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elf.cc
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elf.cc
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/*
* Copyright (C) 2013 Cloudius Systems, Ltd.
*
* This work is open source software, licensed under the terms of the
* BSD license as described in the LICENSE file in the top-level directory.
*/
#include <osv/elf.hh>
#include <osv/app.hh>
#include <osv/mmu.hh>
#include <boost/format.hpp>
#include <exception>
#include <memory>
#include <string.h>
#include <osv/align.hh>
#include <osv/debug.hh>
#include <stdlib.h>
#include <unistd.h>
#include <boost/algorithm/string.hpp>
#include <boost/range/algorithm/find.hpp>
#include <functional>
#include <iterator>
#include <osv/sched.hh>
#include <osv/trace.hh>
#include <osv/version.hh>
#include <osv/stubbing.hh>
#include <sys/utsname.h>
#include <osv/demangle.hh>
#include <boost/version.hpp>
#include <deque>
#include "arch.hh"
#define ELF_DEBUG_ENABLED 0
#if ELF_DEBUG_ENABLED
#define elf_debug(format,...) kprintf("ELF [tid:%d, %s]: " format, sched::thread::current()->id(), _pathname.c_str(), ##__VA_ARGS__)
#else
#define elf_debug(...)
#endif
TRACEPOINT(trace_elf_load, "%s", const char *);
TRACEPOINT(trace_elf_unload, "%s", const char *);
TRACEPOINT(trace_elf_lookup, "%s", const char *);
TRACEPOINT(trace_elf_lookup_next, "%s", const char *);
TRACEPOINT(trace_elf_lookup_addr, "%p", const void *);
extern void* elf_start;
extern size_t elf_size;
using namespace boost::range;
namespace {
typedef boost::format fmt;
}
namespace elf {
const ulong program::core_module_index = 0;
namespace {
unsigned symbol_type(Elf64_Sym& sym)
{
return sym.st_info & 15;
}
unsigned symbol_binding(Elf64_Sym& sym)
{
return sym.st_info >> 4;
}
}
symbol_module::symbol_module()
: symbol()
, obj()
{
}
symbol_module::symbol_module(Elf64_Sym* _sym, object* _obj)
: symbol(_sym)
, obj(_obj)
{
}
void* symbol_module::relocated_addr() const
{
void* base = obj->base();
if (symbol->st_shndx == SHN_UNDEF || symbol->st_shndx == SHN_ABS) {
base = 0;
}
switch (symbol_type(*symbol)) {
case STT_NOTYPE:
return reinterpret_cast<void*>(symbol->st_value);
break;
case STT_OBJECT:
case STT_FUNC:
return base + symbol->st_value;
break;
case STT_IFUNC:
return reinterpret_cast<void *(*)()>(base + symbol->st_value)();
default:
abort("Unknown symbol type %d\n", symbol_type(*symbol));
}
}
u64 symbol_module::size() const
{
return symbol->st_size;
}
std::atomic<ptrdiff_t> object::_static_tls_alloc;
object::object(program& prog, std::string pathname)
: _prog(prog)
, _pathname(pathname)
, _tls_segment()
, _tls_init_size()
, _tls_uninit_size()
, _static_tls(false)
, _static_tls_offset(0)
, _initial_tls_size(0)
, _dynamic_table(nullptr)
, _module_index(_prog.register_dtv(this))
, _is_executable(false)
, _visibility_thread(nullptr)
, _visibility_level(VisibilityLevel::Public)
{
elf_debug("Instantiated\n");
}
object::~object()
{
elf_debug("Removed\n");
_prog.free_dtv(this);
}
ulong object::module_index() const
{
return _module_index;
}
bool object::visible(void) const
{
auto level = _visibility_level.load(std::memory_order_acquire);
if (level == VisibilityLevel::Public) {
return true;
}
auto thread = _visibility_thread.load(std::memory_order_acquire);
if (!thread) { //Unlikely, but ...
