MIPS: tools: Add relocs tool

This tool is based on the x86/boot/tools/relocs tool.

It parses the relocations present in the vmlinux elf file, building a
table of relocations that will be necessary to run the kernel from an
address other than its link address. This table is inserted into the
vmlinux elf, in the .data.relocs section. The table is subsequently used
by the code in arch/mips/kernel/relocate.c (added later) to relocate the
kernel.

The tool, by default, also marks all relocation sections as 0 length.
This is due to objcopy currently being unable to handle copying the
relocations between 64 and 32 bit elf files as is done when building a
64 bit kernel.
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: kernel-hardening@lists.openwall.com
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/12981/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/boot/tools/Makefile

+
+hostprogs-y	+= relocs
+relocs-objs	+= relocs_32.o
+relocs-objs	+= relocs_64.o
+relocs-objs	+= relocs_main.o
+PHONY += relocs
+relocs: $(obj)/relocs
+	@:

arch/mips/boot/tools/relocs.c

+/* This is included from relocs_32/64.c */
+
+#define ElfW(type)		_ElfW(ELF_BITS, type)
+#define _ElfW(bits, type)	__ElfW(bits, type)
+#define __ElfW(bits, type)	Elf##bits##_##type
+
+#define Elf_Addr		ElfW(Addr)
+#define Elf_Ehdr		ElfW(Ehdr)
+#define Elf_Phdr		ElfW(Phdr)
+#define Elf_Shdr		ElfW(Shdr)
+#define Elf_Sym			ElfW(Sym)
+
+static Elf_Ehdr ehdr;
+
+struct relocs {
+	uint32_t	*offset;
+	unsigned long	count;
+	unsigned long	size;
+};
+
+static struct relocs relocs;
+
+struct section {
+	Elf_Shdr       shdr;
+	struct section *link;
+	Elf_Sym        *symtab;
+	Elf_Rel        *reltab;
+	char           *strtab;
+	long           shdr_offset;
+};
+static struct section *secs;
+
+static const char * const regex_sym_kernel = {
+/* Symbols matching these regex's should never be relocated */
+	"^(__crc_)",
+};
+
+static regex_t sym_regex_c;
+
+static int regex_skip_reloc(const char *sym_name)
+{
+	return !regexec(&sym_regex_c, sym_name, 0, NULL, 0);
+}
+
+static void regex_init(void)
+{
+	char errbuf[128];
+	int err;
+
+	err = regcomp(&sym_regex_c, regex_sym_kernel,
+			REG_EXTENDED|REG_NOSUB);
+
+	if (err) {
+		regerror(err, &sym_regex_c, errbuf, sizeof(errbuf));
+		die("%s", errbuf);
+	}
+}
+
+static const char *rel_type(unsigned type)
+{
+	static const char * const type_name[] = {
+#define REL_TYPE(X)[X] = #X
+		REL_TYPE(R_MIPS_NONE),
+		REL_TYPE(R_MIPS_16),
+		REL_TYPE(R_MIPS_32),
+		REL_TYPE(R_MIPS_REL32),
+		REL_TYPE(R_MIPS_26),
+		REL_TYPE(R_MIPS_HI16),
+		REL_TYPE(R_MIPS_LO16),
+		REL_TYPE(R_MIPS_GPREL16),
+		REL_TYPE(R_MIPS_LITERAL),
+		REL_TYPE(R_MIPS_GOT16),
+		REL_TYPE(R_MIPS_PC16),
+		REL_TYPE(R_MIPS_CALL16),
+		REL_TYPE(R_MIPS_GPREL32),
+		REL_TYPE(R_MIPS_64),
