aboutsummaryrefslogtreecommitdiffstats
path: root/com32/lib/sys/module/elf_module.c
diff options
context:
space:
mode:
Diffstat (limited to 'com32/lib/sys/module/elf_module.c')
-rw-r--r--com32/lib/sys/module/elf_module.c488
1 files changed, 488 insertions, 0 deletions
diff --git a/com32/lib/sys/module/elf_module.c b/com32/lib/sys/module/elf_module.c
new file mode 100644
index 00000000..4b1f2bbd
--- /dev/null
+++ b/com32/lib/sys/module/elf_module.c
@@ -0,0 +1,488 @@
+/*
+ * elf_module.c
+ *
+ * Created on: Aug 11, 2008
+ * Author: Stefan Bucur <stefanb@zytor.com>
+ */
+
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <elf.h>
+
+#include <linux/list.h>
+#include <sys/module.h>
+
+#include "elfutils.h"
+#include "common.h"
+
+
+static int check_header(Elf32_Ehdr *elf_hdr) {
+ int res;
+
+ res = check_header_common(elf_hdr);
+
+ if (res != 0)
+ return res;
+
+ if (elf_hdr->e_type != MODULE_ELF_TYPE) {
+ DBG_PRINT("The ELF file must be a shared object\n");
+ return -1;
+ }
+
+ if (elf_hdr->e_phoff == 0x00000000) {
+ DBG_PRINT("PHT missing\n");
+ return -1;
+ }
+
+ return 0;
+}
+
+/*
+ *
+ * The implementation assumes that the loadable segments are present
+ * in the PHT sorted by their offsets, so that only forward seeks would
+ * be necessary.
+ */
+static int load_segments(struct elf_module *module, Elf32_Ehdr *elf_hdr) {
+ int i;
+ int res = 0;
+ void *pht = NULL;
+ Elf32_Phdr *cr_pht;
+
+ Elf32_Addr min_addr = 0x00000000; // Min. ELF vaddr
+ Elf32_Addr max_addr = 0x00000000; // Max. ELF vaddr
+ Elf32_Word max_align = sizeof(void*); // Min. align of posix_memalign()
+ Elf32_Addr min_alloc, max_alloc; // Min. and max. aligned allocables
+
+ Elf32_Addr dyn_addr = 0x00000000;
+
+ // Get to the PHT
+ image_seek(elf_hdr->e_phoff, module);
+
+ // Load the PHT
+ pht = malloc(elf_hdr->e_phnum * elf_hdr->e_phentsize);
+ image_read(pht, elf_hdr->e_phnum * elf_hdr->e_phentsize, module);
+
+ // Compute the memory needings of the module
+ for (i=0; i < elf_hdr->e_phnum; i++) {
+ cr_pht = (Elf32_Phdr*)(pht + i * elf_hdr->e_phentsize);
+
+ switch (cr_pht->p_type) {
+ case PT_LOAD:
+ if (i == 0) {
+ min_addr = cr_pht->p_vaddr;
+ } else {
+ min_addr = MIN(min_addr, cr_pht->p_vaddr);
+ }
+
+ max_addr = MAX(max_addr, cr_pht->p_vaddr + cr_pht->p_memsz);
+ max_align = MAX(max_align, cr_pht->p_align);
+ break;
+ case PT_DYNAMIC:
+ dyn_addr = cr_pht->p_vaddr;
+ break;
+ default:
+ // Unsupported - ignore
+ break;
+ }
+ }
+
+ if (max_addr - min_addr == 0) {
+ // No loadable segments
+ DBG_PRINT("No loadable segments found\n");
+ goto out;
+ }
+
+ if (dyn_addr == 0) {
+ DBG_PRINT("No dynamic information segment found\n");
+ goto out;
+ }
+
+ // The minimum address that should be allocated
+ min_alloc = min_addr - (min_addr % max_align);
+
+ // The maximum address that should be allocated
+ max_alloc = max_addr - (max_addr % max_align);
+ if (max_addr % max_align > 0)
+ max_alloc += max_align;
+
+
+ if (elf_malloc(&module->module_addr,
+ max_align,
