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relocs.c

#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <elf.h>
#include <byteswap.h>
#define USE_BSD
#include <endian.h>

#define MAX_SHDRS 100
#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
static Elf32_Ehdr ehdr;
static Elf32_Shdr shdr[MAX_SHDRS];
static Elf32_Sym  *symtab[MAX_SHDRS];
static Elf32_Rel  *reltab[MAX_SHDRS];
static char *strtab[MAX_SHDRS];
static unsigned long reloc_count, reloc_idx;
static unsigned long *relocs;

/*
 * Following symbols have been audited. There values are constant and do
 * not change if bzImage is loaded at a different physical address than
 * the address for which it has been compiled. Don't warn user about
 * absolute relocations present w.r.t these symbols.
 */
static const char* safe_abs_relocs[] = {
            "__kernel_vsyscall",
            "__kernel_rt_sigreturn",
            "__kernel_sigreturn",
            "SYSENTER_RETURN",
            "VDSO_NOTE_MASK",
            "xen_irq_disable_direct_reloc",
            "xen_save_fl_direct_reloc",
};

static int is_safe_abs_reloc(const char* sym_name)
{
      int i;

      for(i = 0; i < ARRAY_SIZE(safe_abs_relocs); i++) {
            if (!strcmp(sym_name, safe_abs_relocs[i]))
                  /* Match found */
                  return 1;
      }
      if (strncmp(sym_name, "__crc_", 6) == 0)
            return 1;
      return 0;
}

static void die(char *fmt, ...)
{
      va_list ap;
      va_start(ap, fmt);
      vfprintf(stderr, fmt, ap);
      va_end(ap);
      exit(1);
}

static const char *sym_type(unsigned type)
{
      static const char *type_name[] = {
#define SYM_TYPE(X) [X] = #X
            SYM_TYPE(STT_NOTYPE),
            SYM_TYPE(STT_OBJECT),
            SYM_TYPE(STT_FUNC),
            SYM_TYPE(STT_SECTION),
            SYM_TYPE(STT_FILE),
            SYM_TYPE(STT_COMMON),
            SYM_TYPE(STT_TLS),
#undef SYM_TYPE
      };
      const char *name = "unknown sym type name";
      if (type < ARRAY_SIZE(type_name)) {
            name = type_name[type];
      }
      return name;
}

static const char *sym_bind(unsigned bind)
{
      static const char *bind_name[] = {
#define SYM_BIND(X) [X] = #X
            SYM_BIND(STB_LOCAL),
            SYM_BIND(STB_GLOBAL),
            SYM_BIND(STB_WEAK),
#undef SYM_BIND
      };
      const char *name = "unknown sym bind name";
      if (bind < ARRAY_SIZE(bind_name)) {
            name = bind_name[bind];
      }
      return name;
}

static const char *sym_visibility(unsigned visibility)
{
      static const char *visibility_name[] = {
#define SYM_VISIBILITY(X) [X] = #X
            SYM_VISIBILITY(STV_DEFAULT),
            SYM_VISIBILITY(STV_INTERNAL),
            SYM_VISIBILITY(STV_HIDDEN),
            SYM_VISIBILITY(STV_PROTECTED),
#undef SYM_VISIBILITY
      };
      const char *name = "unknown sym visibility name";
      if (visibility < ARRAY_SIZE(visibility_name)) {
            name = visibility_name[visibility];
      }
      return name;
}

static const char *rel_type(unsigned type)
{
      static const char *type_name[] = {
#define REL_TYPE(X) [X] = #X
            REL_TYPE(R_386_NONE),
            REL_TYPE(R_386_32),
            REL_TYPE(R_386_PC32),
            REL_TYPE(R_386_GOT32),
            REL_TYPE(R_386_PLT32),
            REL_TYPE(R_386_COPY),
            REL_TYPE(R_386_GLOB_DAT),
            REL_TYPE(R_386_JMP_SLOT),
            REL_TYPE(R_386_RELATIVE),
            REL_TYPE(R_386_GOTOFF),
            REL_TYPE(R_386_GOTPC),
#undef REL_TYPE
      };
      const char *name = "unknown type rel type name";
      if (type < ARRAY_SIZE(type_name)) {
            name = type_name[type];
      }
      return name;
}

static const char *sec_name(unsigned shndx)
{
      const char *sec_strtab;
      const char *name;
      sec_strtab = strtab[ehdr.e_shstrndx];
      name = "<noname>";
      if (shndx < ehdr.e_shnum) {
            name = sec_strtab + shdr[shndx].sh_name;
      }
      else if (shndx == SHN_ABS) {
            name = "ABSOLUTE";
      }
      else if (shndx == SHN_COMMON) {
            name = "COMMON";
      }
      return name;
}

static const char *sym_name(const char *sym_strtab, Elf32_Sym *sym)
{
      const char *name;
      name = "<noname>";
      if (sym->st_name) {
            name = sym_strtab + sym->st_name;
      }
      else {
            name = sec_name(shdr[sym->st_shndx].sh_name);
      }
      return name;
}



