Elf.h
#ifndef HALIDE_ELF_H
#define HALIDE_ELF_H
#include <algorithm>
#include <iterator>
#include <limits>
#include <list>
#include <memory>
#include <string>
#include <utility>
#include <vector>
namespace Halide {
namespace Internal {
namespace Elf {
// This ELF parser mostly deserializes the object into a graph
// structure in memory. It replaces indices into tables (sections,
// symbols, etc.) with a weakly referenced graph of pointers. The
// Object datastructure owns all of the objects. This namespace exists
// because it is very difficult to use LLVM's object parser to modify
// an object (it's fine for parsing only). This was built using
// http://www.skyfree.org/linux/references/ELF_Format.pdf as a reference
// for the ELF structs and constants.
class Object;
class Symbol;
class Section;
class Relocation;
// Helpful wrapper to allow range-based for loops.
template <typename T>
class iterator_range {
T b, e;
public:
iterator_range(T b, T e) : b(b), e(e) {}
T begin() const { return b; }
T end() const { return e; }
};
/** Describes a symbol */
class Symbol {
public:
enum Binding : uint8_t {
STB_LOCAL = 0,
STB_GLOBAL = 1,
STB_WEAK = 2,
STB_LOPROC = 13,
STB_HIPROC = 15,
};
enum Type : uint8_t {
STT_NOTYPE = 0,
STT_OBJECT = 1,
STT_FUNC = 2,
STT_SECTION = 3,
STT_FILE = 4,
STT_LOPROC = 13,
STT_HIPROC = 15,
};
enum Visibility : uint8_t {
STV_DEFAULT = 0,
STV_INTERNAL = 1,
STV_HIDDEN = 2,
STV_PROTECTED = 3,
};
private:
std::string name;
const Section *definition = nullptr;
uint64_t offset = 0;
uint32_t size = 0;
Binding binding = STB_LOCAL;
Type type = STT_NOTYPE;
Visibility visibility = STV_DEFAULT;
public:
Symbol() {}
Symbol(const std::string &name) : name(name) {}
/** Accesses the name of this symbol. */
///@{
Symbol &set_name(const std::string &name) {
this->name = name;
return *this;
}
const std::string &get_name() const { return name; }
///@}
/** Accesses the type of this symbol. */
///@{
Symbol &set_type(Type type) {
this->type = type;
return *this;
}
Type get_type() const { return type; }
///@}
/** Accesses the properties that describe the definition of this symbol. */
///@{
Symbol &define(const Section *section, uint64_t offset, uint32_t size) {
this->definition = section;
this->offset = offset;
this->size = size;
return *this;
}
bool is_defined() const { return definition != nullptr; }
const Section *get_section() const { return definition; }
uint64_t get_offset() const { return offset; }
uint32_t get_size() const { return size; }
///@}
/** Access the binding and visibility of this symbol. See the ELF
* spec for more information about these properties. */
///@{
Symbol &set_binding(Binding binding) {
this->binding = binding;
return *this;
}
Symbol &set_visibility(Visibility visibility) {
this->visibility = visibility;
return *this;
}
Binding get_binding() const { return binding; }
Visibility get_visibility() const { return visibility; }
///@}
};
/** Describes a relocation to be applied to an offset of a section in
* an Object. */
class Relocation {
uint32_t type = 0;
uint64_t offset = 0;
int64_t addend = 0;
const Symbol *symbol = nullptr;
public:
Relocation() {}
Relocation(uint32_t type, uint64_t offset, int64_t addend, const Symbol *symbol)
: type(type), offset(offset), addend(addend), symbol(symbol) {}
/** The type of relocation to be applied. The meaning of this
* value depends on the machine of the object. */
///@{
Relocation &set_type(uint32_t type) {
this->type = type;
return *this;
}
uint32_t get_type() const { return type; }
///@}
/** Where to apply the relocation. This is relative to the section
* the relocation belongs to. */
///@{
Relocation &set_offset(uint64_t offset) {
this->offset = offset;
return *this;
}
uint64_t get_offset() const { return offset; }
///@}
/** The value to replace with the relocation is the address of the symbol plus the addend. */
///@{
Relocation &set_symbol(const Symbol *symbol) {
this->symbol = symbol;
return *this;
}
Relocation &set_addend(int64_t addend) {
this->addend = addend;
return *this;
}
const Symbol *get_symbol() const { return symbol; }
int64_t get_addend() const { return addend; }
///@}
};
/** Describes a section of an object file. */
class Section {
public:
enum Type : uint32_t {
SHT_NULL = 0,
SHT_PROGBITS = 1,
SHT_SYMTAB = 2,
SHT_STRTAB = 3,
SHT_RELA = 4,
SHT_HASH = 5,
SHT_DYNAMIC = 6,
SHT_NOTE = 7,
SHT_NOBITS = 8,
SHT_REL = 9,
SHT_SHLIB = 10,
SHT_DYNSYM = 11,
SHT_LOPROC = 0x70000000,
SHT_HIPROC = 0x7fffffff,
SHT_LOUSER = 0x80000000,
SHT_HIUSER = 0xffffffff,
};
enum Flag : uint32_t {
SHF_WRITE = 0x1,
SHF_ALLOC = 0x2,
SHF_EXECINSTR = 0x4,
SHF_MASKPROC = 0xf0000000,
};
typedef std::vector<Relocation> RelocationList;
typedef RelocationList::iterator relocation_iterator;
typedef RelocationList::const_iterator const_relocation_iterator;
typedef std::vector<char>::iterator contents_iterator;
typedef std::vector<char>::const_iterator const_contents_iterator;
private:
std::string name;
Type type = SHT_NULL;
uint32_t flags = 0;
std::vector<char> contents;
// Sections may have a size larger than the contents.
