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create a dummy elf .so from scratch

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Folkert 2022-09-04 16:17:32 +02:00
parent e79543aac7
commit c46f8a0073
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400
crates/linker/src/generate_dylib/elf64.rs
View file

@ -1,122 +1,4 @@
use object::elf::{self, SectionHeader64};
use object::read::elf::{FileHeader, ProgramHeader, SectionHeader, Sym};
use object::Endianness;
use object::write::elf::Writer;
// index of the dynamic section
const DYMAMIC_SECTION: usize = 4;
#[derive(Debug)]
struct Dynamic {
tag: u32,
// Ignored if `string` is set.
val: u64,
string: Option<object::write::StringId>,
}
#[derive(Debug)]
struct Symbol {
in_sym: usize,
name: Option<object::write::StringId>,
}
#[derive(Debug)]
struct DynamicSymbol {
in_sym: usize,
name: Option<object::write::StringId>,
section: Option<object::write::elf::SectionIndex>,
gnu_hash: Option<u32>,
}
type Section = SectionHeader64<object::Endianness>;
struct Sections {
hash: Section,
gnu_hash: Section,
dynsym: Section,
dynstr: Section,
dynamic: Section,
}
#[derive(Default)]
struct Addresses {
hash: u64,
gnu_hash: u64,
dynsym: u64,
dynstr: u64,
dynamic: u64,
}
impl Sections {
fn reserve_alloc_sections(
&self,
writer: &mut Writer,
hash_chain_count: u32,
gnu_hash_symbol_count: u32,
dynamic_count: usize,
) -> ([usize; 5], Addresses) {
let sections = self;
let endian = Endianness::Little;
let mut offsets = [0; 5];
let mut extra_offset: usize = 0;
let mut addresses = Addresses::default();
for (i, out_offset) in offsets.iter_mut().enumerate() {
// symtab, strtab and shstrtab is ignored because they are not ALLOC
let in_section = match i {
0 => sections.hash,
1 => sections.gnu_hash,
2 => sections.dynsym,
3 => sections.dynstr,
4 => sections.dynamic,
_ => unreachable!(),
};
let offset = in_section.sh_offset(endian) as usize + extra_offset;
let offset = round_up_to_alignment(offset, 8);
*out_offset = offset;
writer.reserve_until(offset);
let reserved_before = writer.reserved_len();
match i {
0 => {
writer.reserve_hash(3, hash_chain_count);
}
1 => {
addresses.gnu_hash = in_section.sh_addr(endian);
writer.reserve_gnu_hash(1, 1, gnu_hash_symbol_count);
}
2 => {
addresses.dynsym = in_section.sh_addr(endian);
writer.reserve_dynsym();
}
3 => {
addresses.dynstr = in_section.sh_addr(endian);
writer.reserve_dynstr();
}
4 => {
addresses.dynamic = in_section.sh_addr(endian);
writer.reserve_dynamic(dynamic_count);
}
_ => unreachable!(),
}
let reserved_after = writer.reserved_len();
extra_offset += {
let actual_size = reserved_after - reserved_before;
actual_size.saturating_sub(in_section.sh_size(endian) as usize)
};
}
(offsets, addresses)
}
}
use object::{elf, Endianness};
pub const fn round_up_to_alignment(width: usize, alignment: usize) -> usize {
match alignment {
@ -132,268 +14,110 @@ pub const fn round_up_to_alignment(width: usize, alignment: usize) -> usize {
}
}
pub fn create_dylib_elf64(
in_data: &[u8],
custom_names: &[String],
) -> object::read::Result<Vec<u8>> {
let in_elf: &elf::FileHeader64<Endianness> = elf::FileHeader64::parse(in_data)?;
let endian = in_elf.endian()?;