+		REL_TYPE(R_MIPS_HIGHER),
+		REL_TYPE(R_MIPS_HIGHEST),
+		REL_TYPE(R_MIPS_PC21_S2),
+		REL_TYPE(R_MIPS_PC26_S2),
+#undef REL_TYPE
+	};
+	const char *name = "unknown type rel type name";
+
+	if (type < ARRAY_SIZE(type_name) && type_name[type])
+		name = type_name[type];
+	return name;
+}
+
+static const char *sec_name(unsigned shndx)
+{
+	const char *sec_strtab;
+	const char *name;
+
+	sec_strtab = secs[ehdr.e_shstrndx].strtab;
+	if (shndx < ehdr.e_shnum)
+		name = sec_strtab + secs[shndx].shdr.sh_name;
+	else if (shndx == SHN_ABS)
+		name = "ABSOLUTE";
+	else if (shndx == SHN_COMMON)
+		name = "COMMON";
+	else
+		name = "<noname>";
+	return name;
+}
+
+static struct section *sec_lookup(const char *secname)
+{
+	int i;
+
+	for (i = 0; i < ehdr.e_shnum; i++)
+		if (strcmp(secname, sec_name(i)) == 0)
+			return &secs[i];
+
+	return NULL;
+}
+
+static const char *sym_name(const char *sym_strtab, Elf_Sym *sym)
+{
+	const char *name;
+
+	if (sym->st_name)
+		name = sym_strtab + sym->st_name;
+	else
+		name = sec_name(sym->st_shndx);
+	return name;
+}
+
+#if BYTE_ORDER == LITTLE_ENDIAN
+#define le16_to_cpu(val) (val)
+#define le32_to_cpu(val) (val)
+#define le64_to_cpu(val) (val)
+#define be16_to_cpu(val) bswap_16(val)
+#define be32_to_cpu(val) bswap_32(val)
+#define be64_to_cpu(val) bswap_64(val)
+
+#define cpu_to_le16(val) (val)
+#define cpu_to_le32(val) (val)
+#define cpu_to_le64(val) (val)
+#define cpu_to_be16(val) bswap_16(val)
+#define cpu_to_be32(val) bswap_32(val)
+#define cpu_to_be64(val) bswap_64(val)
+#endif
+#if BYTE_ORDER == BIG_ENDIAN
+#define le16_to_cpu(val) bswap_16(val)
+#define le32_to_cpu(val) bswap_32(val)
+#define le64_to_cpu(val) bswap_64(val)
+#define be16_to_cpu(val) (val)
+#define be32_to_cpu(val) (val)
+#define be64_to_cpu(val) (val)
+
+#define cpu_to_le16(val) bswap_16(val)
+#define cpu_to_le32(val) bswap_32(val)
+#define cpu_to_le64(val) bswap_64(val)
+#define cpu_to_be16(val) (val)
+#define cpu_to_be32(val) (val)
+#define cpu_to_be64(val) (val)
+#endif
+
+static uint16_t elf16_to_cpu(uint16_t val)
+{
+	if (ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
+		return le16_to_cpu(val);
+	else
+		return be16_to_cpu(val);
+}
+
+static uint32_t elf32_to_cpu(uint32_t val)
+{
+	if (ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
+		return le32_to_cpu(val);
+	else
+		return be32_to_cpu(val);
+}
+
+static uint32_t cpu_to_elf32(uint32_t val)
+{
+	if (ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
+		return cpu_to_le32(val);
+	else
+		return cpu_to_be32(val);
+}
+
+#define elf_half_to_cpu(x)	elf16_to_cpu(x)
+#define elf_word_to_cpu(x)	elf32_to_cpu(x)
+
+#if ELF_BITS == 64
+static uint64_t elf64_to_cpu(uint64_t val)
+{
+	if (ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
+		return le64_to_cpu(val);
+	else
