relocs.c

linux内核源码

		if (fread(symtab[i], 1, shdr[i].sh_size, fp) != shdr[i].sh_size) {
			die("Cannot read symbol table: %s\n",
				strerror(errno));
		}
		for(j = 0; j < shdr[i].sh_size/sizeof(symtab[i][0]); j++) {
			symtab[i][j].st_name  = elf32_to_cpu(symtab[i][j].st_name);
			symtab[i][j].st_value = elf32_to_cpu(symtab[i][j].st_value);
			symtab[i][j].st_size  = elf32_to_cpu(symtab[i][j].st_size);
			symtab[i][j].st_shndx = elf16_to_cpu(symtab[i][j].st_shndx);
		}
	}
}


static void read_relocs(FILE *fp)
{
	int i,j;
	for(i = 0; i < ehdr.e_shnum; i++) {
		if (shdr[i].sh_type != SHT_REL) {
			continue;
		}
		reltab[i] = malloc(shdr[i].sh_size);
		if (!reltab[i]) {
			die("malloc of %d bytes for relocs failed\n",
				shdr[i].sh_size);
		}
		if (fseek(fp, shdr[i].sh_offset, SEEK_SET) < 0) {
			die("Seek to %d failed: %s\n",
				shdr[i].sh_offset, strerror(errno));
		}
		if (fread(reltab[i], 1, shdr[i].sh_size, fp) != shdr[i].sh_size) {
			die("Cannot read symbol table: %s\n",
				strerror(errno));
		}
		for(j = 0; j < shdr[i].sh_size/sizeof(reltab[0][0]); j++) {
			reltab[i][j].r_offset = elf32_to_cpu(reltab[i][j].r_offset);
			reltab[i][j].r_info   = elf32_to_cpu(reltab[i][j].r_info);
		}
	}
}


static void print_absolute_symbols(void)
{
	int i;
	printf("Absolute symbols\n");
	printf(" Num:    Value Size  Type       Bind        Visibility  Name\n");
	for(i = 0; i < ehdr.e_shnum; i++) {
		char *sym_strtab;
		Elf32_Sym *sh_symtab;
		int j;
		if (shdr[i].sh_type != SHT_SYMTAB) {
			continue;
		}
		sh_symtab = symtab[i];
		sym_strtab = strtab[shdr[i].sh_link];
		for(j = 0; j < shdr[i].sh_size/sizeof(symtab[0][0]); j++) {
			Elf32_Sym *sym;
			const char *name;
			sym = &symtab[i][j];
			name = sym_name(sym_strtab, sym);
			if (sym->st_shndx != SHN_ABS) {
				continue;
			}
			printf("%5d %08x %5d %10s %10s %12s %s\n",
				j, sym->st_value, sym->st_size,
				sym_type(ELF32_ST_TYPE(sym->st_info)),
				sym_bind(ELF32_ST_BIND(sym->st_info)),
				sym_visibility(ELF32_ST_VISIBILITY(sym->st_other)),
				name);
		}
	}
	printf("\n");
}

static void print_absolute_relocs(void)
{
	int i, printed = 0;

	for(i = 0; i < ehdr.e_shnum; i++) {
		char *sym_strtab;
		Elf32_Sym *sh_symtab;
		unsigned sec_applies, sec_symtab;
		int j;
		if (shdr[i].sh_type != SHT_REL) {
			continue;
		}
		sec_symtab  = shdr[i].sh_link;
		sec_applies = shdr[i].sh_info;
		if (!(shdr[sec_applies].sh_flags & SHF_ALLOC)) {
			continue;
		}
		sh_symtab = symtab[sec_symtab];
		sym_strtab = strtab[shdr[sec_symtab].sh_link];
		for(j = 0; j < shdr[i].sh_size/sizeof(reltab[0][0]); j++) {
			Elf32_Rel *rel;
			Elf32_Sym *sym;
			const char *name;
			rel = &reltab[i][j];
			sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
			name = sym_name(sym_strtab, sym);
			if (sym->st_shndx != SHN_ABS) {
				continue;
			}

			/* Absolute symbols are not relocated if bzImage is
			 * loaded at a non-compiled address. Display a warning
			 * to user at compile time about the absolute
			 * relocations present.
			 *
			 * User need to audit the code to make sure
			 * some symbols which should have been section
			 * relative have not become absolute because of some
			 * linker optimization or wrong programming usage.
			 *
			 * Before warning check if this absolute symbol
			 * relocation is harmless.
			 */
			if (is_safe_abs_reloc(name))
				continue;

			if (!printed) {
				printf("WARNING: Absolute relocations"
					" present\n");
				printf("Offset     Info     Type     Sym.Value "
					"Sym.Name\n");
				printed = 1;
			}

			printf("%08x %08x %10s %08x  %s\n",
				rel->r_offset,
				rel->r_info,
				rel_type(ELF32_R_TYPE(rel->r_info)),
				sym->st_value,
				name);
		}
	}

