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https://github.com/RGBCube/serenity
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Loader: Add dynamic loader program
The dynamic loader exists as /usr/lib/Loader.so and is loaded by the kernel when ET_DYN programs are executed. The dynamic loader is responsible for loading the dependencies of the main program, allocating TLS storage, preparing all loaded objects for execution and finally jumping to the entry of the main program.
This commit is contained in:
Itamar
Andreas Kling
parent
781aa424a9
commit
07b4957361
18 changed files with 962 additions and 104 deletions
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@ -1,5 +1,6 @@
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/*
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* Copyright (c) 2019-2020, Andrew Kaster <andrewdkaster@gmail.com>
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* Copyright (c) 2020, Itamar S. <itamar8910@gmail.com>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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@ -27,14 +28,16 @@
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#pragma once
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#include <AK/Assertions.h>
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#include <AK/RefCounted.h>
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#include <Kernel/VirtualAddress.h>
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#include <LibELF/exec_elf.h>
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namespace ELF {
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class DynamicObject {
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class DynamicObject : public RefCounted<DynamicObject> {
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public:
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explicit DynamicObject(VirtualAddress base_address, VirtualAddress dynamic_section_address);
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static NonnullRefPtr<DynamicObject> construct(VirtualAddress base_address, VirtualAddress dynamic_section_address);
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~DynamicObject();
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void dump() const;
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@ -69,6 +72,23 @@ public:
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, m_sym(sym)
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, m_index(index)
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{
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if (section_index() == 0)
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m_is_undefined = true;
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}
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Symbol(const Symbol& other)
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: m_dynamic(other.m_dynamic)
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, m_sym(other.m_sym)
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, m_index(other.m_index)
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, m_is_undefined(other.m_is_undefined)
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{
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}
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static Symbol create_undefined(const DynamicObject& dynamic)
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{
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auto s = Symbol(dynamic, 0, {});
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s.m_is_undefined = true;
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return s;
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}
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~Symbol() { }
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@ -80,13 +100,19 @@ public:
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unsigned index() const { return m_index; }
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unsigned type() const { return ELF32_ST_TYPE(m_sym.st_info); }
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unsigned bind() const { return ELF32_ST_BIND(m_sym.st_info); }
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bool is_undefined() const { return this == &m_dynamic.the_undefined_symbol(); }
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bool is_undefined() const
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{
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return m_is_undefined;
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}
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VirtualAddress address() const { return m_dynamic.base_address().offset(value()); }
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const DynamicObject& object() const { return m_dynamic; }
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private:
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const DynamicObject& m_dynamic;
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const Elf32_Sym& m_sym;
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const unsigned m_index;
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bool m_is_undefined { false };
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};
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class Section {
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@ -105,7 +131,10 @@ public:
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unsigned offset() const { return m_section_offset; }
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unsigned size() const { return m_section_size_bytes; }
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unsigned entry_size() const { return m_entry_size; }
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unsigned entry_count() const { return !entry_size() ? 0 : size() / entry_size(); }
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unsigned entry_count() const
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{
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return !entry_size() ? 0 : size() / entry_size();
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}
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VirtualAddress address() const { return m_dynamic.base_address().offset(m_section_offset); }
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protected:
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@ -191,9 +220,13 @@ public:
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unsigned symbol_count() const { return m_symbol_count; }
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const Symbol symbol(unsigned) const;
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const Symbol& the_undefined_symbol() const { return m_the_undefined_symbol; }
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typedef void (*InitializationFunction)();
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bool has_init_section() const { return m_init_offset != 0; }
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bool has_init_array_section() const { return m_init_array_offset != 0; }
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const Section init_section() const;
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InitializationFunction init_section_function() const;
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const Section fini_section() const;
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const Section init_array_section() const;
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const Section fini_array_section() const;
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@ -215,7 +248,28 @@ public:
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const char* soname() const { return m_has_soname ? symbol_string_table_string(m_soname_index) : nullptr; }
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Optional<FlatPtr> tls_offset() const { return m_tls_offset; }
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Optional<FlatPtr> tls_size() const { return m_tls_size; }
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void set_tls_offset(FlatPtr offset) { m_tls_offset = offset; }
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void set_tls_size(FlatPtr size) { m_tls_size = size; }
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template<typename F>
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void for_each_needed_library(F) const;
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template<typename F>
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void for_each_initialization_array_function(F f) const;
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struct SymbolLookupResult {
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bool found { false };
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FlatPtr value { 0 };
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FlatPtr address { 0 };
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const ELF::DynamicObject* dynamic_object { nullptr }; // The object in which the symbol is defined
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};
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Optional<SymbolLookupResult> lookup_symbol(const char* name) const;
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private:
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explicit DynamicObject(VirtualAddress base_address, VirtualAddress dynamic_section_address);
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const char* symbol_string_table_string(Elf32_Word) const;
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void parse();
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@ -227,7 +281,6 @@ private:
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VirtualAddress m_base_address;
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VirtualAddress m_dynamic_address;
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Symbol m_the_undefined_symbol { *this, 0, {} };
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unsigned m_symbol_count { 0 };
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@ -264,6 +317,9 @@ private:
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bool m_has_soname { false };
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Elf32_Word m_soname_index { 0 }; // Index into dynstr table for SONAME
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Optional<FlatPtr> m_tls_offset;
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Optional<FlatPtr> m_tls_size;
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// End Section information from DT_* entries
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};
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@ -271,7 +327,10 @@ template<typename F>
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inline void DynamicObject::RelocationSection::for_each_relocation(F func) const
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{
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for (unsigned i = 0; i < relocation_count(); ++i) {
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if (func(relocation(i)) == IterationDecision::Break)
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const auto reloc = relocation(i);
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if (reloc.type() == 0)
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continue;
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if (func(reloc) == IterationDecision::Break)
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break;
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}
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}
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@ -290,6 +349,7 @@ inline void DynamicObject::for_each_dynamic_entry(F func) const
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{
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auto* dyns = reinterpret_cast<const Elf32_Dyn*>(m_dynamic_address.as_ptr());
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for (unsigned i = 0;; ++i) {
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// dbgprintf("%d\n", i);
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auto&& dyn = DynamicEntry(dyns[i]);
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if (dyn.tag() == DT_NULL)
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break;
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@ -297,5 +357,30 @@ inline void DynamicObject::for_each_dynamic_entry(F func) const
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break;
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}
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}
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template<typename F>
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inline void DynamicObject::for_each_needed_library(F func) const
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{
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for_each_dynamic_entry([func, this](auto entry) {
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if (entry.tag() != DT_NEEDED)
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return IterationDecision::Continue;
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Elf32_Word offset = entry.val();
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const char* name = (const char*)(m_base_address.offset(m_string_table_offset).offset(offset)).as_ptr();
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if (func(StringView(name)) == IterationDecision::Break)
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return IterationDecision::Break;
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return IterationDecision::Continue;
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});
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}
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template<typename F>
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void DynamicObject::for_each_initialization_array_function(F f) const
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{
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if (!has_init_array_section())
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return;
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FlatPtr init_array = (FlatPtr)init_array_section().address().as_ptr();
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for (size_t i = 0; i < (m_init_array_size / sizeof(void*)); ++i) {
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InitializationFunction current = ((InitializationFunction*)(init_array))[i];
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f(current);
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}
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}
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} // end namespace ELF
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