+		return be64_to_cpu(val);
+}
+#define elf_addr_to_cpu(x)	elf64_to_cpu(x)
+#define elf_off_to_cpu(x)	elf64_to_cpu(x)
+#define elf_xword_to_cpu(x)	elf64_to_cpu(x)
+#else
+#define elf_addr_to_cpu(x)	elf32_to_cpu(x)
+#define elf_off_to_cpu(x)	elf32_to_cpu(x)
+#define elf_xword_to_cpu(x)	elf32_to_cpu(x)
+#endif
+
+static void read_ehdr(FILE *fp)
+{
+	if (fread(&ehdr, sizeof(ehdr), 1, fp) != 1)
+		die("Cannot read ELF header: %s\n", strerror(errno));
+
+	if (memcmp(ehdr.e_ident, ELFMAG, SELFMAG) != 0)
+		die("No ELF magic\n");
+
+	if (ehdr.e_ident[EI_CLASS] != ELF_CLASS)
+		die("Not a %d bit executable\n", ELF_BITS);
+
+	if ((ehdr.e_ident[EI_DATA] != ELFDATA2LSB) &&
+	    (ehdr.e_ident[EI_DATA] != ELFDATA2MSB))
+		die("Unknown ELF Endianness\n");
+
+	if (ehdr.e_ident[EI_VERSION] != EV_CURRENT)
+		die("Unknown ELF version\n");
+
+	/* Convert the fields to native endian */
+	ehdr.e_type      = elf_half_to_cpu(ehdr.e_type);
+	ehdr.e_machine   = elf_half_to_cpu(ehdr.e_machine);
+	ehdr.e_version   = elf_word_to_cpu(ehdr.e_version);
+	ehdr.e_entry     = elf_addr_to_cpu(ehdr.e_entry);
+	ehdr.e_phoff     = elf_off_to_cpu(ehdr.e_phoff);
+	ehdr.e_shoff     = elf_off_to_cpu(ehdr.e_shoff);
+	ehdr.e_flags     = elf_word_to_cpu(ehdr.e_flags);
+	ehdr.e_ehsize    = elf_half_to_cpu(ehdr.e_ehsize);
+	ehdr.e_phentsize = elf_half_to_cpu(ehdr.e_phentsize);
+	ehdr.e_phnum     = elf_half_to_cpu(ehdr.e_phnum);
+	ehdr.e_shentsize = elf_half_to_cpu(ehdr.e_shentsize);
+	ehdr.e_shnum     = elf_half_to_cpu(ehdr.e_shnum);
+	ehdr.e_shstrndx  = elf_half_to_cpu(ehdr.e_shstrndx);
+
+	if ((ehdr.e_type != ET_EXEC) && (ehdr.e_type != ET_DYN))
+		die("Unsupported ELF header type\n");
+
+	if (ehdr.e_machine != ELF_MACHINE)
+		die("Not for %s\n", ELF_MACHINE_NAME);
+
+	if (ehdr.e_version != EV_CURRENT)
+		die("Unknown ELF version\n");
+
+	if (ehdr.e_ehsize != sizeof(Elf_Ehdr))
+		die("Bad Elf header size\n");
+
+	if (ehdr.e_phentsize != sizeof(Elf_Phdr))
+		die("Bad program header entry\n");
+
+	if (ehdr.e_shentsize != sizeof(Elf_Shdr))
+		die("Bad section header entry\n");
+
+	if (ehdr.e_shstrndx >= ehdr.e_shnum)
+		die("String table index out of bounds\n");
+}
+
+static void read_shdrs(FILE *fp)
+{
+	int i;
+	Elf_Shdr shdr;
+
+	secs = calloc(ehdr.e_shnum, sizeof(struct section));
+	if (!secs)
+		die("Unable to allocate %d section headers\n", ehdr.e_shnum);
+
+	if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0)
+		die("Seek to %d failed: %s\n", ehdr.e_shoff, strerror(errno));
+
+	for (i = 0; i < ehdr.e_shnum; i++) {
+		struct section *sec = &secs[i];
+
+		sec->shdr_offset = ftell(fp);
+		if (fread(&shdr, sizeof(shdr), 1, fp) != 1)
+			die("Cannot read ELF section headers %d/%d: %s\n",
+			    i, ehdr.e_shnum, strerror(errno));
+		sec->shdr.sh_name      = elf_word_to_cpu(shdr.sh_name);
