get_unmapped_area handles MAP_FIXED on i386

[pv_ops_mirror.git] / scripts / mod / modpost.c

/* Postprocess module symbol versions
 *
 * Copyright 2003       Kai Germaschewski
 * Copyright 2002-2004  Rusty Russell, IBM Corporation
 * Copyright 2006       Sam Ravnborg
 * Based in part on module-init-tools/depmod.c,file2alias
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 *
 * Usage: modpost vmlinux module1.o module2.o ...
 */

#include <ctype.h>
#include "modpost.h"
#include "../../include/linux/license.h"

/* Are we using CONFIG_MODVERSIONS? */
int modversions = 0;
/* Warn about undefined symbols? (do so if we have vmlinux) */
int have_vmlinux = 0;
/* Is CONFIG_MODULE_SRCVERSION_ALL set? */
static int all_versions = 0;
/* If we are modposting external module set to 1 */
static int external_module = 0;
/* Only warn about unresolved symbols */
static int warn_unresolved = 0;
/* How a symbol is exported */
enum export {
        export_plain,      export_unused,     export_gpl,
        export_unused_gpl, export_gpl_future, export_unknown
};

void fatal(const char *fmt, ...)
{
        va_list arglist;

        fprintf(stderr, "FATAL: ");

        va_start(arglist, fmt);
        vfprintf(stderr, fmt, arglist);
        va_end(arglist);

        exit(1);
}

void warn(const char *fmt, ...)
{
        va_list arglist;

        fprintf(stderr, "WARNING: ");

        va_start(arglist, fmt);
        vfprintf(stderr, fmt, arglist);
        va_end(arglist);
}

void merror(const char *fmt, ...)
{
        va_list arglist;

        fprintf(stderr, "ERROR: ");

        va_start(arglist, fmt);
        vfprintf(stderr, fmt, arglist);
        va_end(arglist);
}

static int is_vmlinux(const char *modname)
{
        const char *myname;

        if ((myname = strrchr(modname, '/')))
                myname++;
        else
                myname = modname;

        return strcmp(myname, "vmlinux") == 0;
}

void *do_nofail(void *ptr, const char *expr)
{
        if (!ptr) {
                fatal("modpost: Memory allocation failure: %s.\n", expr);
        }
        return ptr;
}

/* A list of all modules we processed */

static struct module *modules;

static struct module *find_module(char *modname)
{
        struct module *mod;

        for (mod = modules; mod; mod = mod->next)
                if (strcmp(mod->name, modname) == 0)
                        break;
        return mod;
}

static struct module *new_module(char *modname)
{
        struct module *mod;
        char *p, *s;

        mod = NOFAIL(malloc(sizeof(*mod)));
        memset(mod, 0, sizeof(*mod));
        p = NOFAIL(strdup(modname));

        /* strip trailing .o */
        if ((s = strrchr(p, '.')) != NULL)
                if (strcmp(s, ".o") == 0)
                        *s = '\0';

        /* add to list */
        mod->name = p;
        mod->gpl_compatible = -1;
        mod->next = modules;
        modules = mod;

        return mod;
}

/* A hash of all exported symbols,
 * struct symbol is also used for lists of unresolved symbols */

#define SYMBOL_HASH_SIZE 1024

struct symbol {
        struct symbol *next;
        struct module *module;
        unsigned int crc;
        int crc_valid;
        unsigned int weak:1;
        unsigned int vmlinux:1;    /* 1 if symbol is defined in vmlinux */
        unsigned int kernel:1;     /* 1 if symbol is from kernel
                                    *  (only for external modules) **/
        unsigned int preloaded:1;  /* 1 if symbol from Module.symvers */
        enum export  export;       /* Type of export */
        char name[0];
};

static struct symbol *symbolhash[SYMBOL_HASH_SIZE];

/* This is based on the hash agorithm from gdbm, via tdb */
static inline unsigned int tdb_hash(const char *name)
{
        unsigned value; /* Used to compute the hash value.  */
        unsigned   i;   /* Used to cycle through random values. */

        /* Set the initial value from the key size. */
        for (value = 0x238F13AF * strlen(name), i=0; name[i]; i++)
                value = (value + (((unsigned char *)name)[i] << (i*5 % 24)));

        return (1103515243 * value + 12345);
}

/**
 * Allocate a new symbols for use in the hash of exported symbols or
 * the list of unresolved symbols per module
 **/
static struct symbol *alloc_symbol(const char *name, unsigned int weak,
                                   struct symbol *next)
{
        struct symbol *s = NOFAIL(malloc(sizeof(*s) + strlen(name) + 1));

        memset(s, 0, sizeof(*s));
        strcpy(s->name, name);
        s->weak = weak;
        s->next = next;
        return s;
}

/* For the hash of exported symbols */
static struct symbol *new_symbol(const char *name, struct module *module,
                                 enum export export)
{
        unsigned int hash;
        struct symbol *new;

        hash = tdb_hash(name) % SYMBOL_HASH_SIZE;
        new = symbolhash[hash] = alloc_symbol(name, 0, symbolhash[hash]);
        new->module = module;
        new->export = export;
        return new;
}

static struct symbol *find_symbol(const char *name)
{
        struct symbol *s;

