make _start global in runtime

lib/runtime.asm

@@ -6,6 +6,7 @@
 #
 
 .extern main
+.globl _start
 
 .stack
 .align 2

mld/link.c

@@ -44,7 +44,7 @@ static int load_objects(struct linker *linker)
 
 		// load obj file
 		linker->obj_len++;
-		if (object_load(obj, path))
+		if (object_load(obj, path, i+1))
 			return M_ERROR;
 skip_obj:
 	}
@@ -55,7 +55,7 @@ skip_obj:
 
 		char *path = _STR(PREFIX) "/lib/mips/runtime.o";
 		struct object *obj = &linker->objects[linker->obj_len++];
-		if (object_load(obj, path))
+		if (object_load(obj, path, 0))
 			return M_ERROR;
 
 		#undef _STR
@@ -208,7 +208,7 @@ static int relocate_symbol(struct linker *linker, struct object *obj,
 	new.st_shndx = B16(new_shndx);
 	new.st_size = 0;
 
-	if (symtab_get(&linker->symtab, NULL, name) == M_SUCCESS) {
+	if (symtab_get(&linker->symtab, NULL, name, obj->index) == M_SUCCESS) {
 		ERROR("cannot link doubly defiend symbol '%s'", name);
 		return M_ERROR;
 	}
@@ -216,6 +216,9 @@ static int relocate_symbol(struct linker *linker, struct object *obj,
 	if (symtab_push(&linker->symtab, &new))
 		return M_ERROR;
 
+	if (symtab_map_push(&linker->symtab_map, obj))
+		return M_ERROR;
+
 	return M_SUCCESS;
 }
 
@@ -380,12 +383,12 @@ static int relocate_instruction_rela(struct linker *linker,
 	/// of this relocation in that segment part
 	uint32_t off = B32(rel->r_offset);
 	if (off > seg->size) {
-		ERROR("relocation in segment '%s' out of bounds", seg->name);
+		ERROR("invalid relocation in '%s'", seg->obj->name);
 		return M_ERROR;
 	}
 
 	if (B32(rel->r_info) == 0) {
-		WARNING("skiping empty relocation entry");
+		WARNING("skiping empty relocation entry in '%s'", seg->name);
 		return M_SUCCESS;
 	}
 
@@ -397,22 +400,21 @@ static int relocate_instruction_rela(struct linker *linker,
 	/// read the symbol from the relocation
 	struct symbol_table *symtab = seg->reltab.symtab;
 	if (idx >= symtab->len) {
-		ERROR("relocation in segment '%s', symbol index [%d] out of "
+		ERROR("invalid relocation in '%s'", seg->obj->name);
-			"bounds", seg->name, idx);
 		return M_ERROR;
 	}
 	Elf32_Sym *sym = &symtab->syms[idx];
 
 	char const *sym_name = symtab->strtab->data + B32(sym->st_name);
 	if (B32(sym->st_name) >= symtab->strtab->len) {
-		ERROR("relocation symbol name out of bounds");
+		ERROR("symbol name out of bounds in '%s'", seg->obj->name);
 		return M_ERROR;
 	}
 
 	// get the new sym for the new vaddr
 	Elf32_Sym *new_sym = NULL;
-	if (symtab_get(&linker->symtab, &new_sym, sym_name)) {
+	if (symtab_get(&linker->symtab, &new_sym, sym_name, seg->obj->index)) {
-		ERROR("relocation symbol not found");
+		ERROR("symbol '%s' undefined", sym_name);
 		return M_ERROR;
 	}
 
@@ -656,7 +658,7 @@ static int link_executable(struct linker *linker)
 	ehdr->e_shstrndx = B16(linker->shstrtab_shidx);
 
 	Elf32_Sym *entry = NULL;
-	if (symtab_get(&linker->symtab, &entry, "_start")) {
+	if (symtab_get(&linker->symtab, &entry, "_start", -1)) {
 		ERROR("undefined symbol _start");
 		return M_ERROR;
 	}
@@ -681,6 +683,7 @@ static int linker_init(struct linker *linker, struct linker_arguments *args)
 	linker->objects = NULL;
 	linker->segments.size = 0;
 	linker->symtab.syms = NULL;
+	linker->symtab_map.meta = NULL;
 	linker->shstrtab.data = NULL;
 	linker->strtab.data = NULL;
 	linker->shdr = NULL;
@@ -693,7 +696,10 @@ static int linker_init(struct linker *linker, struct linker_arguments *args)
 		return M_ERROR;
 	if (symtab_init(&linker->symtab))
 		return M_ERROR;
+	if (symtab_map_init(&linker->symtab_map))
+		return M_ERROR;
 	linker->symtab.strtab = &linker->strtab;
+	linker->symtab.map = &linker->symtab_map;
 	return M_SUCCESS;
 }
 
@@ -712,6 +718,7 @@ static void linker_free(struct linker *linker)
 	strtab_free(&linker->shstrtab);
 	strtab_free(&linker->strtab);
 	symtab_free(&linker->symtab);
+	symtab_map_free(&linker->symtab_map);
 }
 
 int link_files(struct linker_arguments args) {

mld/link.h

@@ -39,6 +39,9 @@
 struct linker;
 struct object;
 struct segment;
+struct string_table;
+struct symbol_table;
+struct symbol_table_mapping;
 