+		sec->shdr.sh_type      = elf_word_to_cpu(shdr.sh_type);
+		sec->shdr.sh_flags     = elf_xword_to_cpu(shdr.sh_flags);
+		sec->shdr.sh_addr      = elf_addr_to_cpu(shdr.sh_addr);
+		sec->shdr.sh_offset    = elf_off_to_cpu(shdr.sh_offset);
+		sec->shdr.sh_size      = elf_xword_to_cpu(shdr.sh_size);
+		sec->shdr.sh_link      = elf_word_to_cpu(shdr.sh_link);
+		sec->shdr.sh_info      = elf_word_to_cpu(shdr.sh_info);
+		sec->shdr.sh_addralign = elf_xword_to_cpu(shdr.sh_addralign);
+		sec->shdr.sh_entsize   = elf_xword_to_cpu(shdr.sh_entsize);
+		if (sec->shdr.sh_link < ehdr.e_shnum)
+			sec->link = &secs[sec->shdr.sh_link];
+	}
+}
+
+static void read_strtabs(FILE *fp)
+{
+	int i;
+
+	for (i = 0; i < ehdr.e_shnum; i++) {
+		struct section *sec = &secs[i];
+
+		if (sec->shdr.sh_type != SHT_STRTAB)
+			continue;
+
+		sec->strtab = malloc(sec->shdr.sh_size);
+		if (!sec->strtab)
+			die("malloc of %d bytes for strtab failed\n",
+			    sec->shdr.sh_size);
+
+		if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0)
+			die("Seek to %d failed: %s\n",
+			    sec->shdr.sh_offset, strerror(errno));
+
+		if (fread(sec->strtab, 1, sec->shdr.sh_size, fp) !=
+		    sec->shdr.sh_size)
+			die("Cannot read symbol table: %s\n", strerror(errno));
+	}
+}
+
+static void read_symtabs(FILE *fp)
+{
+	int i, j;
+
+	for (i = 0; i < ehdr.e_shnum; i++) {
+		struct section *sec = &secs[i];
+		if (sec->shdr.sh_type != SHT_SYMTAB)
+			continue;
+
+		sec->symtab = malloc(sec->shdr.sh_size);
+		if (!sec->symtab)
+			die("malloc of %d bytes for symtab failed\n",
+			    sec->shdr.sh_size);
+
+		if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0)
+			die("Seek to %d failed: %s\n",
+			    sec->shdr.sh_offset, strerror(errno));
+
+		if (fread(sec->symtab, 1, sec->shdr.sh_size, fp) !=
+		    sec->shdr.sh_size)
+			die("Cannot read symbol table: %s\n", strerror(errno));
+
+		for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Sym); j++) {
+			Elf_Sym *sym = &sec->symtab[j];
+
+			sym->st_name  = elf_word_to_cpu(sym->st_name);
+			sym->st_value = elf_addr_to_cpu(sym->st_value);
+			sym->st_size  = elf_xword_to_cpu(sym->st_size);
+			sym->st_shndx = elf_half_to_cpu(sym->st_shndx);
+		}
+	}
+}
+
+static void read_relocs(FILE *fp)
+{
+	static unsigned long base = 0;
+	int i, j;
+
+	if (!base) {
+		struct section *sec = sec_lookup(".text");
+
+		if (!sec)
+			die("Could not find .text section\n");
+
+		base = sec->shdr.sh_addr;
+	}
+
+	for (i = 0; i < ehdr.e_shnum; i++) {
+		struct section *sec = &secs[i];
+
+		if (sec->shdr.sh_type != SHT_REL_TYPE)
+			continue;
+
+		sec->reltab = malloc(sec->shdr.sh_size);
+		if (!sec->reltab)
+			die("malloc of %d bytes for relocs failed\n",
+			    sec->shdr.sh_size);
+
+		if (fseek(fp, sec->shdr.sh_offset, SEEK_SET) < 0)
