,
/// The bloom count parameter for the GNU hash table.
pub gnu_hash_bloom_count: u32,
/// The bucket count parameter for the GNU hash table.
pub gnu_hash_bucket_count: u32,
marker: PhantomData<()>,
}
impl<'data> Builder<'data> {
/// Create a new ELF builder.
pub fn new(endian: Endianness, is_64: bool) -> Self {
Self {
endian,
is_64,
load_align: 1,
header: Header::default(),
segments: Segments::new(),
sections: Sections::new(),
symbols: Symbols::new(),
dynamic_symbols: Symbols::new(),
version_base: None,
versions: Versions::new(),
version_files: VersionFiles::new(),
hash_bucket_count: 0,
gnu_hash_bloom_shift: 0,
gnu_hash_bloom_count: 0,
gnu_hash_bucket_count: 0,
marker: PhantomData,
}
}
/// Read the ELF file from file data.
pub fn read<R: ReadRef<'data>>(data: R) -> Result<Self> {
match FileKind::parse(data)? {
FileKind::Elf32 => Self::read32(data),
FileKind::Elf64 => Self::read64(data),
#[allow(unreachable_patterns)]
_ => Err(Error::new("Not an ELF file")),
}
}
/// Read a 32-bit ELF file from file data.
pub fn read32<R: ReadRef<'data>>(data: R) -> Result<Self> {
Self::read_file::<elf::FileHeader32<Endianness>, R>(data)
}
/// Read a 64-bit ELF file from file data.
pub fn read64<R: ReadRef<'data>>(data: R) -> Result<Self> {
Self::read_file::<elf::FileHeader64<Endianness>, R>(data)
}
fn read_file<Elf, R>(data: R) -> Result<Self>
where
Elf: FileHeader<Endian = Endianness>,
R: ReadRef<'data>,
{
let header = Elf::parse(data)?;
let endian = header.endian()?;
let is_mips64el = header.is_mips64el(endian);
let section_strings_index = header.section_strings_index(endian, data)?;
let segments = header.program_headers(endian, data)?;
let sections = header.sections(endian, data)?;
let symbols = sections.symbols(endian, data, elf::SHT_SYMTAB)?;
let dynamic_symbols = sections.symbols(endian, data, elf::SHT_DYNSYM)?;
let mut builder = Builder {
endian,
is_64: header.is_type_64(),
load_align: 0,
header: Header {
os_abi: header.e_ident().os_abi,
abi_version: header.e_ident().abi_version,
e_type: header.e_type(endian),
e_machine: header.e_machine(endian),
e_entry: header.e_entry(endian).into(),
e_flags: header.e_flags(endian),
e_phoff: header.e_phoff(endian).into(),
},
segments: Segments::new(),
sections: Sections::new(),
symbols: Symbols::new(),
dynamic_symbols: Symbols::new(),
version_base: None,
versions: Versions::new(),
version_files: VersionFiles::new(),
hash_bucket_count: 0,
gnu_hash_bloom_shift: 0,
gnu_hash_bloom_count: 0,
gnu_hash_bucket_count: 0,
marker: PhantomData,
};
for segment in segments {
if segment.p_type(endian) == elf::PT_LOAD {
let p_align = segment.p_align(endian).into();
if builder.load_align == 0 {
builder.load_align = p_align;
} else if builder.load_align != p_align {
builder.load_align = 1;
}
}
let id = builder.segments.next_id();
builder.segments.push(Segment {
id,
delete: false,
p_type: segment.p_type(endian),
p_flags: segment.p_flags(endian),
p_offset: segment.p_offset(endian).into(),
p_vaddr: segment.p_vaddr(endian).into(),
p_paddr: segment.p_paddr(endian).into(),
p_filesz: segment.p_filesz(endian).into(),
p_memsz: segment.p_memsz(endian).into(),
p_align: segment.p_align(endian).into(),
sections: Vec::new(),
marker: PhantomData,
});
}
if builder.load_align == 0 {
builder.load_align = 1;
}
for (index, section) in sections.enumerate().skip(1) {
let id = SectionId(index.0 - 1);
let relocations = if let Some((rels, link)) = section.rel(endian, data)? {
Self::read_relocations(
index,
endian,
is_mips64el,
section,
rels,
link,
&symbols,
&dynamic_symbols,
)?
} else if let Some((rels, link)) = section.rela(endian, data)? {
Self::read_relocations(
index,
endian,
is_mips64el,
section,
rels,
link,
&symbols,
&dynamic_symbols,
)?
} else {
SectionData::Data(Bytes::default())
};
if let Some(hash) = section.hash_header(endian, data)? {
builder.hash_bucket_count = hash.bucket_count.get(endian);
}
if let Some(hash) = section.gnu_hash_header(endian, data)? {
builder.gnu_hash_bloom_shift = hash.bloom_shift.get(endian);
builder.gnu_hash_bloom_count = hash.bloom_count.get(endian);
builder.gnu_hash_bucket_count = hash.bucket_count.get(endian);
}
let data = match section.sh_type(endian) {
elf::SHT_NOBITS => SectionData::UninitializedData(section.sh_size(endian).into()),
elf::SHT_PROGBITS
| elf::SHT_INIT_ARRAY
| elf::SHT_FINI_ARRAY
| elf::SHT_PREINIT_ARRAY => SectionData::Data(section.data(endian, data)?.into()),
elf::SHT_REL | elf::SHT_RELA => relocations,
elf::SHT_SYMTAB => {
if index == symbols.section() {
SectionData::Symbol
} else {
return Err(Error(format!(
"Unsupported SHT_SYMTAB section at index {}",
index
)));
}
}
elf::SHT_SYMTAB_SHNDX => {
if index == symbols.shndx_section() {
SectionData::SymbolSectionIndex
} else {
return Err(Error(format!(
"Unsupported SHT_SYMTAB_SHNDX section at index {}",
index
)));
}
}
elf::SHT_DYNSYM => {
if index == dynamic_symbols.section() {
SectionData::DynamicSymbol
} else {
return Err(Error(format!(
"Unsupported SHT_DYNSYM section at index {}",
index
)));
}
}
elf::SHT_STRTAB => {
if index == symbols.string_section() {
SectionData::String
} else if index == dynamic_symbols.string_section() {
SectionData::DynamicString
} else if index == section_strings_index {
SectionData::SectionString
} else {
return Err(Error(format!(
"Unsupported SHT_STRTAB section at index {}",
index
)));
}
}
elf::SHT_NOTE => SectionData::Note(section.data(endian, data)?.into()),
elf::SHT_DYNAMIC => {
let (dyns, link) = section.dynamic(endian, data)?.unwrap();
let dynamic_strings = sections.strings(endian, data, link)?;
Self::read_dynamics::<Elf, _>(endian, dyns, dynamic_strings)?