	if (printed)
		printf("\n");
}

static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
{
	int i;
	/* Walk through the relocations */
	for(i = 0; i < ehdr.e_shnum; i++) {
		char *sym_strtab;
		Elf32_Sym *sh_symtab;
		unsigned sec_applies, sec_symtab;
		int j;
		if (shdr[i].sh_type != SHT_REL) {
			continue;
		}
		sec_symtab  = shdr[i].sh_link;
		sec_applies = shdr[i].sh_info;
		if (!(shdr[sec_applies].sh_flags & SHF_ALLOC)) {
			continue;
		}
		sh_symtab = symtab[sec_symtab];
		sym_strtab = strtab[shdr[sec_symtab].sh_link];
		for(j = 0; j < shdr[i].sh_size/sizeof(reltab[0][0]); j++) {
			Elf32_Rel *rel;
			Elf32_Sym *sym;
			unsigned r_type;
			rel = &reltab[i][j];
			sym = &sh_symtab[ELF32_R_SYM(rel->r_info)];
			r_type = ELF32_R_TYPE(rel->r_info);
			/* Don't visit relocations to absolute symbols */
			if (sym->st_shndx == SHN_ABS) {
				continue;
			}
			if (r_type == R_386_PC32) {
				/* PC relative relocations don't need to be adjusted */
			}
			else if (r_type == R_386_32) {
				/* Visit relocations that need to be adjusted */
				visit(rel, sym);
			}
			else {
				die("Unsupported relocation type: %d\n", r_type);
			}
		}
	}
}

static void count_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
{
	reloc_count += 1;
}

static void collect_reloc(Elf32_Rel *rel, Elf32_Sym *sym)
{
	/* Remember the address that needs to be adjusted. */
	relocs[reloc_idx++] = rel->r_offset;
}

static int cmp_relocs(const void *va, const void *vb)
{
	const unsigned long *a, *b;
	a = va; b = vb;
	return (*a == *b)? 0 : (*a > *b)? 1 : -1;
}

static void emit_relocs(int as_text)
{
	int i;
	/* Count how many relocations I have and allocate space for them. */
	reloc_count = 0;
	walk_relocs(count_reloc);
	relocs = malloc(reloc_count * sizeof(relocs[0]));
	if (!relocs) {
		die("malloc of %d entries for relocs failed\n",
			reloc_count);
	}
	/* Collect up the relocations */
	reloc_idx = 0;
	walk_relocs(collect_reloc);

	/* Order the relocations for more efficient processing */
	qsort(relocs, reloc_count, sizeof(relocs[0]), cmp_relocs);

	/* Print the relocations */
	if (as_text) {
		/* Print the relocations in a form suitable that
		 * gas will like.
		 */
		printf(".section \".data.reloc\",\"a\"\n");
		printf(".balign 4\n");
		for(i = 0; i < reloc_count; i++) {
			printf("\t .long 0x%08lx\n", relocs[i]);
		}
		printf("\n");
	}
	else {
		unsigned char buf[4];
		buf[0] = buf[1] = buf[2] = buf[3] = 0;
		/* Print a stop */
		printf("%c%c%c%c", buf[0], buf[1], buf[2], buf[3]);
		/* Now print each relocation */
		for(i = 0; i < reloc_count; i++) {
			buf[0] = (relocs[i] >>  0) & 0xff;
			buf[1] = (relocs[i] >>  8) & 0xff;
			buf[2] = (relocs[i] >> 16) & 0xff;
			buf[3] = (relocs[i] >> 24) & 0xff;
			printf("%c%c%c%c", buf[0], buf[1], buf[2], buf[3]);
		}
	}
}

static void usage(void)
{
	die("relocs [--abs-syms |--abs-relocs | --text] vmlinux\n");
}

int main(int argc, char **argv)
{
	int show_absolute_syms, show_absolute_relocs;
	int as_text;
	const char *fname;
	FILE *fp;
	int i;

	show_absolute_syms = 0;
	show_absolute_relocs = 0;
	as_text = 0;
	fname = NULL;
	for(i = 1; i < argc; i++) {
		char *arg = argv[i];
		if (*arg == '-') {
			if (strcmp(argv[1], "--abs-syms") == 0) {
				show_absolute_syms = 1;
				continue;
			}

			if (strcmp(argv[1], "--abs-relocs") == 0) {
				show_absolute_relocs = 1;
				continue;
			}
			else if (strcmp(argv[1], "--text") == 0) {
				as_text = 1;
				continue;
			}
		}
		else if (!fname) {
			fname = arg;
			continue;
		}
		usage();
	}
	if (!fname) {
		usage();
	}
	fp = fopen(fname, "r");
	if (!fp) {
		die("Cannot open %s: %s\n",
			fname, strerror(errno));
	}
	read_ehdr(fp);
	read_shdrs(fp);
	read_strtabs(fp);
	read_symtabs(fp);
	read_relocs(fp);
	if (show_absolute_syms) {
		print_absolute_symbols();
		return 0;
	}
	if (show_absolute_relocs) {
		print_absolute_relocs();
		return 0;
	}
	emit_relocs(as_text);
	return 0;
}