+			die("Seek to %d failed: %s\n",
+			    sec->shdr.sh_offset, strerror(errno));
+
+		if (fread(sec->reltab, 1, sec->shdr.sh_size, fp) !=
+		    sec->shdr.sh_size)
+			die("Cannot read symbol table: %s\n", strerror(errno));
+
+		for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Rel); j++) {
+			Elf_Rel *rel = &sec->reltab[j];
+
+			rel->r_offset = elf_addr_to_cpu(rel->r_offset);
+			/* Set offset into kernel image */
+			rel->r_offset -= base;
+#if (ELF_BITS == 32)
+			rel->r_info   = elf_xword_to_cpu(rel->r_info);
+#else
+			/* Convert MIPS64 RELA format - only the symbol
+			 * index needs converting to native endianness
+			 */
+			rel->r_info   = rel->r_info;
+			ELF_R_SYM(rel->r_info) = elf32_to_cpu(ELF_R_SYM(rel->r_info));
+#endif
+#if (SHT_REL_TYPE == SHT_RELA)
+			rel->r_addend = elf_xword_to_cpu(rel->r_addend);
+#endif
+		}
+	}
+}
+
+static void remove_relocs(FILE *fp)
+{
+	int i;
+	Elf_Shdr shdr;
+
+	for (i = 0; i < ehdr.e_shnum; i++) {
+		struct section *sec = &secs[i];
+
+		if (sec->shdr.sh_type != SHT_REL_TYPE)
+			continue;
+
+		if (fseek(fp, sec->shdr_offset, SEEK_SET) < 0)
+			die("Seek to %d failed: %s\n",
+			    sec->shdr_offset, strerror(errno));
+
+		if (fread(&shdr, sizeof(shdr), 1, fp) != 1)
+			die("Cannot read ELF section headers %d/%d: %s\n",
+			    i, ehdr.e_shnum, strerror(errno));
+
+		/* Set relocation section size to 0, effectively removing it.
+		 * This is necessary due to lack of support for relocations
+		 * in objcopy when creating 32bit elf from 64bit elf.
+		 */
+		shdr.sh_size = 0;
+
+		if (fseek(fp, sec->shdr_offset, SEEK_SET) < 0)
+			die("Seek to %d failed: %s\n",
+			    sec->shdr_offset, strerror(errno));
+
+		if (fwrite(&shdr, sizeof(shdr), 1, fp) != 1)
+			die("Cannot write ELF section headers %d/%d: %s\n",
+			    i, ehdr.e_shnum, strerror(errno));
+	}
+}
+
+static void add_reloc(struct relocs *r, uint32_t offset, unsigned type)
+{
+	/* Relocation representation in binary table:
+	 * |76543210|76543210|76543210|76543210|
+	 * |  Type  |  offset from _text >> 2  |
+	 */
+	offset >>= 2;
+	if (offset > 0x00FFFFFF)
+		die("Kernel image exceeds maximum size for relocation!\n");
+
+	offset = (offset & 0x00FFFFFF) | ((type & 0xFF) << 24);
+
+	if (r->count == r->size) {
+		unsigned long newsize = r->size + 50000;
+		void *mem = realloc(r->offset, newsize * sizeof(r->offset[0]));
+
+		if (!mem)
+			die("realloc failed\n");
+
+		r->offset = mem;
+		r->size = newsize;
+	}
+	r->offset[r->count++] = offset;
+}
+
+static void walk_relocs(int (*process)(struct section *sec, Elf_Rel *rel,
+			Elf_Sym *sym, const char *symname))
+{
+	int i;
+
+	/* Walk through the relocations */
+	for (i = 0; i < ehdr.e_shnum; i++) {
+		char *sym_strtab;
+		Elf_Sym *sh_symtab;
+		struct section *sec_applies, *sec_symtab;