}
elf::SHT_GNU_ATTRIBUTES => {
let attributes = section.attributes(endian, data)?;
Self::read_attributes(index, attributes, sections.len(), symbols.len())?
}
elf::SHT_HASH => SectionData::Hash,
elf::SHT_GNU_HASH => SectionData::GnuHash,
elf::SHT_GNU_VERSYM => SectionData::GnuVersym,
elf::SHT_GNU_VERDEF => SectionData::GnuVerdef,
elf::SHT_GNU_VERNEED => SectionData::GnuVerneed,
other => match (builder.header.e_machine, other) {
(elf::EM_ARM, elf::SHT_ARM_ATTRIBUTES)
| (elf::EM_AARCH64, elf::SHT_AARCH64_ATTRIBUTES)
| (elf::EM_CSKY, elf::SHT_CSKY_ATTRIBUTES)
| (elf::EM_RISCV, elf::SHT_RISCV_ATTRIBUTES) => {
let attributes = section.attributes(endian, data)?;
Self::read_attributes(index, attributes, sections.len(), symbols.len())?
}
// Some section types that we can't parse but that are safe to copy.
// Lots of types missing, add as needed. We can't default to copying
// everything because some types are not safe to copy.
(elf::EM_ARM, elf::SHT_ARM_EXIDX)
| (elf::EM_IA_64, elf::SHT_IA_64_UNWIND)
| (elf::EM_MIPS, elf::SHT_MIPS_REGINFO)
| (elf::EM_MIPS, elf::SHT_MIPS_DWARF)
| (elf::EM_X86_64, elf::SHT_X86_64_UNWIND) => {
SectionData::Data(section.data(endian, data)?.into())
}
_ => return Err(Error(format!("Unsupported section type {:x}", other))),
},
};
let sh_flags = section.sh_flags(endian).into();
let sh_link = section.sh_link(endian);
let sh_link_section = if sh_link == 0 {
None
} else {
if sh_link as usize >= sections.len() {
return Err(Error(format!(
"Invalid sh_link {} in section at index {}",
sh_link, index
)));
}
Some(SectionId(sh_link as usize - 1))
};
let sh_info = section.sh_info(endian);
let sh_info_section = if sh_info == 0 || sh_flags & u64::from(elf::SHF_INFO_LINK) == 0 {
None
} else {
if sh_info as usize >= sections.len() {
return Err(Error(format!(
"Invalid sh_info link {} in section at index {}",
sh_info, index
)));
}
Some(SectionId(sh_info as usize - 1))
};
let sh_flags = section.sh_flags(endian).into();
let sh_addr = section.sh_addr(endian).into();
if sh_flags & u64::from(elf::SHF_ALLOC) != 0 {
for segment in &mut builder.segments {
if segment.contains_address(sh_addr) {
segment.sections.push(id);
}
}
}
builder.sections.push(Section {
id,
delete: false,
name: sections.section_name(endian, section)?.into(),
sh_type: section.sh_type(endian),
sh_flags,
sh_addr,
sh_offset: section.sh_offset(endian).into(),
sh_size: section.sh_size(endian).into(),
sh_link_section,
sh_info,
sh_info_section,
sh_addralign: section.sh_addralign(endian).into(),
sh_entsize: section.sh_entsize(endian).into(),
data,
});
}
Self::read_symbols(
endian,
&symbols,
&mut builder.symbols,
builder.sections.len(),
)?;
Self::read_symbols(
endian,
&dynamic_symbols,
&mut builder.dynamic_symbols,
builder.sections.len(),
)?;
builder.read_gnu_versions(endian, data, §ions, &dynamic_symbols)?;
Ok(builder)
}
#[allow(clippy::too_many_arguments)]
fn read_relocations<Elf, Rel, R>(
index: read::SectionIndex,
endian: Elf::Endian,
is_mips64el: bool,
section: &'data Elf::SectionHeader,
rels: &'data [Rel],
link: read::SectionIndex,
symbols: &read::elf::SymbolTable<'data, Elf, R>,
dynamic_symbols: &read::elf::SymbolTable<'data, Elf, R>,
) -> Result<SectionData<'data>>
where
Elf: FileHeader<Endian = Endianness>,
Rel: Copy + Into<Elf::Rela>,
R: ReadRef<'data>,
{
if link == dynamic_symbols.section() {
Self::read_relocations_impl::<Elf, Rel, true>(
index,
endian,
is_mips64el,
rels,
dynamic_symbols.len(),
)
.map(SectionData::DynamicRelocation)
} else if link.0 == 0 || section.sh_flags(endian).into() & u64::from(elf::SHF_ALLOC) != 0 {
// If there's no link, then none of the relocations may reference symbols.
// Assume that these are dynamic relocations, but don't use the dynamic
// symbol table when parsing.
//
// Additionally, sometimes there is an allocated section that links to
// the static symbol table. We don't currently support this case in general,
// but if none of the relocation entries reference a symbol then it is
// safe to treat it as a dynamic relocation section.
