Loader: Support loading non-position independent executables

Author: https://github.com/itamar8910
Commit: https://github.com/SerenityOS/serenity/commit/a83a9f3a55a

Libraries/LibELF/DynamicLoader.cpp

@@ -144,9 +144,10 @@ void* DynamicLoader::symbol_for_name(const char* name)
 RefPtr<DynamicObject> DynamicLoader::load_from_image(unsigned flags, size_t total_tls_size)
 {
 
-    m_valid = m_elf_image.is_valid() && m_elf_image.is_dynamic();
+    m_valid = m_elf_image.is_valid();
 
     if (!m_valid) {
+        dbgprintf("DynamicLoader::load_from_image failed: image is invalid\n");
         return nullptr;
     }
 
@@ -163,8 +164,10 @@ RefPtr<DynamicObject> DynamicLoader::load_from_image(unsigned flags, size_t tota
     m_dynamic_object->m_global_symbol_lookup_func = m_global_symbol_lookup_func;
 
     auto rc = load_stage_2(flags, total_tls_size);
-    if (!rc)
+    if (!rc) {
+        dbgprintf("DynamicLoader::load_from_image failed at load_stage_2\n");
         return nullptr;
+    }
     return m_dynamic_object;
 }
 
@@ -235,7 +238,9 @@ void DynamicLoader::load_program_headers()
 
     // Process regions in order: .text, .data, .tls
     auto* region = text_region_ptr;
-    void* text_segment_begin = mmap_with_name(nullptr,
+    void* requested_load_address = m_elf_image.is_dynamic() ? nullptr : region->desired_load_address().as_ptr();
+    void* text_segment_begin = mmap_with_name(
+        requested_load_address,
         region->required_load_size(),
         region->mmap_prot(),
         MAP_PRIVATE,
@@ -245,13 +250,18 @@ void DynamicLoader::load_program_headers()
     if (MAP_FAILED == text_segment_begin) {
         ASSERT_NOT_REACHED();
     }
+    ASSERT(requested_load_address == nullptr || requested_load_address == text_segment_begin);
     m_text_segment_size = region->required_load_size();
     m_text_segment_load_address = VirtualAddress { (FlatPtr)text_segment_begin };
 
-    m_dynamic_section_address = dynamic_region_desired_vaddr.offset(m_text_segment_load_address.get());
+    if (m_elf_image.is_dynamic())
+        m_dynamic_section_address = dynamic_region_desired_vaddr.offset(m_text_segment_load_address.get());
+    else
+        m_dynamic_section_address = dynamic_region_desired_vaddr;
 
     region = data_region_ptr;
-    void* data_segment_begin = mmap_with_name((u8*)text_segment_begin + m_text_segment_size,
+    void* data_segment_begin = mmap_with_name(
+        (u8*)text_segment_begin + m_text_segment_size,
         region->required_load_size(),
         region->mmap_prot(),
         MAP_ANONYMOUS | MAP_PRIVATE,
@@ -261,10 +271,14 @@ void DynamicLoader::load_program_headers()
     if (MAP_FAILED == data_segment_begin) {
         ASSERT_NOT_REACHED();
     }
-    VirtualAddress data_segment_actual_addr = region->desired_load_address().offset((FlatPtr)text_segment_begin);
+    VirtualAddress data_segment_actual_addr;
+    if (m_elf_image.is_dynamic()) {
+        data_segment_actual_addr = region->desired_load_address().offset((FlatPtr)text_segment_begin);
+    } else {
+        data_segment_actual_addr = region->desired_load_address();
+    }
     memcpy(data_segment_actual_addr.as_ptr(), (u8*)m_file_mapping + region->offset(), region->size_in_image());
-
-    // FIXME: Initialize the values in the TLS section. Currently, it will always be zeroed.
+    // FIXME: Initialize the values in the TLS section. Currently, it is zeroed.
 }
 