+		int j;
+		struct section *sec = &secs[i];
+
+		if (sec->shdr.sh_type != SHT_REL_TYPE)
+			continue;
+
+		sec_symtab  = sec->link;
+		sec_applies = &secs[sec->shdr.sh_info];
+		if (!(sec_applies->shdr.sh_flags & SHF_ALLOC))
+			continue;
+
+		sh_symtab = sec_symtab->symtab;
+		sym_strtab = sec_symtab->link->strtab;
+		for (j = 0; j < sec->shdr.sh_size/sizeof(Elf_Rel); j++) {
+			Elf_Rel *rel = &sec->reltab[j];
+			Elf_Sym *sym = &sh_symtab[ELF_R_SYM(rel->r_info)];
+			const char *symname = sym_name(sym_strtab, sym);
+
+			process(sec, rel, sym, symname);
+		}
+	}
+}
+
+static int do_reloc(struct section *sec, Elf_Rel *rel, Elf_Sym *sym,
+		      const char *symname)
+{
+	unsigned r_type = ELF_R_TYPE(rel->r_info);
+	unsigned bind = ELF_ST_BIND(sym->st_info);
+
+	if ((bind == STB_WEAK) && (sym->st_value == 0)) {
+		/* Don't relocate weak symbols without a target */
+		return 0;
+	}
+
+	if (regex_skip_reloc(symname))
+		return 0;
+
+	switch (r_type) {
+	case R_MIPS_NONE:
+	case R_MIPS_REL32:
+	case R_MIPS_PC16:
+	case R_MIPS_PC21_S2:
+	case R_MIPS_PC26_S2:
+		/*
+		 * NONE can be ignored and PC relative relocations don't
+		 * need to be adjusted.
+		 */
+	case R_MIPS_HIGHEST:
+	case R_MIPS_HIGHER:
+		/* We support relocating within the same 4Gb segment only,
+		 * thus leaving the top 32bits unchanged
+		 */
+	case R_MIPS_LO16:
+		/* We support relocating by 64k jumps only
+		 * thus leaving the bottom 16bits unchanged
+		 */
+		break;
+
+	case R_MIPS_64:
+	case R_MIPS_32:
+	case R_MIPS_26:
+	case R_MIPS_HI16:
+		add_reloc(&relocs, rel->r_offset, r_type);
+		break;
+
+	default:
+		die("Unsupported relocation type: %s (%d)\n",
+		    rel_type(r_type), r_type);
+		break;
+	}
+
+	return 0;
+}
+
+static int write_reloc_as_bin(uint32_t v, FILE *f)
+{
+	unsigned char buf[4];
+
+	v = cpu_to_elf32(v);
+
+	memcpy(buf, &v, sizeof(uint32_t));
+	return fwrite(buf, 1, 4, f);
+}
+
+static int write_reloc_as_text(uint32_t v, FILE *f)
+{
+	int res;
+
+	res = fprintf(f, "\t.long 0x%08"PRIx32"\n", v);
+	if (res < 0)
+		return res;
+	else
+		return sizeof(uint32_t);
+}
+
+static void emit_relocs(int as_text, int as_bin, FILE *outf)
+{
+	int i;
+	int (*write_reloc)(uint32_t, FILE *) = write_reloc_as_bin;
+	int size = 0;
+	int size_reserved;
+	struct section *sec_reloc;
+
+	sec_reloc = sec_lookup(".data.reloc");
+	if (!sec_reloc)
+		die("Could not find relocation section\n");
+
+	size_reserved = sec_reloc->shdr.sh_size;
+
+	/* Collect up the relocations */
+	walk_relocs(do_reloc);
+
+	/* 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");
+		/* Output text to stdout */
+		write_reloc = write_reloc_as_text;
+		outf = stdout;
+	} else if (as_bin) {
+		/* Output raw binary to stdout */
+		outf = stdout;
+	} else {
+		/* Seek to offset of the relocation section.