//
// For both of these cases, if there is a reference to a symbol then
// an error will be returned when parsing the relocations.
Self::read_relocations_impl::<Elf, Rel, true>(index, endian, is_mips64el, rels, 0)
.map(SectionData::DynamicRelocation)
} else if link == symbols.section() {
Self::read_relocations_impl::<Elf, Rel, false>(
index,
endian,
is_mips64el,
rels,
symbols.len(),
)
.map(SectionData::Relocation)
} else {
return Err(Error(format!(
"Invalid sh_link {} in relocation section at index {}",
link.0, index,
)));
}
}
fn read_relocations_impl<Elf, Rel, const DYNAMIC: bool>(
index: read::SectionIndex,
endian: Elf::Endian,
is_mips64el: bool,
rels: &'data [Rel],
symbols_len: usize,
) -> Result<Vec<Relocation<DYNAMIC>>>
where
Elf: FileHeader<Endian = Endianness>,
Rel: Copy + Into<Elf::Rela>,
{
let mut relocations = Vec::new();
for rel in rels {
let rel = (*rel).into();
let symbol = if let Some(symbol) = rel.symbol(endian, is_mips64el) {
if symbol.0 >= symbols_len {
return Err(Error(format!(
"Invalid symbol index {} in relocation section at index {}",
symbol, index,
)));
}
Some(SymbolId(symbol.0 - 1))
} else {
None
};
relocations.push(Relocation {
r_offset: rel.r_offset(endian).into(),
symbol,
r_type: rel.r_type(endian, is_mips64el),
r_addend: rel.r_addend(endian).into(),
});
}
Ok(relocations)
}
fn read_dynamics<Elf, R>(
endian: Elf::Endian,
dyns: &'data [Elf::Dyn],
strings: read::StringTable<'data, R>,
) -> Result<SectionData<'data>>
where
Elf: FileHeader<Endian = Endianness>,
R: ReadRef<'data>,
{
let mut dynamics = Vec::with_capacity(dyns.len());
for d in dyns {
let tag = d.d_tag(endian).into().try_into().map_err(|_| {
Error(format!(
"Unsupported dynamic tag 0x{:x}",
d.d_tag(endian).into()
))
})?;
if tag == elf::DT_NULL {
break;
}
let val = d.d_val(endian).into();
dynamics.push(if d.is_string(endian) {
let val =
strings
.get(val.try_into().map_err(|_| {
Error(format!("Unsupported dynamic string 0x{:x}", val))
})?)
.map_err(|_| Error(format!("Invalid dynamic string 0x{:x}", val)))?;
Dynamic::String {
tag,
val: val.into(),
}
} else {
match tag {
elf::DT_SYMTAB
| elf::DT_STRTAB
| elf::DT_STRSZ
| elf::DT_HASH
| elf::DT_GNU_HASH
| elf::DT_VERSYM
| elf::DT_VERDEF
| elf::DT_VERDEFNUM
| elf::DT_VERNEED
| elf::DT_VERNEEDNUM => Dynamic::Auto { tag },
_ => Dynamic::Integer { tag, val },
}
});
}
Ok(SectionData::Dynamic(dynamics))
}
fn read_symbols<Elf, R, const DYNAMIC: bool>(
endian: Elf::Endian,
symbols: &read::elf::SymbolTable<'data, Elf, R>,
builder_symbols: &mut Symbols<'data, DYNAMIC>,
sections_len: usize,
) -> Result<()>
where
Elf: FileHeader<Endian = Endianness>,
R: ReadRef<'data>,
{
for (index, symbol) in symbols.enumerate().skip(1) {
let id = SymbolId(index.0 - 1);
let section =
if let Some(section_index) = symbols.symbol_section(endian, symbol, index)? {
let section_id = section_index.0.wrapping_sub(1);
if section_id >= sections_len {
return Err(Error::new("Invalid symbol section index"));
}
Some(SectionId(section_id))
} else {
None
};
builder_symbols.push(Symbol {
id,
delete: false,
name: symbols.symbol_name(endian, symbol)?.into(),
section,
st_info: symbol.st_info(),
st_other: symbol.st_other(),
st_shndx: symbol.st_shndx(endian),
st_value: symbol.st_value(endian).into(),
st_size: symbol.st_size(endian).into(),
version: VersionId::local(),
version_hidden: false,
});
}
Ok(())
}
fn read_attributes<Elf>(
index: read::SectionIndex,
attributes: read::elf::AttributesSection<'data, Elf>,
sections_len: usize,
symbols_len: usize,
) -> Result<SectionData<'data>>
where
Elf: FileHeader<Endian = Endianness>,
{
let mut builder_attributes = AttributesSection::new();
let mut subsections = attributes.subsections()?;
while let Some(subsection) = subsections.next()? {
let mut builder_subsection = AttributesSubsection::new(subsection.vendor().into());
let mut subsubsections = subsection.subsubsections();
while let Some(subsubsection) = subsubsections.next()? {
let tag = match subsubsection.tag() {
elf::Tag_File => AttributeTag::File,
elf::Tag_Section => {
let mut tag_sections = Vec::new();
let mut indices = subsubsection.indices();
while let Some(index) = indices.next()? {
let index = index as usize;
if index >= sections_len {
return Err(Error(format!(
"Invalid section index {} in attribute",
index
)));
}
tag_sections.push(SectionId(index - 1));
}
AttributeTag::Section(tag_sections)
}
elf::Tag_Symbol => {
let mut tag_symbols = Vec::new();