uint64_t size = 0;
uint64_t alignment = 1;
RelocationList relocs;
public:
Section() {}
Section(const std::string &name, Type type) : name(name), type(type) {}
Section &set_name(const std::string &name) {
this->name = name;
return *this;
}
const std::string &get_name() const { return name; }
Section &set_type(Type type) {
this->type = type;
return *this;
}
Type get_type() const { return type; }
Section &set_flag(Flag flag) {
this->flags |= flag;
return *this; }
Section &remove_flag(Flag flag) {
this->flags &= ~flag;
return *this;
}
Section &set_flags(uint32_t flags) {
this->flags = flags;
return *this;
}
uint32_t get_flags() const { return flags; }
bool is_alloc() const { return (flags & SHF_ALLOC) != 0; }
bool is_writable() const { return (flags & SHF_WRITE) != 0; }
/** Get or set the size of the section. The size may be larger
* than the content. */
///@{
Section &set_size(uint64_t size) {
this->size = size;
return *this;
}
uint64_t get_size() const { return std::max((uint64_t) size, (uint64_t) contents.size()); }
///@}
Section &set_alignment(uint64_t alignment) {
this->alignment = alignment;
return *this;
}
uint64_t get_alignment() const { return alignment; }
Section &set_contents(std::vector<char> contents) {
this->contents = std::move(contents);
return *this;
}
template <typename It>
Section &set_contents(It begin, It end) {
this->contents.assign(begin, end);
return *this;
}
template <typename It>
Section &append_contents(It begin, It end) {
this->contents.insert(this->contents.end(), begin, end);
return *this;
}
template <typename It>
Section &prepend_contents(It begin, It end) {
typedef typename std::iterator_traits<It>::value_type T;
uint64_t size_bytes = std::distance(begin, end) * sizeof(T);
this->contents.insert(this->contents.begin(), begin, end);
// When we add data to the start of the section, we need to fix up
// the offsets of the relocations linked to this section.
for (Relocation &r : relocations()) {
r.set_offset(r.get_offset() + size_bytes);
}
return *this;
}
/** Set, append or prepend an object to the contents, assuming T is a
* trivially copyable datatype. */
template <typename T>
Section &set_contents(const std::vector<T> &contents) {
this->contents.assign((const char *)contents.data(), (const char *)(contents.data() + contents.size()));
return *this;
}
template <typename T>
Section &append_contents(const T& x) {
return append_contents((const char *)&x, (const char *)(&x + 1));
}
template <typename T>
Section &prepend_contents(const T& x) {
return prepend_contents((const char *)&x, (const char *)(&x + 1));
}
const std::vector<char> &get_contents() const { return contents; }
contents_iterator contents_begin() { return contents.begin(); }
contents_iterator contents_end() { return contents.end(); }
const_contents_iterator contents_begin() const { return contents.begin(); }
const_contents_iterator contents_end() const { return contents.end(); }
const char *contents_data() const { return contents.data(); }
size_t contents_size() const { return contents.size(); }
bool contents_empty() const { return contents.empty(); }
Section &set_relocations(std::vector<Relocation> relocs) {
this->relocs = std::move(relocs);
return *this;
}
template <typename It>
Section &set_relocations(It begin, It end) {
this->relocs.assign(begin, end);
return *this;
}
void add_relocation(const Relocation &reloc) { relocs.push_back(reloc); }
relocation_iterator relocations_begin() { return relocs.begin(); }
relocation_iterator relocations_end() { return relocs.end(); }
iterator_range<relocation_iterator> relocations() { return {relocs.begin(), relocs.end()}; }
const_relocation_iterator relocations_begin() const { return relocs.begin(); }
const_relocation_iterator relocations_end() const { return relocs.end(); }
iterator_range<const_relocation_iterator> relocations() const { return {relocs.begin(), relocs.end()}; }
size_t relocations_size() const { return relocs.size(); }
};
/** Base class for a target architecture to implement the target
* specific aspects of linking. */
class Linker {
public:
virtual ~Linker() {}
virtual uint16_t get_machine() = 0;
virtual uint32_t get_flags() = 0;
virtual uint32_t get_version() = 0;
virtual void append_dynamic(Section &dynamic) = 0;