+		* Each relocation is then written into the
+		* vmlinux kernel image.
+		*/
+		if (fseek(outf, sec_reloc->shdr.sh_offset, SEEK_SET) < 0) {
+			die("Seek to %d failed: %s\n",
+				sec_reloc->shdr.sh_offset, strerror(errno));
+		}
+	}
+
+	for (i = 0; i < relocs.count; i++)
+		size += write_reloc(relocs.offset[i], outf);
+
+	/* Print a stop, but only if we've actually written some relocs */
+	if (size)
+		size += write_reloc(0, outf);
+
+	if (size > size_reserved)
+		/* Die, but suggest a value for CONFIG_RELOCATION_TABLE_SIZE
+		 * which will fix this problem and allow a bit of headroom
+		 * if more kernel features are enabled
+		 */
+		die("Relocations overflow available space!\n" \
+		    "Please adjust CONFIG_RELOCATION_TABLE_SIZE " \
+		    "to at least 0x%08x\n", (size + 0x1000) & ~0xFFF);
+}
+
+/*
+ * As an aid to debugging problems with different linkers
+ * print summary information about the relocs.
+ * Since different linkers tend to emit the sections in
+ * different orders we use the section names in the output.
+ */
+static int do_reloc_info(struct section *sec, Elf_Rel *rel, ElfW(Sym) *sym,
+				const char *symname)
+{
+	printf("%16s  0x%08x  %16s  %40s  %16s\n",
+		sec_name(sec->shdr.sh_info),
+		(unsigned int)rel->r_offset,
+		rel_type(ELF_R_TYPE(rel->r_info)),
+		symname,
+		sec_name(sym->st_shndx));
+	return 0;
+}
+
+static void print_reloc_info(void)
+{
+	printf("%16s  %10s  %16s  %40s  %16s\n",
+		"reloc section",
+		"offset",
+		"reloc type",
+		"symbol",
+		"symbol section");
+	walk_relocs(do_reloc_info);
+}
+
+#if ELF_BITS == 64
+# define process process_64
+#else
+# define process process_32
+#endif
+
+void process(FILE *fp, int as_text, int as_bin,
+	     int show_reloc_info, int keep_relocs)
+{
+	regex_init();
+	read_ehdr(fp);
+	read_shdrs(fp);
+	read_strtabs(fp);
+	read_symtabs(fp);
+	read_relocs(fp);
+	if (show_reloc_info) {
+		print_reloc_info();
+		return;
+	}
+	emit_relocs(as_text, as_bin, fp);
+	if (!keep_relocs)
+		remove_relocs(fp);
+}

arch/mips/boot/tools/relocs.h

+#ifndef RELOCS_H
+#define RELOCS_H
+
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <string.h>
+#include <errno.h>
+#include <unistd.h>
+#include <elf.h>
+#include <byteswap.h>
+#define USE_BSD
+#include <endian.h>
+#include <regex.h>
+
+void die(char *fmt, ...);
+
+/*
+ * Introduced for MIPSr6
+ */
+#ifndef R_MIPS_PC21_S2
+#define R_MIPS_PC21_S2		60
+#endif
+
+#ifndef R_MIPS_PC26_S2
+#define R_MIPS_PC26_S2		61
+#endif
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+enum symtype {
+	S_ABS,
+	S_REL,
+	S_SEG,
+	S_LIN,
+	S_NSYMTYPES
+};
+
+void process_32(FILE *fp, int as_text, int as_bin,
+		int show_reloc_info, int keep_relocs);
+void process_64(FILE *fp, int as_text, int as_bin,
+		int show_reloc_info, int keep_relocs);
+#endif /* RELOCS_H */