let mut indices = subsubsection.indices();
while let Some(index) = indices.next()? {
let index = index as usize;
if index >= symbols_len {
return Err(Error(format!(
"Invalid symbol index {} in attribute",
index
)));
}
tag_symbols.push(SymbolId(index - 1));
}
AttributeTag::Symbol(tag_symbols)
}
tag => {
return Err(Error(format!(
"Unsupported attribute tag 0x{:x} in section at index {}",
tag, index,
)))
}
};
let data = subsubsection.attributes_data().into();
builder_subsection
.subsubsections
.push(AttributesSubsubsection { tag, data });
}
builder_attributes.subsections.push(builder_subsection);
}
Ok(SectionData::Attributes(builder_attributes))
}
fn read_gnu_versions<Elf, R>(
&mut self,
endian: Elf::Endian,
data: R,
sections: &read::elf::SectionTable<'data, Elf, R>,
dynamic_symbols: &read::elf::SymbolTable<'data, Elf, R>,
) -> Result<()>
where
Elf: FileHeader<Endian = Endianness>,
R: ReadRef<'data>,
{
let strings = dynamic_symbols.strings();
let mut ids = HashMap::new();
ids.insert(0, VersionId::local());
ids.insert(1, VersionId::global());
if let Some((mut verdefs, link)) = sections.gnu_verdef(endian, data)? {
if link != dynamic_symbols.string_section() {
return Err(Error::new("Invalid SHT_GNU_VERDEF section"));
}
while let Some((verdef, mut verdauxs)) = verdefs.next()? {
let flags = verdef.vd_flags.get(endian);
if flags & elf::VER_FLG_BASE != 0 {
if flags != elf::VER_FLG_BASE
|| verdef.vd_ndx.get(endian) != 1
|| verdef.vd_cnt.get(endian) != 1
{
return Err(Error::new("Unsupported VER_FLG_BASE in SHT_GNU_VERDEF"));
}
if self.version_base.is_some() {
return Err(Error::new("Duplicate VER_FLG_BASE in SHT_GNU_VERDEF"));
}
let verdaux = verdauxs.next()?.ok_or_else(|| {
Error::new("Missing name for VER_FLG_BASE in SHT_GNU_VERDEF")
})?;
self.version_base = Some(verdaux.name(endian, strings)?.into());
continue;
}
let index = verdef.vd_ndx.get(endian) & elf::VERSYM_VERSION;
let id = self.versions.next_id();
if ids.insert(index, id).is_some() {
return Err(Error(format!("Duplicate SHT_GNU_VERDEF index {}", index)));
}
let mut names = Vec::new();
while let Some(verdaux) = verdauxs.next()? {
names.push(verdaux.name(endian, strings)?.into());
}
let data = VersionData::Def(VersionDef { flags, names });
self.versions.push(Version {
id,
delete: false,
data,
});
}
}
if let Some((mut verneeds, link)) = sections.gnu_verneed(endian, data)? {
if link != dynamic_symbols.string_section() {
return Err(Error::new("Invalid SHT_GNU_VERNEED section"));
}
while let Some((verneed, mut vernauxs)) = verneeds.next()? {
let file = VersionFileId(self.version_files.len());
self.version_files.push(VersionFile {
id: file,
delete: false,
name: verneed.file(endian, strings)?.into(),
});
while let Some(vernaux) = vernauxs.next()? {
let index = vernaux.vna_other.get(endian) & elf::VERSYM_VERSION;
let id = self.versions.next_id();
if ids.insert(index, id).is_some() {
return Err(Error(format!("Duplicate SHT_GNU_VERNEED index {}", index)));
}
let data = VersionData::Need(VersionNeed {
flags: vernaux.vna_flags.get(endian),
name: vernaux.name(endian, strings)?.into(),
file,
});
self.versions.push(Version {
id,
delete: false,
data,
});
}
}
}
if let Some((versyms, link)) = sections.gnu_versym(endian, data)? {
if versyms.len() != dynamic_symbols.len() || link != dynamic_symbols.section() {
return Err(Error::new("Invalid SHT_GNU_VERSYM section"));
}
for (id, versym) in versyms.iter().skip(1).enumerate() {
let index = versym.0.get(endian);
let symbol = self.dynamic_symbols.get_mut(SymbolId(id));
symbol.version = *ids
.get(&(index & elf::VERSYM_VERSION))
.ok_or_else(|| Error(format!("Invalid SHT_GNU_VERSYM index {:x}", index)))?;
symbol.version_hidden = index & elf::VERSYM_HIDDEN != 0;
}
}
Ok(())
}
/// Write the ELF file to the buffer.
pub fn write(mut self, buffer: &mut dyn write::WritableBuffer) -> Result<()> {
struct SectionOut {
id: SectionId,
name: Option<write::StringId>,
offset: usize,
attributes: Vec<u8>,
}
struct SymbolOut {
id: SymbolId,
name: Option<write::StringId>,
}
struct DynamicSymbolOut {
id: DynamicSymbolId,
name: Option<write::StringId>,
hash: Option<u32>,
gnu_hash: Option<u32>,
}
#[derive(Default, Clone)]
struct VersionFileOut {
versions: Vec<VersionId>,
}
// TODO: require the caller to do this?
self.delete_orphans();
self.delete_unused_versions();
let mut writer = write::elf::Writer::new(self.endian, self.is_64, buffer);
// Find metadata sections, and assign section indices.