 ///
 /// relocation table
@@ -79,13 +82,35 @@ struct symbol_table {
 	Elf32_Sym *syms;
 	size_t len;
 	size_t size;
+
+	// mapping for global symbol table
+	// can be null
+	// (metadata for each symbol)
+	struct symbol_table_mapping *map;
 };
 
+///
+/// symbol table map
+/// (metadata for each symbol)
+///
+
 int symtab_init(struct symbol_table *symtab);
 void symtab_free(struct symbol_table *symtab);
 
 int symtab_push(struct symbol_table *symtab, const Elf32_Sym *sym);
-int symtab_get(struct symbol_table *symtab, Elf32_Sym **sym, const char *name);
+int symtab_get(struct symbol_table *symtab, Elf32_Sym **sym, const char *name,
+	       int32_t obj_idx);
+
+struct symbol_table_mapping {
+	uint32_t len;
+	uint32_t size;
+	struct object **meta;
+};
+
+int symtab_map_push(struct symbol_table_mapping *symtabm, struct object *seg);
+
+int symtab_map_init(struct symbol_table_mapping *symtabm);
+void symtab_map_free(struct symbol_table_mapping *symtabm);
 
 ///
 /// segment
@@ -211,7 +236,7 @@ struct object {
 	struct symbol_table *symtabs;
 };
 
-int object_load(struct object *object, char *path);
+int object_load(struct object *object, char *path, uint32_t index);
 
 void object_free(struct object *object);
 
@@ -235,6 +260,7 @@ struct linker {
 	struct string_table shstrtab;
 	struct string_table strtab;
 	struct symbol_table symtab;
+	struct symbol_table_mapping symtab_map;
 
 	// output elf
 	Elf32_Ehdr ehdr;

mld/obj.c

@@ -276,7 +276,7 @@ static int map_file(struct object *obj, char *path)
 	return M_SUCCESS;
 }
 
-int object_load(struct object *object, char *path)
+int object_load(struct object *object, char *path, uint32_t index)
 {
 	current_file = path;
 
@@ -286,6 +286,7 @@ int object_load(struct object *object, char *path)
 	object->strtabs = NULL;
 	object->mapped = NULL;
 	object->name = path;
+	object->index = index;
 
 	/** load the file */
 	if (map_file(object, path))

mld/symtab.c

@@ -1,5 +1,6 @@
 #include <elf.h>
 #include <merror.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <melf.h>
 
@@ -19,6 +20,7 @@ int symtab_init(struct symbol_table *symtab)
 	}
 
 	symtab->syms[0] = (Elf32_Sym){0};
+	symtab->map = NULL;
 
 	return M_SUCCESS;
 }
@@ -45,16 +47,69 @@ int symtab_push(struct symbol_table *symtab, const Elf32_Sym *sym)
 	return M_SUCCESS;
 }
 
-int symtab_get(struct symbol_table *symtab, Elf32_Sym **res, const char *name)
+int symtab_get(struct symbol_table *symtab, Elf32_Sym **res, const char *name,
+	       int32_t obj_idx)
 {
 	for (size_t i = 0; i < symtab->len; i++) {
 		Elf32_Sym *sym = &symtab->syms[i];
 		const char *symname = symtab->strtab->data + B32(sym->st_name);
-		if (strcmp(name, symname) == 0) {
+		if (strcmp(name, symname) != 0)
+			continue;
+
+		// only allow retrevial of local variables from the
+		// same object
+		if (sym->st_info >> 4 != STB_GLOBAL && symtab->map != NULL &&
+			obj_idx >= 0) {
+			struct object *obj = symtab->map->meta[i];
+			if (obj->index != (uint32_t)obj_idx)
+				continue;
+		} else if (obj_idx < 0 && sym->st_info >> 4 != STB_GLOBAL) {
+			// when obj_idx is -1, we only want to reutrn
+			// global symbols
+			continue;
+		}
+
 		if (res != NULL)
 			*res = sym;
 		return M_SUCCESS;
 	}
-	}
 	return M_ERROR;
 }
+
+int symtab_map_push(struct symbol_table_mapping *symtabm, struct object *meta)
+{
+	if (symtabm->len >= symtabm->size) {
+		uint32_t size = symtabm->size * 2;
+		void *new = realloc(symtabm->meta,
+		      sizeof(struct object *) * size);
+		if (new == NULL) {
+			PERROR("cannot realloc");
+			return M_ERROR;
+		}
+		symtabm->size = size;
+		symtabm->meta = new;
+	}
+
+	symtabm->meta[symtabm->len++] = meta;
+	return M_SUCCESS;
+}
+
+int symtab_map_init(struct symbol_table_mapping *symtabm)
+{
+	symtabm->len = 0;
+	symtabm->size = SYMTAB_INIT_LEN;
+	symtabm->meta = malloc(sizeof(struct object *) * symtabm->size);
+
+	if (symtabm->meta == NULL) {
+		PERROR("cannot alloc");
+		return M_ERROR;
+	}
+
+	return M_SUCCESS;
+}
+
+
+void symtab_map_free(struct symbol_table_mapping *symtabm)
+{
+	free(symtabm->meta);
+}