return true;
}
auto current_thread = sched::thread::current();
if (level == VisibilityLevel::ThreadOnly) {
return thread == current_thread;
}
// Is current thread the same as "thread" or is it a child of it?
if (thread == current_thread) {
return true;
}
bool visible = false;
auto next_parent_id = current_thread->parent_id();
while (next_parent_id) {
sched::with_thread_by_id(next_parent_id, [&next_parent_id, &visible, thread] (sched::thread *t) {
if (t == thread) {
visible = true;
next_parent_id = 0;
} else {
next_parent_id = t ? t->parent_id() : 0;
}
});
}
return visible;
}
void object::set_visibility(elf::VisibilityLevel visibilityLevel)
{
_visibility_thread.store(visibilityLevel == VisibilityLevel::Public ? nullptr : sched::thread::current(),
std::memory_order_release);
_visibility_level.store(visibilityLevel, std::memory_order_release);
}
template <>
void* object::lookup(const char* symbol)
{
symbol_module sm{lookup_symbol(symbol, false), this};
if (!sm.symbol || sm.symbol->st_shndx == SHN_UNDEF) {
return nullptr;
}
return sm.relocated_addr();
}
void* object::cached_lookup(const std::string& name)
{
auto cached_address_it = _cached_symbols.find(name);
if (cached_address_it != _cached_symbols.end()) {
return cached_address_it->second;
}
else {
void *symbol_address = lookup(name.c_str());
_cached_symbols[name] = symbol_address;
return symbol_address;
}
}
std::vector<Elf64_Shdr> object::sections()
{
size_t bytes = size_t(_ehdr.e_shentsize) * _ehdr.e_shnum;
std::unique_ptr<char[]> tmp(new char[bytes]);
read(_ehdr.e_shoff, tmp.get(), bytes);
auto p = tmp.get();
std::vector<Elf64_Shdr> ret;
for (unsigned i = 0; i < _ehdr.e_shnum; ++i, p += _ehdr.e_shentsize) {
ret.push_back(*reinterpret_cast<Elf64_Shdr*>(p));
}
return ret;
}
std::string object::section_name(const Elf64_Shdr& shdr)
{
if (_ehdr.e_shstrndx == SHN_UNDEF) {
return {};
}
if (!_section_names_cache) {
auto s = sections().at(_ehdr.e_shstrndx);
std::unique_ptr<char[]> p(new char[s.sh_size]);
read(s.sh_offset, p.get(), s.sh_size);
_section_names_cache = std::move(p);
}
return _section_names_cache.get() + shdr.sh_name;
}
std::vector<Elf64_Sym> object::symbols() {
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
auto len = symtab_len();
return std::vector<Elf64_Sym>(symtab, symtab + len);
}
const char * object::symbol_name(const Elf64_Sym * sym) {
auto strtab = dynamic_ptr<char>(DT_STRTAB);
return strtab + sym->st_name;
}
void* object::entry_point() const {
if (!_is_executable) {
return nullptr;
}
return _base + _ehdr.e_entry;
}
file::file(program& prog, ::fileref f, std::string pathname)
: object(prog, pathname)
, _f(f)
{
load_elf_header();
load_program_headers();
}
file::~file()
{
}
memory_image::memory_image(program& prog, void* base)
: object(prog, "")
{
_ehdr = *static_cast<Elf64_Ehdr*>(base);
auto p = static_cast<Elf64_Phdr*>(base + _ehdr.e_phoff);
assert(_ehdr.e_phentsize == sizeof(*p));
_phdrs.assign(p, p + _ehdr.e_phnum);
}
void memory_image::load_segment(const Elf64_Phdr& phdr)
{
}
void memory_image::unload_segment(const Elf64_Phdr& phdr)
{
}
void memory_image::read(Elf64_Off offset, void* data, size_t size)
{
throw std::runtime_error("cannot load from Elf memory image");
}
void file::load_elf_header()
{
try {
read(0, &_ehdr, sizeof(_ehdr));
} catch(error &e) {
throw osv::invalid_elf_error(
std::string("can't read elf header: ") + strerror(e.get()));
}
if (!(_ehdr.e_ident[EI_MAG0] == '\x7f'
&& _ehdr.e_ident[EI_MAG1] == 'E'
&& _ehdr.e_ident[EI_MAG2] == 'L'
&& _ehdr.e_ident[EI_MAG3] == 'F')) {