let mut shstrtab_id = None;
let mut symtab_id = None;
let mut symtab_shndx_id = None;
let mut strtab_id = None;
let mut dynsym_id = None;
let mut dynstr_id = None;
let mut hash_id = None;
let mut gnu_hash_id = None;
let mut gnu_versym_id = None;
let mut gnu_verdef_id = None;
let mut gnu_verneed_id = None;
let mut out_sections = Vec::with_capacity(self.sections.len());
let mut out_sections_index = vec![None; self.sections.len()];
if !self.sections.is_empty() {
writer.reserve_null_section_index();
}
for section in &self.sections {
let index = match §ion.data {
SectionData::Data(_)
| SectionData::UninitializedData(_)
| SectionData::Relocation(_)
| SectionData::DynamicRelocation(_)
| SectionData::Note(_)
| SectionData::Dynamic(_)
| SectionData::Attributes(_) => writer.reserve_section_index(),
SectionData::SectionString => {
if shstrtab_id.is_some() {
return Err(Error::new("Multiple .shstrtab sections"));
}
shstrtab_id = Some(section.id);
writer.reserve_shstrtab_section_index_with_name(§ion.name)
}
SectionData::Symbol => {
if symtab_id.is_some() {
return Err(Error::new("Multiple .symtab sections"));
}
symtab_id = Some(section.id);
writer.reserve_symtab_section_index_with_name(§ion.name)
}
SectionData::SymbolSectionIndex => {
if symtab_shndx_id.is_some() {
return Err(Error::new("Multiple .symtab_shndx sections"));
}
symtab_shndx_id = Some(section.id);
writer.reserve_symtab_shndx_section_index_with_name(§ion.name)
}
SectionData::String => {
if strtab_id.is_some() {
return Err(Error::new("Multiple .strtab sections"));
}
strtab_id = Some(section.id);
writer.reserve_strtab_section_index_with_name(§ion.name)
}
SectionData::DynamicSymbol => {
if dynsym_id.is_some() {
return Err(Error::new("Multiple .dynsym sections"));
}
dynsym_id = Some(section.id);
writer.reserve_dynsym_section_index_with_name(§ion.name)
}
SectionData::DynamicString => {
if dynstr_id.is_some() {
return Err(Error::new("Multiple .dynstr sections"));
}
dynstr_id = Some(section.id);
writer.reserve_dynstr_section_index_with_name(§ion.name)
}
SectionData::Hash => {
if hash_id.is_some() {
return Err(Error::new("Multiple .hash sections"));
}
hash_id = Some(section.id);
writer.reserve_hash_section_index_with_name(§ion.name)
}
SectionData::GnuHash => {
if gnu_hash_id.is_some() {
return Err(Error::new("Multiple .gnu.hash sections"));
}
gnu_hash_id = Some(section.id);
writer.reserve_gnu_hash_section_index_with_name(§ion.name)
}
SectionData::GnuVersym => {
if gnu_versym_id.is_some() {
return Err(Error::new("Multiple .gnu.version sections"));
}
gnu_versym_id = Some(section.id);
writer.reserve_gnu_versym_section_index_with_name(§ion.name)
}
SectionData::GnuVerdef => {
if gnu_verdef_id.is_some() {
return Err(Error::new("Multiple .gnu.version_d sections"));
}
gnu_verdef_id = Some(section.id);
writer.reserve_gnu_verdef_section_index_with_name(§ion.name)
}
SectionData::GnuVerneed => {
if gnu_verneed_id.is_some() {
return Err(Error::new("Multiple .gnu.version_r sections"));
}
gnu_verneed_id = Some(section.id);
writer.reserve_gnu_verneed_section_index_with_name(§ion.name)
}
};
out_sections_index[section.id.0] = Some(index);
let name = if section.name.is_empty() {
None
} else {
Some(writer.add_section_name(§ion.name))
};
out_sections.push(SectionOut {
id: section.id,
name,
offset: 0,
attributes: Vec::new(),
});
}
// Assign dynamic strings.
for section in &self.sections {
if let SectionData::Dynamic(dynamics) = §ion.data {
for dynamic in dynamics {
if let Dynamic::String { val, .. } = dynamic {
writer.add_dynamic_string(val);
}
}
}
}
// Assign dynamic symbol indices.
let mut out_dynsyms = Vec::with_capacity(self.dynamic_symbols.len());
// Local symbols must come before global.
let local_symbols = self
.dynamic_symbols
.into_iter()
.filter(|symbol| symbol.st_bind() == elf::STB_LOCAL);
let global_symbols = self
.dynamic_symbols
.into_iter()
.filter(|symbol| symbol.st_bind() != elf::STB_LOCAL);
for symbol in local_symbols.chain(global_symbols) {
let mut name = None;
let mut hash = None;
let mut gnu_hash = None;
if !symbol.name.is_empty() {
name = Some(writer.add_dynamic_string(&symbol.name));
if hash_id.is_some() {
hash = Some(elf::hash(&symbol.name));
}
if gnu_hash_id.is_some()
&& (symbol.section.is_some() || symbol.st_shndx != elf::SHN_UNDEF)
{
gnu_hash = Some(elf::gnu_hash(&symbol.name));
}
}
out_dynsyms.push(DynamicSymbolOut {
id: symbol.id,
name,
hash,
gnu_hash,
});
}
let num_local_dynamic = out_dynsyms
.iter()
.take_while(|sym| self.dynamic_symbols.get(sym.id).st_bind() == elf::STB_LOCAL)
.count();
// We must sort for GNU hash before allocating symbol indices.
let mut gnu_hash_symbol_count = 0;
if gnu_hash_id.is_some() {
if self.gnu_hash_bucket_count == 0 {
return Err(Error::new(".gnu.hash bucket count is zero"));
}
// TODO: recalculate bucket_count?
out_dynsyms[num_local_dynamic..].sort_by_key(|sym| match sym.gnu_hash {
None => (0, 0),
Some(hash) => (1, hash % self.gnu_hash_bucket_count),
});
gnu_hash_symbol_count = out_dynsyms
.iter()
.skip(num_local_dynamic)
.skip_while(|sym| sym.gnu_hash.is_none())
.count() as u32;
}
let mut out_dynsyms_index = vec![None; self.dynamic_symbols.len()];
if dynsym_id.is_some() {
writer.reserve_null_dynamic_symbol_index();
}
for out_dynsym in &mut out_dynsyms {
out_dynsyms_index[out_dynsym.id.0] = Some(writer.reserve_dynamic_symbol_index());
}
// Hash parameters.
let hash_index_base = 1; // Null symbol.
let hash_chain_count = hash_index_base + out_dynsyms.len() as u32;
// GNU hash parameters.
let gnu_hash_index_base = if gnu_hash_symbol_count == 0 {
0
} else {
out_dynsyms.len() as u32 - gnu_hash_symbol_count
};
let gnu_hash_symbol_base = gnu_hash_index_base + 1; // Null symbol.