let in_segments = in_elf.program_headers(endian, in_data)?;
let in_sections = in_elf.sections(endian, in_data)?;
let in_syms = in_sections.symbols(endian, in_data, elf::SHT_SYMTAB)?;
let in_dynsyms = in_sections.symbols(endian, in_data, elf::SHT_DYNSYM)?;
let get_section = |name: &[u8]| {
*in_sections
.section_by_name(Endianness::Little, name)
.unwrap()
.1
};
let sections = Sections {
hash: get_section(b".hash" as &[_]),
gnu_hash: get_section(b".gnu.hash" as &[_]),
dynsym: get_section(b".dynsym" as &[_]),
dynstr: get_section(b".dynstr" as &[_]),
dynamic: get_section(b".dynamic" as &[_]),
};
pub fn create_dylib_elf64(custom_names: &[String]) -> object::read::Result<Vec<u8>> {
let endian = Endianness::Little;
let mut out_data = Vec::new();
let mut writer = object::write::elf::Writer::new(endian, in_elf.is_class_64(), &mut out_data);
let mut writer = object::write::elf::Writer::new(endian, true, &mut out_data);
const DYNAMIC_SECTION: usize = 2;
let out_sections_index = [
writer.reserve_hash_section_index(),
writer.reserve_gnu_hash_section_index(),
writer.reserve_dynsym_section_index(),
writer.reserve_dynstr_section_index(),
writer.reserve_dynamic_section_index(),
writer.reserve_symtab_section_index(),
writer.reserve_strtab_section_index(),
writer.reserve_shstrtab_section_index(),
];
// Assign dynamic strings.
//
// Dynamic section at offset 0x2268 contains 8 entries:
// Tag Type Name/Value
// 0x000000000000000e (SONAME) Library soname: [libapp.so]
// 0x0000000000000004 (HASH) 0x120
// 0x000000006ffffef5 (GNU_HASH) 0x130
// 0x0000000000000005 (STRTAB) 0x168
// 0x0000000000000006 (SYMTAB) 0x150
// 0x000000000000000a (STRSZ) 11 (bytes)
// 0x000000000000000b (SYMENT) 24 (bytes)
// 0x0000000000000000 (NULL) 0x0
let dynamic = |tag, val, string| Dynamic { tag, val, string };
let soname = writer.add_dynamic_string(b"libapp.so");
let out_dynamic = [
dynamic(elf::DT_SONAME, 1, Some(soname)),
dynamic(elf::DT_HASH, 288, None),
dynamic(elf::DT_GNU_HASH, 304, None),
dynamic(elf::DT_STRTAB, 360, None),
dynamic(elf::DT_SYMTAB, 336, None),
dynamic(elf::DT_STRSZ, 11, None),
dynamic(elf::DT_SYMENT, 24, None),
dynamic(elf::DT_NULL, 0, None),
];
let out_dynamic = [(elf::DT_SONAME, 1, Some(soname)), (elf::DT_NULL, 0, None)];
// Assign dynamic symbol indices.
let mut out_dynsyms = Vec::with_capacity(in_dynsyms.len());
for (j, name) in custom_names.iter().enumerate() {
let i = in_dynsyms.len().saturating_sub(1) + j;
let in_name = name.as_bytes();
let name = Some(writer.add_dynamic_string(in_name));
let gnu_hash = Some(elf::gnu_hash(in_name));
// .dynamic
let section = Some(out_sections_index[DYMAMIC_SECTION]);
out_dynsyms.push(DynamicSymbol {
in_sym: i,
name,
section,
gnu_hash,
let out_dynsyms: Vec<_> = custom_names
.iter()
.map(|name| {
(
writer.reserve_dynamic_symbol_index(),
writer.add_dynamic_string(name.as_bytes()),
)
})
}
.collect();
let mut out_dynsyms_index = vec![Default::default(); in_dynsyms.len() + custom_names.len()];
for out_dynsym in out_dynsyms.iter_mut() {
out_dynsyms_index[out_dynsym.in_sym] = writer.reserve_dynamic_symbol_index();
}
let dynamic_count = out_dynamic.len();
// Hash parameters.