throw osv::invalid_elf_error("bad elf header");
}
if (!(_ehdr.e_ident[EI_CLASS] == ELFCLASS64)) {
throw osv::invalid_elf_error("bad elf class");
}
if (!(_ehdr.e_ident[EI_DATA] == ELFDATA2LSB)) {
throw osv::invalid_elf_error("bad elf endianness");
}
if (!(_ehdr.e_ident[EI_VERSION] == EV_CURRENT)) {
throw osv::invalid_elf_error("bad elf version");
}
if (!(_ehdr.e_ident[EI_OSABI] == ELFOSABI_LINUX
|| _ehdr.e_ident[EI_OSABI] == 0)) {
throw osv::invalid_elf_error("bad os abi");
}
if (!(_ehdr.e_type == ET_DYN || _ehdr.e_type == ET_EXEC)) {
throw osv::invalid_elf_error(
"bad executable type (only shared-object, PIE or non-PIE executable supported)");
}
}
void file::read(Elf64_Off offset, void* data, size_t size)
{
// read(fileref, ...) is void, and crashes with assertion failure if the
// file is not long enough. So we need to check first.
if (::size(_f) < offset + size) {
throw osv::invalid_elf_error("executable too short");
}
::read(_f, data, offset, size);
}
namespace {
void* align(void* addr, ulong align, ulong offset)
{
return align_up(addr - offset, align) + offset;
}
}
static bool intersects_with_kernel(Elf64_Addr elf_addr)
{
void *addr = reinterpret_cast<void*>(elf_addr);
return addr >= elf_start && addr < elf_start + elf_size;
}
void object::set_base(void* base)
{
auto p = std::min_element(_phdrs.begin(), _phdrs.end(),
[](Elf64_Phdr a, Elf64_Phdr b)
{ return a.p_type == PT_LOAD
&& a.p_vaddr < b.p_vaddr; });
auto q = std::min_element(_phdrs.begin(), _phdrs.end(),
[](Elf64_Phdr a, Elf64_Phdr b)
{ return a.p_type == PT_LOAD
&& a.p_vaddr > b.p_vaddr; });
if (!is_core() && is_non_pie_executable()) {
// Verify non-PIE executable does not collide with the kernel
if (intersects_with_kernel(p->p_vaddr) || intersects_with_kernel(q->p_vaddr + q->p_memsz)) {
abort("Non-PIE executable [%s] collides with kernel: [%p-%p] !\n",
pathname().c_str(), p->p_vaddr, q->p_vaddr + q->p_memsz);
}
// Override the passed in value as the base for non-PIEs (Position Dependant Executables)
// needs to be set to 0 because all the addresses in it are absolute
_base = 0x0;
} else {
// Otherwise for kernel, PIEs and shared libraries set the base as requested by caller
_base = align(base, p->p_align, p->p_vaddr & (p->p_align - 1)) - p->p_vaddr;
}
_end = _base + q->p_vaddr + q->p_memsz;
elf_debug("The base set to: 0x%016x and end: 0x%016x\n", _base, _end);
}
void* object::base() const
{
return _base;
}
void* object::end() const
{
return _end;
}
void file::load_program_headers()
{
_phdrs.resize(_ehdr.e_phnum);
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
read(_ehdr.e_phoff + i * _ehdr.e_phentsize,
&_phdrs[i],
_ehdr.e_phentsize);
}
}
void file::load_segment(const Elf64_Phdr& phdr)
{
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong filesz_unaligned = phdr.p_vaddr + phdr.p_filesz - vstart;
ulong filesz = align_up(filesz_unaligned, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
unsigned perm = get_segment_mmap_permissions(phdr);
auto flag = mmu::mmap_fixed | (mlocked() ? mmu::mmap_populate : 0);
mmu::map_file(_base + vstart, filesz, flag, perm, _f, align_down(phdr.p_offset, mmu::page_size));
if (phdr.p_filesz != phdr.p_memsz) {
assert(perm & mmu::perm_write);
memset(_base + vstart + filesz_unaligned, 0, filesz - filesz_unaligned);
if (memsz != filesz) {
mmu::map_anon(_base + vstart + filesz, memsz - filesz, flag, perm);
}
}
elf_debug("Loaded and mapped PT_LOAD segment at: 0x%016x of size: 0x%x\n", _base + vstart, filesz); //TODO: Add memory?