+ max_alloc-min_alloc) != 0) {
+
+ DBG_PRINT("Could not allocate segments\n");
+ goto out;
+ }
+
+ module->base_addr = (Elf32_Addr)(module->module_addr) - min_alloc;
+ module->module_size = max_alloc - min_alloc;
+
+ // Zero-initialize the memory
+ memset(module->module_addr, 0, module->module_size);
+
+ for (i = 0; i < elf_hdr->e_phnum; i++) {
+ cr_pht = (Elf32_Phdr*)(pht + i * elf_hdr->e_phentsize);
+
+ if (cr_pht->p_type == PT_LOAD) {
+ // Copy the segment at its destination
+ if (cr_pht->p_offset < module->_cr_offset) {
+ // The segment contains data before the current offset
+ // It can be discarded without worry - it would contain only
+ // headers
+ Elf32_Off aux_off = module->_cr_offset - cr_pht->p_offset;
+
+ if (image_read(module_get_absolute(cr_pht->p_vaddr, module) + aux_off,
+ cr_pht->p_filesz - aux_off, module) < 0) {
+ res = -1;
+ goto out;
+ }
+ } else {
+ if (image_seek(cr_pht->p_offset, module) < 0) {
+ res = -1;
+ goto out;
+ }
+
+ if (image_read(module_get_absolute(cr_pht->p_vaddr, module),
+ cr_pht->p_filesz, module) < 0) {
+ res = -1;
+ goto out;
+ }
+ }
+
+ DBG_PRINT("Loadable segment of size 0x%08x copied from vaddr 0x%08x at 0x%08x\n",
+ cr_pht->p_filesz,
+ cr_pht->p_vaddr,
+ (Elf32_Addr)module_get_absolute(cr_pht->p_vaddr, module));
+ }
+ }
+
+ // Setup dynamic segment location
+ module->dyn_table = module_get_absolute(dyn_addr, module);
+
+ DBG_PRINT("Base address: 0x%08x, aligned at 0x%08x\n", module->base_addr,
+ max_align);
+ DBG_PRINT("Module size: 0x%08x\n", module->module_size);
+
+out:
+ // Free up allocated memory
+ if (pht != NULL)
+ free(pht);
+
+ return res;
+}
+
+
+static int prepare_dynlinking(struct elf_module *module) {
+ Elf32_Dyn *dyn_entry = module->dyn_table;
+
+ while (dyn_entry->d_tag != DT_NULL) {
+ switch (dyn_entry->d_tag) {
+ case DT_NEEDED:
+ // TODO: Manage dependencies here
+ break;
+ case DT_HASH:
+ module->hash_table =
+ (Elf32_Word*)module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+ case DT_GNU_HASH:
+ module->ghash_table =
+ (Elf32_Word*)module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+ case DT_STRTAB:
+ module->str_table =
+ (char*)module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+ case DT_SYMTAB:
+ module->sym_table =
+ module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+ case DT_STRSZ:
+ module->strtable_size = dyn_entry->d_un.d_val;
+ break;
+ case DT_SYMENT:
+ module->syment_size = dyn_entry->d_un.d_val;
+ break;
+ case DT_PLTGOT: // The first entry in the GOT
+ module->got = module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+ }
+
+ dyn_entry++;
+ }
+
+ // Now compute the number of symbols in the symbol table
+ if (module->ghash_table != NULL) {
+ module->symtable_size = module->ghash_table[1];
+ } else {
+ module->symtable_size = module->hash_table[1];
+ }
+
+ return 0;
+}
+
+
+static int perform_relocation(struct elf_module *module, Elf32_Rel *rel) {
+ Elf32_Word *dest = module_get_absolute(rel->r_offset, module);
+