let hash_chain_count = writer.dynamic_symbol_count();
// GNU hash parameters.
let gnu_hash_index_base = 0;
let gnu_hash_symbol_base = 1;
let gnu_hash_symbol_count = writer.dynamic_symbol_count() - gnu_hash_symbol_base;
// content of the symbol table
//
// Symbol table '.symtab' contains 8 entries:
// Num: Value Size Type Bind Vis Ndx Name
// 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
// 1: 0000000000000120 0 SECTION LOCAL DEFAULT UND
// 2: 0000000000000130 0 SECTION LOCAL DEFAULT 1
// 3: 0000000000000150 0 SECTION LOCAL DEFAULT 2
// 4: 0000000000000168 0 SECTION LOCAL DEFAULT 3
// 5: 0000000000001000 0 SECTION LOCAL DEFAULT 4
// 6: 0000000000001f30 0 SECTION LOCAL DEFAULT 5
// 7: 0000000000001f30 0 OBJECT LOCAL DEFAULT 5 _DYNAMIC
let symbol = |index, name| Symbol {
in_sym: index,
name,
};
let out_syms = [
symbol(1, None),
symbol(2, None),
symbol(3, None),
symbol(4, None),
symbol(5, None),
symbol(6, None),
symbol(7, Some(writer.add_string(b"_DYNAMIC"))),
];
// include the NULL symbol
let num_local = 1 + out_syms.len();
let mut out_syms_index = Vec::with_capacity(in_syms.len());
out_syms_index.push(Default::default());
for sym in out_syms.iter() {
out_syms_index.push(writer.reserve_symbol_index(Some(out_sections_index[sym.in_sym])));
}
// Start reserving file ranges.
writer.reserve_file_header();
// We don't support moving program headers.
assert_eq!(in_elf.e_phoff(endian), writer.reserved_len() as u64);
writer.reserve_program_headers(in_segments.len() as u32);
let dynsym_address = writer.reserved_len();
writer.reserve_dynsym();
let (offsets, addresses) = sections.reserve_alloc_sections(
&mut writer,
hash_chain_count,
gnu_hash_symbol_count,
out_dynamic.len(),
);
let dynstr_address = writer.reserved_len();
writer.reserve_dynstr();
let dynamic_address = round_up_to_alignment(writer.reserved_len(), 8);
writer.reserve_dynamic(dynamic_count);
writer.reserve_symtab();
writer.reserve_symtab_shndx();
writer.reserve_strtab();
writer.reserve_shstrtab();
writer.reserve_section_headers();
// writing
writer
.write_file_header(&object::write::elf::FileHeader {
os_abi: in_elf.e_ident().os_abi,
abi_version: in_elf.e_ident().abi_version,
e_type: in_elf.e_type(endian),
e_machine: in_elf.e_machine(endian),
e_entry: in_elf.e_entry(endian),
e_flags: in_elf.e_flags(endian),
os_abi: 0,
abi_version: 0,
e_type: 3,
e_machine: 62,
e_entry: 0x1000,
e_flags: 0,
})
.unwrap();
writer.write_align_program_headers();
for in_segment in in_segments {
writer.write_program_header(&object::write::elf::ProgramHeader {
p_type: in_segment.p_type(endian),
p_flags: in_segment.p_flags(endian),
// dirty hack really. Not sure if this is correct on its own
p_offset: if in_segment.p_offset(endian) > 0 {
offsets[DYMAMIC_SECTION] as _
} else {
0
},
p_vaddr: in_segment.p_vaddr(endian),
p_paddr: in_segment.p_paddr(endian),
p_filesz: in_segment.p_filesz(endian),
p_memsz: in_segment.p_memsz(endian),
p_align: in_segment.p_align(endian),
});
}
for (i, offset) in offsets.iter().enumerate() {
writer.pad_until(*offset);
match i {
0 => {
writer.write_hash(1, hash_chain_count, |_| None);
}
1 => {