}
bool object::mlocked()
{
for (auto&& s : sections()) {
if (section_name(s) == ".note.osv-mlock") {
return true;
}
}
return false;
}
bool object::has_non_writable_text_relocations()
{
return dynamic_exists(DT_TEXTREL);
}
Elf64_Note::Elf64_Note(void *_base, char *str)
{
Elf64_Word *base = reinterpret_cast<Elf64_Word *>(_base);
n_type = base[2];
n_owner.reserve(base[0]);
n_value.reserve(base[1]);
// The note section strings will include the trailing 0. std::string
// doesn't like that very much, and comparisons against a string that is
// constructed from this string will fail. Therefore the - 1 at the end
if (base[0] > 0) {
n_owner.assign(str, base[0] -1);
}
str = align_up(str + base[0], 4);
if (base[1] > 0) {
n_value.assign(str, base[1] - 1);
}
}
extern "C" char _pie_static_tls_start, _pie_static_tls_end;
void object::load_segments()
{
elf_debug("Loading segments\n");
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
auto &phdr = _phdrs[i];
if (phdr.p_type == PT_LOAD) {
load_segment(phdr);
}
}
}
void object::process_headers()
{
elf_debug("Processing headers\n");
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
auto &phdr = _phdrs[i];
switch (phdr.p_type) {
case PT_NULL:
break;
case PT_DYNAMIC:
_dynamic_table = reinterpret_cast<Elf64_Dyn*>(_base + phdr.p_vaddr);
break;
case PT_INTERP:
_is_executable = true;
break;
case PT_NOTE: {
if (phdr.p_memsz < 16) {
/* we have the PT_NOTE segment in the linker scripts,
* but if we have no note sections we will end up with
* a zero length segment. Handle this case by validating
* the phdr length.
*/
break;
}
void *start = _base + phdr.p_vaddr;
char *str = align_up((char *)start + 3 * sizeof(Elf64_Word), 4);
struct Elf64_Note header(start, str);
if (header.n_type != NT_VERSION) {
break;
}
if (header.n_owner != "OSv") {
break;
}
// FIXME: In the future, we should probably prevent loading of libosv.so in this
// situation.