 void DynamicLoader::do_relocations(size_t total_tls_size)
@@ -272,7 +286,12 @@ void DynamicLoader::do_relocations(size_t total_tls_size)
     auto main_relocation_section = m_dynamic_object->relocation_section();
     main_relocation_section.for_each_relocation([&](ELF::DynamicObject::Relocation relocation) {
         VERBOSE("Relocation symbol: %s, type: %d\n", relocation.symbol().name(), relocation.type());
-        u32* patch_ptr = (u32*)(m_dynamic_object->base_address().as_ptr() + relocation.offset());
+        FlatPtr* patch_ptr = nullptr;
+        if (is_dynamic())
+            patch_ptr = (FlatPtr*)(m_dynamic_object->base_address().as_ptr() + relocation.offset());
+        else
+            patch_ptr = (FlatPtr*)(FlatPtr)relocation.offset();
+
         // VERBOSE("dynamic object name: %s\n", dynamic_object.object_name());
         VERBOSE("dynamic object base address: %p\n", m_dynamic_object->base_address());
         VERBOSE("relocation offset: 0x%x\n", relocation.offset());
@@ -393,13 +412,12 @@ void DynamicLoader::do_relocations(size_t total_tls_size)
             VERBOSE("patching plt reloaction: 0x%x\n", relocation.offset_in_section());
             [[maybe_unused]] auto rc = m_dynamic_object->patch_plt_entry(relocation.offset_in_section());
         } else {
-            // LAZY-ily bind the PLT slots by just adding the base address to the offsets stored there
-            // This avoids doing symbol lookup, which might be expensive
             ASSERT(relocation.type() == R_386_JMP_SLOT);
 
             u8* relocation_address = relocation.address().as_ptr();
 
-            *(u32*)relocation_address += (FlatPtr)m_dynamic_object->base_address().as_ptr();
+            if (m_elf_image.is_dynamic())
+                *(u32*)relocation_address += (FlatPtr)m_dynamic_object->base_address().as_ptr();
         }
         return IterationDecision::Continue;
     });

Libraries/LibELF/DynamicLoader.h

@@ -79,6 +79,7 @@ public:
     void set_global_symbol_lookup_function(DynamicObject::SymbolLookupFunction func) { m_global_symbol_lookup_func = func; }
 
     VirtualAddress text_segment_load_address() const { return m_text_segment_load_address; }
+    bool is_dynamic() const { return m_elf_image.is_dynamic(); }
 
 private:
     class ProgramHeaderRegion {

Libraries/LibELF/DynamicObject.cpp

@@ -50,6 +50,14 @@ DynamicObject::DynamicObject(VirtualAddress base_address, VirtualAddress dynamic
     : m_base_address(base_address)
     , m_dynamic_address(dynamic_section_addresss)
 {
+    Elf32_Ehdr* header = (Elf32_Ehdr*)base_address.as_ptr();
+    Elf32_Phdr* pheader = (Elf32_Phdr*)(base_address.as_ptr() + header->e_phoff);
+    m_elf_base_address = VirtualAddress(pheader->p_vaddr - pheader->p_offset);
+    if (header->e_type == ET_DYN)
+        m_is_elf_dynamic = true;
+    else
+        m_is_elf_dynamic = false;
+
     parse();
 }
 
@@ -82,31 +90,31 @@ void DynamicObject::parse()
     for_each_dynamic_entry([&](const DynamicEntry& entry) {
         switch (entry.tag()) {
         case DT_INIT:
-            m_init_offset = entry.ptr();
+            m_init_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_FINI:
-            m_fini_offset = entry.ptr();
+            m_fini_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_INIT_ARRAY:
-            m_init_array_offset = entry.ptr();
+            m_init_array_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_INIT_ARRAYSZ:
             m_init_array_size = entry.val();
             break;
         case DT_FINI_ARRAY:
-            m_fini_array_offset = entry.ptr();
+            m_fini_array_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_FINI_ARRAYSZ:
             m_fini_array_size = entry.val();
             break;
         case DT_HASH:
-            m_hash_table_offset = entry.ptr();
+            m_hash_table_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_SYMTAB:
-            m_symbol_table_offset = entry.ptr();
+            m_symbol_table_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_STRTAB:
-            m_string_table_offset = entry.ptr();
+            m_string_table_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_STRSZ:
             m_size_of_string_table = entry.val();
@@ -115,7 +123,7 @@ void DynamicObject::parse()
             m_size_of_symbol_table_entry = entry.val();
             break;
         case DT_PLTGOT:
-            m_procedure_linkage_table_offset = entry.ptr();
+            m_procedure_linkage_table_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_PLTRELSZ:
             m_size_of_plt_relocation_entry_list = entry.val();
@@ -125,11 +133,11 @@ void DynamicObject::parse()
             ASSERT(m_procedure_linkage_table_relocation_type & (DT_REL | DT_RELA));
             break;
         case DT_JMPREL:
-            m_plt_relocation_offset_location = entry.ptr();
+            m_plt_relocation_offset_location = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_RELA:
         case DT_REL:
-            m_relocation_table_offset = entry.ptr();
+            m_relocation_table_offset = entry.ptr() - (FlatPtr)m_elf_base_address.as_ptr();
             break;
         case DT_RELASZ:
         case DT_RELSZ:
@@ -171,12 +179,13 @@ void DynamicObject::parse()
 