// Assign symbol indices.
let mut out_syms = Vec::with_capacity(self.symbols.len());
// Local symbols must come before global.
let local_symbols = self
.symbols
.into_iter()
.filter(|symbol| symbol.st_bind() == elf::STB_LOCAL);
let global_symbols = self
.symbols
.into_iter()
.filter(|symbol| symbol.st_bind() != elf::STB_LOCAL);
for symbol in local_symbols.chain(global_symbols) {
let name = if symbol.name.is_empty() {
None
} else {
Some(writer.add_string(&symbol.name))
};
out_syms.push(SymbolOut {
id: symbol.id,
name,
});
}
let num_local = out_syms
.iter()
.take_while(|sym| self.symbols.get(sym.id).st_bind() == elf::STB_LOCAL)
.count();
let mut out_syms_index = vec![None; self.symbols.len()];
if symtab_id.is_some() {
writer.reserve_null_symbol_index();
}
for out_sym in out_syms.iter_mut() {
out_syms_index[out_sym.id.0] = Some(writer.reserve_symbol_index(None));
}
// Count the versions and add version strings.
let mut verdef_count = 0;
let mut verdaux_count = 0;
let mut verdef_shared_base = false;
let mut verneed_count = 0;
let mut vernaux_count = 0;
let mut out_version_files = vec![VersionFileOut::default(); self.version_files.len()];
if let Some(version_base) = &self.version_base {
verdef_count += 1;
verdaux_count += 1;
writer.add_dynamic_string(version_base);
}
for version in &self.versions {
match &version.data {
VersionData::Def(def) => {
if def.is_shared(verdef_count, self.version_base.as_ref()) {
verdef_shared_base = true;
} else {
verdaux_count += def.names.len();
for name in &def.names {
writer.add_dynamic_string(name);
}
}
verdef_count += 1;
}
VersionData::Need(need) => {
vernaux_count += 1;
writer.add_dynamic_string(&need.name);
out_version_files[need.file.0].versions.push(version.id);
}
}
}
for file in &self.version_files {
verneed_count += 1;
writer.add_dynamic_string(&file.name);
}
// Build the attributes sections.
for out_section in &mut out_sections {
let SectionData::Attributes(attributes) = &self.sections.get(out_section.id).data
else {
continue;
};
if attributes.subsections.is_empty() {
continue;
}
let mut writer = writer.attributes_writer();
for subsection in &attributes.subsections {
writer.start_subsection(&subsection.vendor);
for subsubsection in &subsection.subsubsections {
writer.start_subsubsection(subsubsection.tag.tag());
match &subsubsection.tag {
AttributeTag::File => {}
AttributeTag::Section(sections) => {
for id in sections {
if let Some(index) = out_sections_index[id.0] {
writer.write_subsubsection_index(index.0);
}
}
writer.write_subsubsection_index(0);
}
AttributeTag::Symbol(symbols) => {
for id in symbols {
if let Some(index) = out_syms_index[id.0] {
writer.write_subsubsection_index(index.0);
}
}
writer.write_subsubsection_index(0);
}
}
writer.write_subsubsection_attributes(&subsubsection.data);
writer.end_subsubsection();
}
writer.end_subsection();
}
out_section.attributes = writer.data();
}
// TODO: support section headers in strtab
if shstrtab_id.is_none() && !out_sections.is_empty() {
return Err(Error::new(".shstrtab section is needed but not present"));
}
if symtab_id.is_none() && !out_syms.is_empty() {
return Err(Error::new(".symtab section is needed but not present"));
}
if symtab_shndx_id.is_none() && writer.symtab_shndx_needed() {
return Err(Error::new(
".symtab.shndx section is needed but not present",
));
} else if symtab_shndx_id.is_some() {
writer.require_symtab_shndx();
}
if strtab_id.is_none() && writer.strtab_needed() {
return Err(Error::new(".strtab section is needed but not present"));
} else if strtab_id.is_some() {
writer.require_strtab();
}
if dynsym_id.is_none() && !out_dynsyms.is_empty() {
return Err(Error::new(".dynsym section is needed but not present"));
}
if dynstr_id.is_none() && writer.dynstr_needed() {
return Err(Error::new(".dynstr section is needed but not present"));
} else if dynstr_id.is_some() {
writer.require_dynstr();
}
if gnu_verdef_id.is_none() && verdef_count > 0 {
return Err(Error::new(
".gnu.version_d section is needed but not present",
));
}
if gnu_verneed_id.is_none() && verneed_count > 0 {
return Err(Error::new(
".gnu.version_r section is needed but not present",
));
}
// Start reserving file ranges.
writer.reserve_file_header();
let mut dynsym_addr = None;
let mut dynstr_addr = None;
let mut hash_addr = None;
let mut gnu_hash_addr = None;
let mut versym_addr = None;
let mut verdef_addr = None;
let mut verneed_addr = None;
if !self.segments.is_empty() {
// TODO: support program headers in other locations.
if self.header.e_phoff != writer.reserved_len() as u64 {
return Err(Error(format!(
"Unsupported e_phoff value 0x{:x}",
self.header.e_phoff
)));
}
writer.reserve_program_headers(self.segments.count() as u32);
}
let mut alloc_sections = Vec::new();
if !self.segments.is_empty() {
// Reserve alloc sections at original offsets.
alloc_sections = out_sections
.iter()
.enumerate()
.filter_map(|(index, out_section)| {
let section = self.sections.get(out_section.id);
if section.is_alloc() {
Some(index)
} else {
None
}
})
.collect();
// The data for alloc sections may need to be written in a different order
// from their section headers.
alloc_sections.sort_by_key(|index| {
let section = &self.sections.get(out_sections[*index].id);
// Empty sections need to come before other sections at the same offset.