if (header.n_value != osv::version()) {
printf("WARNING: libosv.so version mismatch. Kernel is %s, lib is %s\n",
osv::version().c_str(), header.n_value.c_str());
}
break;
}
case PT_LOAD:
case PT_PHDR:
case PT_GNU_STACK:
case PT_GNU_RELRO:
case PT_GNU_EH_FRAME:
case PT_PAX_FLAGS:
case PT_GNU_PROPERTY:
break;
case PT_TLS:
_tls_segment = _base + phdr.p_vaddr;
_tls_init_size = phdr.p_filesz;
_tls_uninit_size = phdr.p_memsz - phdr.p_filesz;
_tls_alignment = phdr.p_align;
elf_debug("Found TLS segment at 0x%016x of aligned size: %x\n", _tls_segment, get_aligned_tls_size());
break;
default:
abort("Unknown p_type in executable %s: %d\n", pathname(), phdr.p_type);
}
}
if (!is_core() && _ehdr.e_type == ET_EXEC && !_is_executable) {
abort("Statically linked executables are not supported!\n");
}
if (_is_executable && _tls_segment) {
auto app_tls_size = get_aligned_tls_size();
ulong pie_static_tls_maximum_size = &_pie_static_tls_end - &_pie_static_tls_start;
if (app_tls_size > pie_static_tls_maximum_size) {
// The reservation at the end of the kernel TLS is NOT big enough
// to hold the app static TLS. Let us calculate what the reservation should be
// and inform user how to relink kernel
auto kernel_tls_size = sched::kernel_tls_size();
auto kernel_tls_used_size = kernel_tls_size - pie_static_tls_maximum_size;
auto kernel_tls_needed_size = align_up(kernel_tls_used_size + app_tls_size, 64UL);
auto app_tls_needed_size = kernel_tls_needed_size - kernel_tls_used_size;
std::cout << "WARNING: " << pathname() << " is a PIE using TLS of size " << app_tls_size
<< " which is greater than the " << pie_static_tls_maximum_size << " bytes limit. "
<< "Either re-link the kernel by adding 'app_local_exec_tls_size=" << app_tls_needed_size
<< "' to ./scripts/build or re-link the app with '-shared' instead of '-pie'.\n";
}
}
}
void file::unload_segment(const Elf64_Phdr& phdr)
{
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong filesz_unaligned = phdr.p_vaddr + phdr.p_filesz - vstart;
ulong filesz = align_up(filesz_unaligned, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
mmu::munmap(_base + vstart, filesz);
mmu::munmap(_base + vstart + filesz, memsz - filesz);
}
void object::unload_segments()
{
for (unsigned i = 0; i < _ehdr.e_phnum; ++i) {
auto &phdr = _phdrs[i];
switch (phdr.p_type) {
case PT_LOAD:
unload_segment(phdr);
break;
default:
break;
}
}
}
unsigned object::get_segment_mmap_permissions(const Elf64_Phdr& phdr)
{
unsigned perm = 0;
if (phdr.p_flags & PF_X)
perm |= mmu::perm_exec;
if (phdr.p_flags & PF_W)
perm |= mmu::perm_write;
if (phdr.p_flags & PF_R)
perm |= mmu::perm_read;
return perm;
}
void object::fix_permissions()
{
if(has_non_writable_text_relocations()) {
make_text_writable(false);
}
for (auto&& phdr : _phdrs) {
if (phdr.p_type != PT_GNU_RELRO)
continue;
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
mmu::mprotect(_base + vstart, memsz, mmu::perm_read);
}
}
void object::make_text_writable(bool flag)
{
for (auto&& phdr : _phdrs) {
if (phdr.p_type != PT_LOAD)
continue;
ulong vstart = align_down(phdr.p_vaddr, mmu::page_size);
ulong memsz = align_up(phdr.p_vaddr + phdr.p_memsz, mmu::page_size) - vstart;
unsigned perm = get_segment_mmap_permissions(phdr);
mmu::mprotect(_base + vstart, memsz, flag ? perm | mmu::perm_write : perm);
}
}
template <typename T>
T* object::dynamic_ptr(unsigned tag)
{
return static_cast<T*>(_base + dynamic_tag(tag).d_un.d_ptr);
}
Elf64_Xword object::dynamic_val(unsigned tag)
{
return dynamic_tag(tag).d_un.d_val;
}
const char* object::dynamic_str(unsigned tag)
{