+ // The symbol reference index
+ Elf32_Word sym = ELF32_R_SYM(rel->r_info);
+ unsigned char type = ELF32_R_TYPE(rel->r_info);
+
+ // The symbol definition (if applicable)
+ Elf32_Sym *sym_def = NULL;
+ struct elf_module *sym_module = NULL;
+ Elf32_Addr sym_addr = 0x0;
+
+ if (sym > 0) {
+ // Find out details about the symbol
+
+ // The symbol reference
+ Elf32_Sym *sym_ref =
+ (Elf32_Sym*)(module->sym_table + sym * module->syment_size);
+
+ // The symbol definition
+ sym_def =
+ global_find_symbol(module->str_table + sym_ref->st_name,
+ &sym_module);
+
+ if (sym_def == NULL) {
+ // This should never happen
+ DBG_PRINT("Cannot perform relocation for symbol %s\n",
+ module->str_table + sym_ref->st_name);
+
+ return -1;
+ }
+
+ // Compute the absolute symbol virtual address
+ sym_addr = (Elf32_Addr)module_get_absolute(sym_def->st_value, sym_module);
+
+ if (sym_module != module) {
+ // Create a dependency
+ enforce_dependency(sym_module, module);
+ }
+ }
+
+ switch (type) {
+ case R_386_NONE:
+ // Do nothing
+ break;
+ case R_386_32:
+ *dest += sym_addr;
+ break;
+ case R_386_PC32:
+ *dest += sym_addr - (Elf32_Addr)dest;
+ break;
+ case R_386_COPY:
+ if (sym_addr > 0) {
+ memcpy((void*)dest, (void*)sym_addr, sym_def->st_size);
+ }
+ break;
+ case R_386_GLOB_DAT:
+ case R_386_JMP_SLOT:
+ // Maybe TODO: Keep track of the GOT entries allocations
+ *dest = sym_addr;
+ break;
+ case R_386_RELATIVE:
+ *dest += module->base_addr;
+ break;
+ default:
+ DBG_PRINT("Relocation type %d not supported\n", type);
+ return -1;
+ }
+
+ return 0;
+}
+
+static int resolve_symbols(struct elf_module *module) {
+ Elf32_Dyn *dyn_entry = module->dyn_table;
+ unsigned int i;
+ int res;
+
+ Elf32_Word plt_rel_size = 0;
+ void *plt_rel = NULL;
+
+ void *rel = NULL;
+ Elf32_Word rel_size = 0;
+ Elf32_Word rel_entry = 0;
+
+ // The current relocation
+ Elf32_Rel *crt_rel;
+
+ while (dyn_entry->d_tag != DT_NULL) {
+ switch(dyn_entry->d_tag) {
+
+ // PLT relocation information
+ case DT_PLTRELSZ:
+ plt_rel_size = dyn_entry->d_un.d_val;
+ break;
+ case DT_PLTREL:
+ if (dyn_entry->d_un.d_val != DT_REL) {
+ DBG_PRINT("Unsupported PLT relocation\n");
+ return -1;
+ }
+ case DT_JMPREL:
+ plt_rel = module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+
+ // Standard relocation information
+ case DT_REL:
+ rel = module_get_absolute(dyn_entry->d_un.d_ptr, module);
+ break;
+ case DT_RELSZ:
+ rel_size = dyn_entry->d_un.d_val;
+ break;
+ case DT_RELENT:
+ rel_entry = dyn_entry->d_un.d_val;
+ break;
+
+ // Module initialization and termination
+ case DT_INIT:
+ // TODO Implement initialization functions
+ break;
+ case DT_FINI:
+ // TODO Implement finalization functions
+ break;
+ }
+
+ dyn_entry++;
+ }
+
+ if (rel_size > 0) {
+ // Process standard relocations
+ for (i = 0; i < rel_size/rel_entry; i++) {
+ crt_rel = (Elf32_Rel*)(rel + i*rel_entry);
+
+ res = perform_relocation(module, crt_rel);
+
+ if (res < 0)
+ return res;
+ }
+
+ }
+
+ if (plt_rel_size > 0) {
+ // TODO: Permit this lazily