writer.write_gnu_hash(1, 0, 1, 1, gnu_hash_symbol_count, |index| {
out_dynsyms[gnu_hash_index_base + index as usize]
.gnu_hash
.unwrap()
});
}
2 => {
writer.write_null_dynamic_symbol();
for sym in &out_dynsyms {
writer.write_dynamic_symbol(&object::write::elf::Sym {
name: sym.name,
section: sym.section,
st_info: (elf::STB_GLOBAL << 4) | elf::STT_FUNC,
st_other: 0,
st_shndx: 0,
st_value: 0x1000,
st_size: 0,
});
}
}
3 => {
writer.write_dynstr();
}
4 => {
for d in &out_dynamic {
if let Some(string) = d.string {
writer.write_dynamic_string(d.tag, string);
} else {
writer.write_dynamic(d.tag, d.val);
}
}
}
_ => unreachable!(),
// dynsym content
{
writer.write_null_dynamic_symbol();
for (_index, name) in out_dynsyms {
writer.write_dynamic_symbol(&object::write::elf::Sym {
name: Some(name),
section: Some(out_sections_index[DYNAMIC_SECTION]),
st_info: (elf::STB_GLOBAL << 4) | elf::STT_FUNC,
st_other: 0,
st_shndx: 0,
st_value: 0x1000,
st_size: 0,
});
}
}
writer.write_null_symbol();
let section_indices = [0, 1, 2, 3, 4, 5, 5];
for (sym, sindex) in out_syms.iter().zip(section_indices) {
let in_sym = in_syms.symbol(sym.in_sym)?;
writer.write_symbol(&object::write::elf::Sym {
name: sym.name,
section: Some(object::write::elf::SectionIndex(sindex)),
st_info: in_sym.st_info(),
st_other: in_sym.st_other(),
st_shndx: in_sym.st_shndx(endian),
st_value: in_sym.st_value(endian),
st_size: in_sym.st_size(endian),
});
// dynstr content
writer.write_dynstr();
// dynamic content
writer.write_align_dynamic();
for (tag, val, opt_string) in out_dynamic {
if let Some(string) = opt_string {
writer.write_dynamic_string(tag, string);
} else {
writer.write_dynamic(tag, val);
}
}
writer.write_symtab_shndx();
// strtab content
writer.write_strtab();
writer.write_shstrtab();
// SECTION HEADERS
writer.write_null_section_header();
writer.write_hash_section_header(addresses.hash);
writer.write_gnu_hash_section_header(addresses.gnu_hash);
writer.write_dynsym_section_header(addresses.dynsym, 1);
writer.write_dynsym_section_header(dynsym_address as _, 1);
writer.write_dynstr_section_header(addresses.dynstr);
writer.write_dynstr_section_header(dynstr_address as _);
writer.write_dynamic_section_header(addresses.dynamic);
writer.write_symtab_section_header(num_local as _);
writer.write_dynamic_section_header(dynamic_address as _);
writer.write_strtab_section_header();
writer.write_shstrtab_section_header();

5
crates/linker/src/generate_dylib/mod.rs
View file

@ -3,12 +3,9 @@ use target_lexicon::Triple;
mod elf64;
mod pe;
/// an empty shared library, that we build on top of
const DUMMY_ELF64: &[u8] = include_bytes!("../../dummy-elf64-x86-64.so");
pub fn generate(target: &Triple, custom_names: &[String]) -> object::read::Result<Vec<u8>> {
match target.binary_format {
target_lexicon::BinaryFormat::Elf => elf64::create_dylib_elf64(DUMMY_ELF64, custom_names),
target_lexicon::BinaryFormat::Elf => elf64::create_dylib_elf64(custom_names),
target_lexicon::BinaryFormat::Macho => todo!("macho dylib creation"),
target_lexicon::BinaryFormat::Coff => Ok(pe::synthetic_dll(custom_names)),
other => unimplemented!("dylib creation for {:?}", other),