return dynamic_ptr<const char>(DT_STRTAB) + dynamic_val(tag);
}
bool object::dynamic_exists(unsigned tag)
{
return _dynamic_tag(tag);
}
Elf64_Dyn* object::_dynamic_tag(unsigned tag)
{
if (!_dynamic_table) {
return nullptr;
}
for (auto p = _dynamic_table; p->d_tag != DT_NULL; ++p) {
if (p->d_tag == tag) {
return p;
}
}
return nullptr;
}
Elf64_Dyn& object::dynamic_tag(unsigned tag)
{
auto r = _dynamic_tag(tag);
if (!r) {
throw osv::invalid_elf_error("missing tag");
}
return *r;
}
std::vector<const char *>
object::dynamic_str_array(unsigned tag)
{
auto strtab = dynamic_ptr<const char>(DT_STRTAB);
std::vector<const char *> r;
for (auto p = _dynamic_table; p->d_tag != DT_NULL; ++p) {
if (p->d_tag == tag) {
r.push_back(strtab + p->d_un.d_val);
}
}
return r;
}
static std::string demangle(const char *name) {
auto demangled = osv::demangle(name);
std::string ret(name);
if (demangled) {
ret += " (";
ret += demangled.get();
ret += ")";
}
return ret;
}
symbol_module object::symbol(unsigned idx, bool ignore_missing)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
assert(dynamic_val(DT_SYMENT) == sizeof(Elf64_Sym));
auto sym = &symtab[idx];
auto binding = symbol_binding(*sym);
if (binding == STB_LOCAL) {
return symbol_module(sym, this);
}
auto nameidx = sym->st_name;
auto name = dynamic_ptr<const char>(DT_STRTAB) + nameidx;
auto ret = _prog.lookup(name, this);
if (!ret.symbol && binding == STB_WEAK) {
return symbol_module(sym, this);
}
if (!ret.symbol) {
if (ignore_missing) {
debug("%s: ignoring missing symbol %s\n", pathname().c_str(), demangle(name).c_str());
} else {
abort("%s: failed looking up symbol %s\n", pathname().c_str(), demangle(name).c_str());
}
}
return ret;
}
// symbol_other(idx) is similar to symbol(idx), except that the symbol is not
// looked up in the object itself, just in the other objects.
symbol_module object::symbol_other(unsigned idx)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
assert(dynamic_val(DT_SYMENT) == sizeof(Elf64_Sym));
auto sym = &symtab[idx];
auto nameidx = sym->st_name;
auto name = dynamic_ptr<const char>(DT_STRTAB) + nameidx;
symbol_module ret(nullptr,nullptr);
_prog.with_modules([&](const elf::program::modules_list &ml) {
for (auto module : ml.objects) {
if (module == this)
continue; // do not match this module
if (auto sym = module->lookup_symbol(name, false)) {
ret = symbol_module(sym, module);
break;
}
}
});
if (!ret.symbol) {
abort("%s: failed looking up symbol %s in other objects\n",
pathname().c_str(), demangle(name).c_str());
}
return ret;
}
void object::relocate_rela()
{
if(has_non_writable_text_relocations()) {
make_text_writable(true);
}
auto rela = dynamic_ptr<Elf64_Rela>(DT_RELA);
assert(dynamic_val(DT_RELAENT) == sizeof(Elf64_Rela));
unsigned nb = dynamic_val(DT_RELASZ) / sizeof(Elf64_Rela);
for (auto p = rela; p < rela + nb; ++p) {
auto info = p->r_info;
u32 sym = info >> 32;
u32 type = info & 0xffffffff;
void *addr = _base + p->r_offset;
auto addend = p->r_addend;
if (!arch_relocate_rela(type, sym, addr, addend)) {
debug_early_u64("relocate_rela(): unknown relocation type ", type);
abort();
}
}
elf_debug("Relocated %d symbols in DT_RELA\n", nb);
}
extern "C" { void __elf_resolve_pltgot(void); }
void object::relocate_pltgot()
{
auto pltgot = dynamic_ptr<void*>(DT_PLTGOT);
void *original_plt = nullptr;
if (pltgot[1]) {
// The library was prelinked before being copied to OSV, so the
// .GOT.PLT entries point not to the .PLT but to a prelinked address
// of the actual function. We'll need to return the link to the .PLT.
// The prelinker saved us in pltgot[1] the address of .plt + 0x16.