+ // Process PLT relocations
+ for (i = 0; i < plt_rel_size/sizeof(Elf32_Rel); i++) {
+ crt_rel = (Elf32_Rel*)(plt_rel + i*sizeof(Elf32_Rel));
+
+ res = perform_relocation(module, crt_rel);
+
+ if (res < 0)
+ return res;
+ }
+ }
+
+ return 0;
+}
+
+
+
+static int extract_operations(struct elf_module *module) {
+ Elf32_Sym *init_sym = module_find_symbol(MODULE_ELF_INIT_PTR, module);
+ Elf32_Sym *exit_sym = module_find_symbol(MODULE_ELF_EXIT_PTR, module);
+ Elf32_Sym *main_sym = module_find_symbol(MODULE_ELF_MAIN_PTR, module);
+
+ if (init_sym == NULL) {
+ DBG_PRINT("Cannot find initialization routine pointer.\n");
+ return -1;
+ }
+ if (exit_sym == NULL) {
+ DBG_PRINT("Cannot find exit routine pointer.\n");
+ return -1;
+ }
+ if (main_sym == NULL) {
+ DBG_PRINT("Cannot find main routine pointer.\n");
+ return -1;
+ }
+
+ module->init_func = (module_init_t*)module_get_absolute(
+ init_sym->st_value, module);
+ if (*(module->init_func) == NULL) {
+ module->init_func = NULL;
+ }
+
+ module->exit_func = (module_exit_t*)module_get_absolute(
+ exit_sym->st_value, module);
+ if (*(module->exit_func) == NULL) {
+ module->exit_func = NULL;
+ }
+
+ module->main_func = (module_main_t*)module_get_absolute(
+ main_sym->st_value, module);
+ if (*(module->main_func) == NULL) {
+ module->main_func = NULL;
+ }
+
+ return 0;
+}
+
+// Loads the module into the system
+int module_load(struct elf_module *module) {
+ int res;
+ Elf32_Ehdr elf_hdr;
+
+ // Do not allow duplicate modules
+ if (module_find(module->name) != NULL) {
+ DBG_PRINT("Module already loaded.\n");
+ return -1;
+ }
+
+ // Get a mapping/copy of the ELF file in memory
+ res = image_load(module);
+
+ if (res < 0) {
+ return res;
+ }
+
+ // The module is a fully featured dynamic library
+ module->shallow = 0;
+
+ CHECKED(res, image_read(&elf_hdr, sizeof(Elf32_Ehdr), module), error);
+
+ // Checking the header signature and members
+ CHECKED(res, check_header(&elf_hdr), error);
+
+ // Load the segments in the memory
+ CHECKED(res, load_segments(module, &elf_hdr), error);
+ // Obtain dynamic linking information
+ CHECKED(res, prepare_dynlinking(module), error);
+
+ // Check the symbols for duplicates / missing definitions
+ CHECKED(res, check_symbols(module), error);
+
+ // Obtain constructors and destructors
+ CHECKED(res, extract_operations(module), error);
+
+ // Add the module at the beginning of the module list
+ list_add(&module->list, &modules_head);
+
+ // Perform the relocations
+ resolve_symbols(module);
+
+
+
+ // The file image is no longer needed
+ image_unload(module);
+
+ DBG_PRINT("MODULE %s LOADED SUCCESSFULLY (init@0x%08X, exit@0x%08X)\n",
+ module->name, *(module->init_func), *(module->exit_func));
+
+ return 0;
+
+error:
+ // Remove the module from the module list (if applicable)
+ list_del_init(&module->list);
+
+ if (module->module_addr != NULL) {
+ elf_free(module->module_addr);
+ module->module_addr = NULL;
+ }
+
+ image_unload(module);
+
+ return res;
+}