     if (!m_size_of_relocation_entry) {
         // TODO: FIXME, this shouldn't be hardcoded
-        // The reason we need this here is the for some reason, when there only PLT relocations, the compiler
+        // The reason we need this here is that for some reason, when there only PLT relocations, the compiler
         // doesn't insert a 'PLTRELSZ' entry to the dynamic section
         m_size_of_relocation_entry = sizeof(Elf32_Rel);
     }
 
     auto hash_section_address = hash_section().address().as_ptr();
+    // TODO: consider base address - it might not be zero
     auto num_hash_chains = ((u32*)hash_section_address)[1];
     m_symbol_count = num_hash_chains;
 }
@@ -287,9 +296,7 @@ const DynamicObject::Symbol DynamicObject::HashSection::lookup_symbol(const char
     for (u32 i = buckets[hash_value % num_buckets]; i; i = chains[i]) {
         auto symbol = m_dynamic.symbol(i);
         if (strcmp(name, symbol.name()) == 0) {
-#ifdef DYNAMIC_LOAD_DEBUG
-            dbgprintf("Returning dynamic symbol with index %u for %s: %p\n", i, symbol.name(), symbol.address().as_ptr());
-#endif
+            VERBOSE("Returning dynamic symbol with index %u for %s: %p\n", i, symbol.name(), symbol.address().as_ptr());
             return symbol;
         }
     }

Libraries/LibELF/DynamicObject.h

@@ -105,7 +105,12 @@ public:
         {
             return m_is_undefined;
         }
-        VirtualAddress address() const { return m_dynamic.base_address().offset(value()); }
+        VirtualAddress address() const
+        {
+            if (m_dynamic.elf_is_dynamic())
+                return m_dynamic.base_address().offset(value());
+            return VirtualAddress { value() };
+        }
         const DynamicObject& object() const { return m_dynamic; }
 
     private:
@@ -135,7 +140,10 @@ public:
         {
             return !entry_size() ? 0 : size() / entry_size();
         }
-        VirtualAddress address() const { return m_dynamic.base_address().offset(m_section_offset); }
+        VirtualAddress address() const
+        {
+            return m_dynamic.base_address().offset(m_section_offset);
+        }
 
     protected:
         friend class RelocationSection;
@@ -176,7 +184,12 @@ public:
         unsigned type() const { return ELF32_R_TYPE(m_rel.r_info); }
         unsigned symbol_index() const { return ELF32_R_SYM(m_rel.r_info); }
         const Symbol symbol() const { return m_dynamic.symbol(symbol_index()); }
-        VirtualAddress address() const { return m_dynamic.base_address().offset(offset()); }
+        VirtualAddress address() const
+        {
+            if (m_dynamic.elf_is_dynamic())
+                return m_dynamic.base_address().offset(offset());
+            return VirtualAddress { offset() };
+        }
 
     private:
         const DynamicObject& m_dynamic;
@@ -274,6 +287,8 @@ public:
     using SymbolLookupFunction = DynamicObject::SymbolLookupResult (*)(const char*);
     SymbolLookupFunction m_global_symbol_lookup_func { nullptr };
 
+    bool elf_is_dynamic() const { return m_is_elf_dynamic; }
+
 private:
     explicit DynamicObject(VirtualAddress base_address, VirtualAddress dynamic_section_address);
 
@@ -288,6 +303,7 @@ private:
 
     VirtualAddress m_base_address;
     VirtualAddress m_dynamic_address;
+    VirtualAddress m_elf_base_address;
 
     unsigned m_symbol_count { 0 };
 
@@ -318,6 +334,7 @@ private:
     size_t m_size_of_relocation_entry { 0 };
     size_t m_size_of_relocation_table { 0 };
     FlatPtr m_relocation_table_offset { 0 };
+    bool m_is_elf_dynamic { false };
 
     // DT_FLAGS
     Elf32_Word m_dt_flags { 0 };
@@ -356,7 +373,6 @@ inline void DynamicObject::for_each_dynamic_entry(F func) const
 {
     auto* dyns = reinterpret_cast<const Elf32_Dyn*>(m_dynamic_address.as_ptr());
     for (unsigned i = 0;; ++i) {
-        // dbgprintf("%d\n", i);
         auto&& dyn = DynamicEntry(dyns[i]);
         if (dyn.tag() == DT_NULL)
             break;