(section.sh_offset, section.sh_size)
});
for index in &alloc_sections {
let out_section = &mut out_sections[*index];
let section = &self.sections.get(out_section.id);
if section.sh_type == elf::SHT_NOBITS {
// sh_offset is meaningless for SHT_NOBITS, so preserve the input
// value without checking it.
out_section.offset = section.sh_offset as usize;
continue;
}
if section.sh_offset < writer.reserved_len() as u64 {
return Err(Error(format!(
"Unsupported sh_offset value 0x{:x} for section '{}', expected at least 0x{:x}",
section.sh_offset,
section.name,
writer.reserved_len(),
)));
}
// The input sh_offset needs to be preserved so that offsets in program
// headers are correct.
writer.reserve_until(section.sh_offset as usize);
out_section.offset = match §ion.data {
SectionData::Data(data) => {
writer.reserve(data.len(), section.sh_addralign as usize)
}
SectionData::DynamicRelocation(relocations) => writer
.reserve_relocations(relocations.len(), section.sh_type == elf::SHT_RELA),
SectionData::Note(data) => {
writer.reserve(data.len(), section.sh_addralign as usize)
}
SectionData::Dynamic(dynamics) => writer.reserve_dynamics(1 + dynamics.len()),
SectionData::DynamicSymbol => {
dynsym_addr = Some(section.sh_addr);
writer.reserve_dynsym()
}
SectionData::DynamicString => {
dynstr_addr = Some(section.sh_addr);
writer.reserve_dynstr()
}
SectionData::Hash => {
hash_addr = Some(section.sh_addr);
writer.reserve_hash(self.hash_bucket_count, hash_chain_count)
}
SectionData::GnuHash => {
gnu_hash_addr = Some(section.sh_addr);
writer.reserve_gnu_hash(
self.gnu_hash_bloom_count,
self.gnu_hash_bucket_count,
gnu_hash_symbol_count,
)
}
SectionData::GnuVersym => {
versym_addr = Some(section.sh_addr);
writer.reserve_gnu_versym()
}
SectionData::GnuVerdef => {
verdef_addr = Some(section.sh_addr);
writer.reserve_gnu_verdef(verdef_count, verdaux_count)
}
SectionData::GnuVerneed => {
verneed_addr = Some(section.sh_addr);
writer.reserve_gnu_verneed(verneed_count, vernaux_count)
}
_ => {
return Err(Error(format!(
"Unsupported alloc section type {:x} for section '{}'",
section.sh_type, section.name,
)));
}
};
if out_section.offset as u64 != section.sh_offset {
return Err(Error(format!(
"Unaligned sh_offset value 0x{:x} for section '{}', expected 0x{:x}",
section.sh_offset, section.name, out_section.offset,
)));
}
}
}
// Reserve non-alloc sections at any offset.
for out_section in &mut out_sections {
let section = self.sections.get(out_section.id);
if !self.segments.is_empty() && section.is_alloc() {
continue;
}
out_section.offset = match §ion.data {
SectionData::Data(data) => {
writer.reserve(data.len(), section.sh_addralign as usize)
}
SectionData::UninitializedData(_) => writer.reserved_len(),
SectionData::Note(data) => {
writer.reserve(data.len(), section.sh_addralign as usize)
}
SectionData::Attributes(_) => {
writer.reserve(out_section.attributes.len(), section.sh_addralign as usize)
}
// These are handled elsewhere.
SectionData::Relocation(_)
| SectionData::SectionString
| SectionData::Symbol
| SectionData::SymbolSectionIndex
| SectionData::String => {
continue;
}
_ => {
return Err(Error(format!(
"Unsupported non-alloc section type {:x}",
section.sh_type
)));
}
};
}
writer.reserve_symtab();
writer.reserve_symtab_shndx();
writer.reserve_strtab();
// Reserve non-alloc relocations.
for out_section in &mut out_sections {
let section = self.sections.get(out_section.id);
if !self.segments.is_empty() && section.is_alloc() {
continue;
}
let SectionData::Relocation(relocations) = §ion.data else {
continue;
};
out_section.offset =
writer.reserve_relocations(relocations.len(), section.sh_type == elf::SHT_RELA);
}
writer.reserve_shstrtab();
writer.reserve_section_headers();
// Start writing.
writer.write_file_header(&write::elf::FileHeader {
os_abi: self.header.os_abi,
abi_version: self.header.abi_version,
e_type: self.header.e_type,
e_machine: self.header.e_machine,
e_entry: self.header.e_entry,
e_flags: self.header.e_flags,
})?;
if !self.segments.is_empty() {
writer.write_align_program_headers();
for segment in &self.segments {
writer.write_program_header(&write::elf::ProgramHeader {
p_type: segment.p_type,
p_flags: segment.p_flags,
p_offset: segment.p_offset,
p_vaddr: segment.p_vaddr,
p_paddr: segment.p_paddr,
p_filesz: segment.p_filesz,
p_memsz: segment.p_memsz,
p_align: segment.p_align,
});
}
}
// Write alloc sections.