/** Add or get an entry to the global offset table (GOT) with a
* relocation pointing to sym. */
virtual uint64_t get_got_entry(Section &got, const Symbol &sym) = 0;
/** Check to see if this relocation should go through the PLT. */
virtual bool needs_plt_entry(const Relocation &reloc) = 0;
/** Add a PLT entry for a symbol sym defined externally. Returns a
* symbol representing the PLT entry. */
virtual Symbol add_plt_entry(const Symbol &sym, Section &plt, Section &got,
const Symbol &got_sym) = 0;
/** Perform a relocation. This function may opt to not apply the
* relocation, and return a new relocation to be performed at
* runtime. This requires that the section to apply the relocation
* to is writable at runtime. */
virtual Relocation relocate(uint64_t fixup_offset, char *fixup_addr, uint64_t type,
const Symbol *sym, uint64_t sym_offset, int64_t addend,
Section &got) = 0;
};
/** Holds all of the relevant sections and symbols for an object. */
class Object {
public:
enum Type : uint16_t {
ET_NONE = 0,
ET_REL = 1,
ET_EXEC = 2,
ET_DYN = 3,
ET_CORE = 4,
ET_LOPROC = 0xff00,
ET_HIPROC = 0xffff,
};
// We use lists for sections and symbols to avoid iterator
// invalidation when we modify the containers.
typedef std::list<Section> SectionList;
typedef typename SectionList::iterator section_iterator;
typedef typename SectionList::const_iterator const_section_iterator;
typedef std::list<Symbol> SymbolList;
typedef typename SymbolList::iterator symbol_iterator;
typedef typename SymbolList::const_iterator const_symbol_iterator;
private:
SectionList secs;
SymbolList syms;
Type type = ET_NONE;
uint16_t machine = 0;
uint32_t version = 0;
uint64_t entry = 0;
uint32_t flags = 0;
Object(const Object &);
void operator = (const Object &);
public:
Object() {}
Type get_type() const { return type; }
uint16_t get_machine() const { return machine; }
uint32_t get_version() const { return version; }
uint64_t get_entry() const { return entry; }
uint32_t get_flags() const { return flags; }
Object &set_type(Type type) {
this->type = type;
return *this;
}
Object &set_machine(uint16_t machine) {
this->machine = machine;
return *this;
}
Object &set_version(uint32_t version) {
this->version = version;
return *this;
}
Object &set_entry(uint64_t entry) {
this->entry = entry;
return *this;
}
Object &set_flags(uint32_t flags) {
this->flags = flags;
return *this;
}
/** Parse an object in memory to an Object. */
static std::unique_ptr<Object> parse_object(const char *data, size_t size);
/** Write a shared object in memory. */
std::vector<char> write_shared_object(Linker *linker, const std::vector<std::string> &depedencies = {},
const std::string &soname = "");
section_iterator sections_begin() { return secs.begin(); }
section_iterator sections_end() { return secs.end(); }
iterator_range<section_iterator> sections() { return {secs.begin(), secs.end()}; }
const_section_iterator sections_begin() const { return secs.begin(); }
const_section_iterator sections_end() const { return secs.end(); }
iterator_range<const_section_iterator> sections() const { return {secs.begin(), secs.end()}; }
size_t sections_size() const { return secs.size(); }
section_iterator find_section(const std::string &name);
section_iterator add_section(const std::string &name, Section::Type type);
section_iterator add_relocation_section(const Section &for_section);
section_iterator erase_section(section_iterator i) { return secs.erase(i); }
section_iterator merge_sections(const std::vector<section_iterator> §ions);
section_iterator merge_text_sections();
symbol_iterator symbols_begin() { return syms.begin(); }
symbol_iterator symbols_end() { return syms.end(); }
iterator_range<symbol_iterator> symbols() { return {syms.begin(), syms.end()}; }
const_symbol_iterator symbols_begin() const { return syms.begin(); }
const_symbol_iterator symbols_end() const { return syms.end(); }
iterator_range<const_symbol_iterator> symbols() const { return {syms.begin(), syms.end()}; }
size_t symbols_size() const { return syms.size(); }
symbol_iterator find_symbol(const std::string &name);
const_symbol_iterator find_symbol(const std::string &name) const;
symbol_iterator add_symbol(const std::string &name);
};
} // namespace Elf
} // namespace Internal
} // namespace Halide
#endif