Userland/DynamicLoader/main.cpp

@@ -107,6 +107,7 @@ static void perform_self_relocations(auxv_t* auxvp)
     dynamic_object->relocation_section().for_each_relocation([base_address](auto& reloc) {
         if (reloc.type() != R_386_RELATIVE)
             return IterationDecision::Continue;
+
         *(u32*)reloc.address().as_ptr() += base_address;
         return IterationDecision::Continue;
     });
@@ -171,10 +172,10 @@ static Vector<String> get_dependencies(const String& name)
 
 static void map_dependencies(const String& name)
 {
-    VERBOSE("mapping dependencies for: %s", name.characters());
+    VERBOSE("mapping dependencies for: %s\n", name.characters());
 
     for (const auto& needed_name : get_dependencies(name)) {
-        VERBOSE("needed library: %s", needed_name.characters());
+        VERBOSE("needed library: %s\n", needed_name.characters());
         String library_name = get_library_name(needed_name);
 
         if (!g_loaders.contains(library_name)) {
@@ -193,7 +194,7 @@ static void allocate_tls()
     }
     if (total_tls_size) {
         [[maybe_unused]] void* tls_address = allocate_tls(total_tls_size);
-        VERBOSE("from userspace, tls_address: %p", tls_address);
+        VERBOSE("from userspace, tls_address: %p\n", tls_address);
     }
     g_total_tls_size = total_tls_size;
 }
@@ -224,17 +225,17 @@ static void initialize_libc()
 
 static void load_elf(const String& name)
 {
-    VERBOSE("load_elf: %s", name.characters());
+    VERBOSE("load_elf: %s\n", name.characters());
     auto loader = g_loaders.get(name).value();
+    VERBOSE("a1\n");
     for (const auto& needed_name : get_dependencies(name)) {
-        VERBOSE("needed library: %s", needed_name.characters());
+        VERBOSE("needed library: %s\n", needed_name.characters());
         String library_name = get_library_name(needed_name);
         if (!g_loaded_objects.contains(library_name)) {
             load_elf(library_name);
         }
     }
 
-    VERBOSE("loading: %s", name.characters());
     auto dynamic_object = loader->load_from_image(RTLD_GLOBAL | RTLD_LAZY, g_total_tls_size);
     ASSERT(!dynamic_object.is_null());
     g_loaded_objects.set(name, dynamic_object.release_nonnull());
@@ -270,7 +271,7 @@ static FlatPtr loader_main(auxv_t* auxvp)
 
     VERBOSE("loaded all dependencies");
     for ([[maybe_unused]] auto& lib : g_loaders) {
-        VERBOSE("%s - tls size: %u, tls offset: %u", lib.key.characters(), lib.value->tls_size(), lib.value->tls_offset());
+        VERBOSE("%s - tls size: %u, tls offset: %u\n", lib.key.characters(), lib.value->tls_size(), lib.value->tls_offset());
     }
 
     allocate_tls();
@@ -278,8 +279,12 @@ static FlatPtr loader_main(auxv_t* auxvp)
     load_elf(main_program_name);
 
     auto main_program_lib = g_loaders.get(main_program_name).value();
-    FlatPtr entry_point = reinterpret_cast<FlatPtr>(main_program_lib->image().entry().as_ptr() + (FlatPtr)main_program_lib->text_segment_load_address().as_ptr());
-    VERBOSE("entry point: %p", entry_point);
+
+    FlatPtr entry_point = reinterpret_cast<FlatPtr>(main_program_lib->image().entry().as_ptr());
+    if (main_program_lib->is_dynamic())
+        entry_point += reinterpret_cast<FlatPtr>(main_program_lib->text_segment_load_address().as_ptr());
+
+    VERBOSE("entry point: %p\n", entry_point);
 
     // This will unmap the temporary memory maps we had for loading the libraries
     clear_temporary_objects_mappings();
@@ -310,9 +315,9 @@ void _start(int argc, char** argv, char** envp)
     }
 
     MainFunction main_function = (MainFunction)(entry);
-    VERBOSE("jumping to main program entry point: %p", main_function);
+    VERBOSE("jumping to main program entry point: %p\n", main_function);
     int rc = main_function(argc, argv, envp);
-    VERBOSE("rc: %d", rc);
+    VERBOSE("rc: %d\n", rc);
     if (g_libc_exit != nullptr) {
         g_libc_exit(rc);
     } else {