if !self.segments.is_empty() {
for index in &alloc_sections {
let out_section = &mut out_sections[*index];
let section = self.sections.get(out_section.id);
if section.sh_type == elf::SHT_NOBITS {
continue;
}
writer.pad_until(out_section.offset);
match §ion.data {
SectionData::Data(data) => {
writer.write(data);
}
SectionData::DynamicRelocation(relocations) => {
for rel in relocations {
let r_sym = if let Some(symbol) = rel.symbol {
out_dynsyms_index[symbol.0].unwrap().0
} else {
0
};
writer.write_relocation(
section.sh_type == elf::SHT_RELA,
&write::elf::Rel {
r_offset: rel.r_offset,
r_sym,
r_type: rel.r_type,
r_addend: rel.r_addend,
},
);
}
}
SectionData::Note(data) => {
writer.write(data);
}
SectionData::Dynamic(dynamics) => {
for d in dynamics {
match *d {
Dynamic::Auto { tag } => {
// TODO: support more values
let val = match tag {
elf::DT_SYMTAB => dynsym_addr.ok_or(Error::new(
"Missing .dynsym section for DT_SYMTAB",
))?,
elf::DT_STRTAB => dynstr_addr.ok_or(Error::new(
"Missing .dynstr section for DT_STRTAB",
))?,
elf::DT_STRSZ => writer.dynstr_len() as u64,
elf::DT_HASH => hash_addr.ok_or(Error::new(
"Missing .hash section for DT_HASH",
))?,
elf::DT_GNU_HASH => gnu_hash_addr.ok_or(Error::new(
"Missing .gnu.hash section for DT_GNU_HASH",
))?,
elf::DT_VERSYM => versym_addr.ok_or(Error::new(
"Missing .gnu.version section for DT_VERSYM",
))?,
elf::DT_VERDEF => verdef_addr.ok_or(Error::new(
"Missing .gnu.version_d section for DT_VERDEF",
))?,
elf::DT_VERDEFNUM => verdef_count as u64,
elf::DT_VERNEED => verneed_addr.ok_or(Error::new(
"Missing .gnu.version_r section for DT_VERNEED",
))?,
elf::DT_VERNEEDNUM => verneed_count as u64,
_ => {
return Err(Error(format!(
"Cannot generate value for dynamic tag 0x{:x}",
tag
)))
}
};
writer.write_dynamic(tag, val);
}
Dynamic::Integer { tag, val } => {
writer.write_dynamic(tag, val);
}
Dynamic::String { tag, ref val } => {
let val = writer.get_dynamic_string(val);
writer.write_dynamic_string(tag, val);
}
}
}
writer.write_dynamic(elf::DT_NULL, 0);
}
SectionData::DynamicSymbol => {
writer.write_null_dynamic_symbol();
for out_dynsym in &out_dynsyms {
let symbol = self.dynamic_symbols.get(out_dynsym.id);
let section =
symbol.section.map(|id| out_sections_index[id.0].unwrap());
writer.write_dynamic_symbol(&write::elf::Sym {
name: out_dynsym.name,
section,
st_info: symbol.st_info,
st_other: symbol.st_other,
st_shndx: symbol.st_shndx,
st_value: symbol.st_value,
st_size: symbol.st_size,
});
}
}
SectionData::DynamicString => {
writer.write_dynstr();
}
SectionData::Hash => {
if self.hash_bucket_count == 0 {
return Err(Error::new(".hash bucket count is zero"));
}
writer.write_hash(self.hash_bucket_count, hash_chain_count, |index| {
out_dynsyms
.get(index.checked_sub(hash_index_base)? as usize)?
.hash
});
}
SectionData::GnuHash => {
if self.gnu_hash_bucket_count == 0 {
return Err(Error::new(".gnu.hash bucket count is zero"));
}
writer.write_gnu_hash(
gnu_hash_symbol_base,
self.gnu_hash_bloom_shift,
self.gnu_hash_bloom_count,
self.gnu_hash_bucket_count,
gnu_hash_symbol_count,
|index| {
out_dynsyms[(gnu_hash_index_base + index) as usize]
.gnu_hash
.unwrap()
},
);
}
SectionData::GnuVersym => {
writer.write_null_gnu_versym();
for out_dynsym in &out_dynsyms {
let symbol = self.dynamic_symbols.get(out_dynsym.id);
let mut index = symbol.version.0 as u16;
if symbol.version_hidden {
index |= elf::VERSYM_HIDDEN;
}
writer.write_gnu_versym(index);
}
}
SectionData::GnuVerdef => {
writer.write_align_gnu_verdef();
if let Some(version_base) = &self.version_base {
let verdef = write::elf::Verdef {
version: elf::VER_DEF_CURRENT,
flags: elf::VER_FLG_BASE,
index: 1,
aux_count: 1,
name: writer.get_dynamic_string(version_base),
};
if verdef_shared_base {
writer.write_gnu_verdef_shared(&verdef);
} else {
writer.write_gnu_verdef(&verdef);
}
}
for version in &self.versions {
if let VersionData::Def(def) = &version.data {
let mut names = def.names.iter();
let name = names.next().ok_or_else(|| {
Error(format!("Missing SHT_GNU_VERDEF name {}", version.id.0))
})?;
writer.write_gnu_verdef(&write::elf::Verdef {
version: elf::VER_DEF_CURRENT,
flags: def.flags,
index: version.id.0 as u16,
aux_count: def.names.len() as u16,
name: writer.get_dynamic_string(name),
});
for name in names {
writer.write_gnu_verdaux(writer.get_dynamic_string(name));
}
}
}
}
SectionData::GnuVerneed => {
writer.write_align_gnu_verneed();
for file in &self.version_files {
let out_file = &out_version_files[file.id.0];
if out_file.versions.is_empty() {
continue;
}
writer.write_gnu_verneed(&write::elf::Verneed {
version: elf::VER_NEED_CURRENT,
aux_count: out_file.versions.len() as u16,
file: writer.get_dynamic_string(&file.name),
});
for id in &out_file.versions {
let version = self.versions.get(*id);
// This will always match.
if let VersionData::Need(need) = &version.data {
debug_assert_eq!(*id, version.id);
writer.write_gnu_vernaux(&write::elf::Vernaux {
flags: need.flags,
index: version.id.0 as u16,
name: writer.get_dynamic_string(&need.name),
});
}
}
}
}
_ => {
return Err(Error(format!(
"Unsupported alloc section type {:x}",
section.sh_type
)));
--> --------------------
--> maximum size reached
--> --------------------
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2026-04-04
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