#if BYTE_ORDER == LITTLE_ENDIAN
#define le16_to_cpu(val) (val)
#define le32_to_cpu(val) (val)
#endif
#if BYTE_ORDER == BIG_ENDIAN
#define le16_to_cpu(val) bswap_16(val)
#define le32_to_cpu(val) bswap_32(val)
#endif

static uint16_t elf16_to_cpu(uint16_t val)
{
      return le16_to_cpu(val);
}

static uint32_t elf32_to_cpu(uint32_t val)
{
      return le32_to_cpu(val);
}

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, 4) != 0) {
            die("No ELF magic\n");
      }
      if (ehdr.e_ident[EI_CLASS] != ELFCLASS32) {
            die("Not a 32 bit executable\n");
      }
      if (ehdr.e_ident[EI_DATA] != ELFDATA2LSB) {
            die("Not a LSB ELF executable\n");
      }
      if (ehdr.e_ident[EI_VERSION] != EV_CURRENT) {
            die("Unknown ELF version\n");
      }
      /* Convert the fields to native endian */
      ehdr.e_type      = elf16_to_cpu(ehdr.e_type);
      ehdr.e_machine   = elf16_to_cpu(ehdr.e_machine);
      ehdr.e_version   = elf32_to_cpu(ehdr.e_version);
      ehdr.e_entry     = elf32_to_cpu(ehdr.e_entry);
      ehdr.e_phoff     = elf32_to_cpu(ehdr.e_phoff);
      ehdr.e_shoff     = elf32_to_cpu(ehdr.e_shoff);
      ehdr.e_flags     = elf32_to_cpu(ehdr.e_flags);
      ehdr.e_ehsize    = elf16_to_cpu(ehdr.e_ehsize);
      ehdr.e_phentsize = elf16_to_cpu(ehdr.e_phentsize);
      ehdr.e_phnum     = elf16_to_cpu(ehdr.e_phnum);
      ehdr.e_shentsize = elf16_to_cpu(ehdr.e_shentsize);
      ehdr.e_shnum     = elf16_to_cpu(ehdr.e_shnum);
      ehdr.e_shstrndx  = elf16_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 != EM_386) {
            die("Not for x86\n");
      }
      if (ehdr.e_version != EV_CURRENT) {
            die("Unknown ELF version\n");
      }
      if (ehdr.e_ehsize != sizeof(Elf32_Ehdr)) {
            die("Bad Elf header size\n");
      }
      if (ehdr.e_phentsize != sizeof(Elf32_Phdr)) {
            die("Bad program header entry\n");
      }
      if (ehdr.e_shentsize != sizeof(Elf32_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;
      if (ehdr.e_shnum > MAX_SHDRS) {
            die("%d section headers supported: %d\n",
                  ehdr.e_shnum, MAX_SHDRS);
      }
      if (fseek(fp, ehdr.e_shoff, SEEK_SET) < 0) {
            die("Seek to %d failed: %s\n",
                  ehdr.e_shoff, strerror(errno));
      }
      if (fread(&shdr, sizeof(shdr[0]), ehdr.e_shnum, fp) != ehdr.e_shnum) {
            die("Cannot read ELF section headers: %s\n",
                  strerror(errno));
      }
      for(i = 0; i < ehdr.e_shnum; i++) {
            shdr[i].sh_name      = elf32_to_cpu(shdr[i].sh_name);
            shdr[i].sh_type      = elf32_to_cpu(shdr[i].sh_type);
            shdr[i].sh_flags     = elf32_to_cpu(shdr[i].sh_flags);
            shdr[i].sh_addr      = elf32_to_cpu(shdr[i].sh_addr);
            shdr[i].sh_offset    = elf32_to_cpu(shdr[i].sh_offset);
            shdr[i].sh_size      = elf32_to_cpu(shdr[i].sh_size);
            shdr[i].sh_link      = elf32_to_cpu(shdr[i].sh_link);
            shdr[i].sh_info      = elf32_to_cpu(shdr[i].sh_info);
            shdr[i].sh_addralign = elf32_to_cpu(shdr[i].sh_addralign);
            shdr[i].sh_entsize   = elf32_to_cpu(shdr[i].sh_entsize);
      }

}

static void read_strtabs(FILE *fp)
{
      int i;
      for(i = 0; i < ehdr.e_shnum; i++) {
            if (shdr[i].sh_type != SHT_STRTAB) {
                  continue;
            }
            strtab[i] = malloc(shdr[i].sh_size);
            if (!strtab[i]) {
                  die("malloc of %d bytes for strtab 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(strtab[i], 1, shdr[i].sh_size, fp) != shdr[i].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++) {
            if (shdr[i].sh_type != SHT_SYMTAB) {
                  continue;
            }
            symtab[i] = malloc(shdr[i].sh_size);
            if (!symtab[i]) {
                  die("malloc of %d bytes for symtab 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(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;
}

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