arch/mips/boot/tools/relocs_32.c

+#include "relocs.h"
+
+#define ELF_BITS 32
+
+#define ELF_MACHINE		EM_MIPS
+#define ELF_MACHINE_NAME	"MIPS"
+#define SHT_REL_TYPE		SHT_REL
+#define Elf_Rel			ElfW(Rel)
+
+#define ELF_CLASS		ELFCLASS32
+#define ELF_R_SYM(val)		ELF32_R_SYM(val)
+#define ELF_R_TYPE(val)		ELF32_R_TYPE(val)
+#define ELF_ST_TYPE(o)		ELF32_ST_TYPE(o)
+#define ELF_ST_BIND(o)		ELF32_ST_BIND(o)
+#define ELF_ST_VISIBILITY(o)	ELF32_ST_VISIBILITY(o)
+
+#include "relocs.c"

arch/mips/boot/tools/relocs_64.c

+#include "relocs.h"
+
+#define ELF_BITS 64
+
+#define ELF_MACHINE             EM_MIPS
+#define ELF_MACHINE_NAME        "MIPS64"
+#define SHT_REL_TYPE            SHT_RELA
+#define Elf_Rel                 Elf64_Rela
+
+typedef uint8_t Elf64_Byte;
+
+typedef struct {
+	Elf64_Word r_sym;	/* Symbol index.  */
+	Elf64_Byte r_ssym;	/* Special symbol.  */
+	Elf64_Byte r_type3;	/* Third relocation.  */
+	Elf64_Byte r_type2;	/* Second relocation.  */
+	Elf64_Byte r_type;	/* First relocation.  */
+} Elf64_Mips_Rela;
+
+#define ELF_CLASS               ELFCLASS64
+#define ELF_R_SYM(val)          (((Elf64_Mips_Rela *)(&val))->r_sym)
+#define ELF_R_TYPE(val)         (((Elf64_Mips_Rela *)(&val))->r_type)
+#define ELF_ST_TYPE(o)          ELF64_ST_TYPE(o)
+#define ELF_ST_BIND(o)          ELF64_ST_BIND(o)
+#define ELF_ST_VISIBILITY(o)    ELF64_ST_VISIBILITY(o)
+
+#include "relocs.c"

arch/mips/boot/tools/relocs_main.c

+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+#include <endian.h>
+#include <elf.h>
+
+#include "relocs.h"
+
+void die(char *fmt, ...)
+{
+	va_list ap;
+
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	exit(1);
+}
+
+static void usage(void)
+{
+	die("relocs [--reloc-info|--text|--bin|--keep] vmlinux\n");
+}
+
+int main(int argc, char **argv)
+{
+	int show_reloc_info, as_text, as_bin, keep_relocs;
+	const char *fname;
+	FILE *fp;
+	int i;
+	unsigned char e_ident[EI_NIDENT];
+
+	show_reloc_info = 0;
+	as_text = 0;
+	as_bin = 0;
+	keep_relocs = 0;
+	fname = NULL;
+	for (i = 1; i < argc; i++) {
+		char *arg = argv[i];
+
+		if (*arg == '-') {
+			if (strcmp(arg, "--reloc-info") == 0) {
+				show_reloc_info = 1;
+				continue;
+			}
+			if (strcmp(arg, "--text") == 0) {
+				as_text = 1;
+				continue;
+			}
+			if (strcmp(arg, "--bin") == 0) {
+				as_bin = 1;
+				continue;
+			}
+			if (strcmp(arg, "--keep") == 0) {
+				keep_relocs = 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));
+
+	if (fread(&e_ident, 1, EI_NIDENT, fp) != EI_NIDENT)
+		die("Cannot read %s: %s", fname, strerror(errno));
+
+	rewind(fp);
+	if (e_ident[EI_CLASS] == ELFCLASS64)
+		process_64(fp, as_text,  as_bin, show_reloc_info, keep_relocs);
+	else
+		process_32(fp, as_text, as_bin, show_reloc_info, keep_relocs);
+	fclose(fp);
+	return 0;
+}