#ifdef AARCH64_PORT_STUB
assert(0);
#endif /* AARCH64_PORT_STUB */
original_plt = static_cast<void*>(_base + (u64)pltgot[1]);
}
bool bind_now = dynamic_exists(DT_BIND_NOW) || mlocked() ||
(dynamic_exists(DT_FLAGS) && (dynamic_val(DT_FLAGS) & DF_BIND_NOW)) ||
(dynamic_exists(DT_FLAGS_1) && (dynamic_val(DT_FLAGS_1) & DF_1_NOW));
auto rel = dynamic_ptr<Elf64_Rela>(DT_JMPREL);
auto nrel = dynamic_val(DT_PLTRELSZ) / sizeof(*rel);
for (auto p = rel; p < rel + nrel; ++p) {
auto info = p->r_info;
u32 type = info & 0xffffffff;
assert(type == ARCH_JUMP_SLOT);
void *addr = _base + p->r_offset;
if (bind_now) {
// If on-load binding is requested (instead of the default lazy
// binding), try to resolve all the PLT entries now.
// If symbol cannot be resolved warn about it instead of aborting
u32 sym = info >> 32;
auto _sym = symbol(sym, true);
if (arch_relocate_jump_slot(_sym, addr, p->r_addend))
continue;
}
if (original_plt) {
// Restore the link to the original plt.
// We know the JUMP_SLOT entries are in plt order, and that
// each plt entry is 16 bytes.
*static_cast<void**>(addr) = original_plt + (p-rel)*16;
} else {
// The JUMP_SLOT entry already points back to the PLT, just
// make sure it is relocated relative to the object base.
*static_cast<u64*>(addr) += reinterpret_cast<u64>(_base);
}
}
elf_debug("Relocated %d PLT symbols in DT_JMPREL\n", nrel);
// PLTGOT resolution has a special calling convention,
// for x64 the symbol index and some word is pushed on the stack,
// for AArch64 &pltgot[n] and LR are pushed on the stack,
// so we need an assembly stub to convert it back to the
// standard calling convention.
pltgot[1] = this;
pltgot[2] = reinterpret_cast<void*>(__elf_resolve_pltgot);
}
void* object::resolve_pltgot(unsigned index)
{
assert(sched::preemptable());
auto rel = dynamic_ptr<Elf64_Rela>(DT_JMPREL);
auto slot = rel[index];
auto info = slot.r_info;
u32 sym = info >> 32;
u32 type = info & 0xffffffff;
assert(type == ARCH_JUMP_SLOT);
void *addr = _base + slot.r_offset;
auto sm = symbol(sym);
if (sm.obj != this) {
WITH_LOCK(_used_by_resolve_plt_got_mutex) {
_used_by_resolve_plt_got.insert(sm.obj->shared_from_this());
}
}
if (!arch_relocate_jump_slot(sm, addr, slot.r_addend)) {
debug_early("resolve_pltgot(): failed jump slot relocation\n");
abort();
}
return *static_cast<void**>(addr);
}
void object::relocate()
{
assert(!dynamic_exists(DT_REL));
if (dynamic_exists(DT_RELA)) {
relocate_rela();
}
if (dynamic_exists(DT_JMPREL)) {
relocate_pltgot();
}
}
unsigned long
elf64_hash(const char *name)
{
unsigned long h = 0, g;
while (*name) {
h = (h << 4) + (unsigned char)(*name++);
if ((g = h & 0xf0000000)) {
h ^= g >> 24;
}
h &= 0x0fffffff;
}
return h;
}
constexpr Elf64_Versym old_version_symbol_mask = Elf64_Versym(1) << 15;
Elf64_Sym* object::lookup_symbol_old(const char* name)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
auto strtab = dynamic_ptr<char>(DT_STRTAB);
auto hashtab = dynamic_ptr<Elf64_Word>(DT_HASH);
auto nbucket = hashtab[0];
auto buckets = hashtab + 2;
auto chain = buckets + nbucket;
for (auto ent = buckets[elf64_hash(name) % nbucket];
ent != STN_UNDEF;
ent = chain[ent]) {
auto &sym = symtab[ent];
if (strcmp(name, &strtab[sym.st_name]) == 0) {
return &sym;
}
}
return nullptr;
}
uint_fast32_t
dl_new_hash(const char *s)
{
uint_fast32_t h = 5381;
for (unsigned char c = *s; c != '\0'; c = *++s) {
h = h * 33 + c;
}
return h & 0xffffffff;
}
Elf64_Sym* object::lookup_symbol_gnu(const char* name, bool self_lookup)
{
auto symtab = dynamic_ptr<Elf64_Sym>(DT_SYMTAB);
auto strtab = dynamic_ptr<char>(DT_STRTAB);
auto hashtab = dynamic_ptr<Elf64_Word>(DT_GNU_HASH);
auto nbucket = hashtab[0];
auto symndx = hashtab[1];
auto maskwords = hashtab[2];
auto shift2 = hashtab[3];
auto bloom = reinterpret_cast<const Elf64_Xword*>(hashtab + 4);
auto C = sizeof(*bloom) * 8;
auto hashval = dl_new_hash(name);
auto bword = bloom[(hashval / C) % maskwords];
auto hashbit1 = hashval % C;
auto hashbit2 = (hashval >> shift2) % C;
if ((bword >> hashbit1) == 0 || (bword >> hashbit2) == 0) {
return nullptr;
}
auto buckets = reinterpret_cast<const Elf64_Word*>(bloom + maskwords);
auto chains = buckets + nbucket - symndx;
auto idx = buckets[hashval % nbucket];
if (idx == 0) {
return nullptr;
}
auto version_symtab = (!self_lookup && dynamic_exists(DT_VERSYM)) ? dynamic_ptr<Elf64_Versym>(DT_VERSYM) : nullptr;
do {
if ((chains[idx] & ~1) != (hashval & ~1)) {
continue;
}
if (version_symtab && version_symtab[idx] & old_version_symbol_mask) { //Ignore old version symbols
continue;
}
if (strcmp(&strtab[symtab[idx].st_name], name) == 0) {
return &symtab[idx];
}
} while ((chains[idx++] & 1) == 0);
return nullptr;
}
Elf64_Sym* object::lookup_symbol(const char* name, bool self_lookup)
{
if (!visible()) {
return nullptr;
}
Elf64_Sym* sym;
if (dynamic_exists(DT_GNU_HASH)) {
sym = lookup_symbol_gnu(name, self_lookup);
} else {
sym = lookup_symbol_old(name);
}
if (sym && sym->st_shndx == SHN_UNDEF) {
sym = nullptr;
}
return sym;
}
symbol_module object::lookup_symbol_deep(const char* name)
{
symbol_module sym = { lookup_symbol(name, false), this };
if (!sym.symbol) {
auto deps = this->collect_dependencies_bfs();
for (auto&& _obj : deps) {
auto symbol = _obj->lookup_symbol(name, false);
if (symbol) {
sym = { symbol, _obj };
break;
}
}
}
return sym;
}
unsigned object::symtab_len()
{
if (dynamic_exists(DT_HASH)) {
auto hashtab = dynamic_ptr<Elf64_Word>(DT_HASH);
return hashtab[1];
}
auto hashtab = dynamic_ptr<Elf64_Word>(DT_GNU_HASH);
auto nbucket = hashtab[0];
auto symndx = hashtab[1];
auto maskwords = hashtab[2];
auto bloom = reinterpret_cast<const Elf64_Xword*>(hashtab + 4);
auto buckets = reinterpret_cast<const Elf64_Word*>(bloom + maskwords);
auto chains = buckets + nbucket - symndx;
unsigned len = 0;
for (unsigned b = 0; b < nbucket; ++b) {
auto idx = buckets[b];
if (idx == 0) {
continue;
}
do {
++len;
} while ((chains[idx++] & 1) == 0);
}
return len;
}
dladdr_info object::lookup_addr(const void* addr)
{
dladdr_info ret;
if (addr < _base || addr >= _end) {