        /* For our purposes, .foo matches foo.  PPC64 needs this. */
        if (name[0] == '.')
                name++;

        for (s = symbolhash[tdb_hash(name) % SYMBOL_HASH_SIZE]; s; s=s->next) {
                if (strcmp(s->name, name) == 0)
                        return s;
        }
        return NULL;
}

static struct {
        const char *str;
        enum export export;
} export_list[] = {
        { .str = "EXPORT_SYMBOL",            .export = export_plain },
        { .str = "EXPORT_UNUSED_SYMBOL",     .export = export_unused },
        { .str = "EXPORT_SYMBOL_GPL",        .export = export_gpl },
        { .str = "EXPORT_UNUSED_SYMBOL_GPL", .export = export_unused_gpl },
        { .str = "EXPORT_SYMBOL_GPL_FUTURE", .export = export_gpl_future },
        { .str = "(unknown)",                .export = export_unknown },
};


static const char *export_str(enum export ex)
{
        return export_list[ex].str;
}

static enum export export_no(const char * s)
{
        int i;
        if (!s)
                return export_unknown;
        for (i = 0; export_list[i].export != export_unknown; i++) {
                if (strcmp(export_list[i].str, s) == 0)
                        return export_list[i].export;
        }
        return export_unknown;
}

static enum export export_from_sec(struct elf_info *elf, Elf_Section sec)
{
        if (sec == elf->export_sec)
                return export_plain;
        else if (sec == elf->export_unused_sec)
                return export_unused;
        else if (sec == elf->export_gpl_sec)
                return export_gpl;
        else if (sec == elf->export_unused_gpl_sec)
                return export_unused_gpl;
        else if (sec == elf->export_gpl_future_sec)
                return export_gpl_future;
        else
                return export_unknown;
}

/**
 * Add an exported symbol - it may have already been added without a
 * CRC, in this case just update the CRC
 **/
static struct symbol *sym_add_exported(const char *name, struct module *mod,
                                       enum export export)
{
        struct symbol *s = find_symbol(name);

        if (!s) {
                s = new_symbol(name, mod, export);
        } else {
                if (!s->preloaded) {
                        warn("%s: '%s' exported twice. Previous export "
                             "was in %s%s\n", mod->name, name,
                             s->module->name,
                             is_vmlinux(s->module->name) ?"":".ko");
                }
        }
        s->preloaded = 0;
        s->vmlinux   = is_vmlinux(mod->name);
        s->kernel    = 0;
        s->export    = export;
        return s;
}

static void sym_update_crc(const char *name, struct module *mod,
                           unsigned int crc, enum export export)
{
        struct symbol *s = find_symbol(name);

        if (!s)
                s = new_symbol(name, mod, export);
        s->crc = crc;
        s->crc_valid = 1;
}

void *grab_file(const char *filename, unsigned long *size)
{
        struct stat st;
        void *map;
        int fd;

        fd = open(filename, O_RDONLY);
        if (fd < 0 || fstat(fd, &st) != 0)
                return NULL;

        *size = st.st_size;
        map = mmap(NULL, *size, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
        close(fd);

        if (map == MAP_FAILED)
                return NULL;
        return map;
}

/**
  * Return a copy of the next line in a mmap'ed file.
  * spaces in the beginning of the line is trimmed away.
  * Return a pointer to a static buffer.
  **/
char* get_next_line(unsigned long *pos, void *file, unsigned long size)
{
        static char line[4096];
        int skip = 1;
        size_t len = 0;
        signed char *p = (signed char *)file + *pos;
        char *s = line;

        for (; *pos < size ; (*pos)++)
        {
                if (skip && isspace(*p)) {
                        p++;
                        continue;
                }
                skip = 0;
                if (*p != '\n' && (*pos < size)) {
                        len++;
                        *s++ = *p++;
                        if (len > 4095)
                                break; /* Too long, stop */
                } else {
                        /* End of string */
                        *s = '\0';
                        return line;
                }
        }
        /* End of buffer */
        return NULL;
}

void release_file(void *file, unsigned long size)
{
        munmap(file, size);
}

static int parse_elf(struct elf_info *info, const char *filename)
{
        unsigned int i;
        Elf_Ehdr *hdr;
        Elf_Shdr *sechdrs;
        Elf_Sym  *sym;

        hdr = grab_file(filename, &info->size);
        if (!hdr) {
                perror(filename);
                exit(1);
        }
        info->hdr = hdr;
        if (info->size < sizeof(*hdr)) {
                /* file too small, assume this is an empty .o file */
                return 0;
        }
        /* Is this a valid ELF file? */
        if ((hdr->e_ident[EI_MAG0] != ELFMAG0) ||
            (hdr->e_ident[EI_MAG1] != ELFMAG1) ||
            (hdr->e_ident[EI_MAG2] != ELFMAG2) ||
            (hdr->e_ident[EI_MAG3] != ELFMAG3)) {
                /* Not an ELF file - silently ignore it */
                return 0;
        }
        /* Fix endianness in ELF header */
        hdr->e_shoff    = TO_NATIVE(hdr->e_shoff);
        hdr->e_shstrndx = TO_NATIVE(hdr->e_shstrndx);
        hdr->e_shnum    = TO_NATIVE(hdr->e_shnum);
        hdr->e_machine  = TO_NATIVE(hdr->e_machine);
        sechdrs = (void *)hdr + hdr->e_shoff;
        info->sechdrs = sechdrs;

        /* Fix endianness in section headers */
        for (i = 0; i < hdr->e_shnum; i++) {
                sechdrs[i].sh_type   = TO_NATIVE(sechdrs[i].sh_type);
                sechdrs[i].sh_offset = TO_NATIVE(sechdrs[i].sh_offset);
                sechdrs[i].sh_size   = TO_NATIVE(sechdrs[i].sh_size);
                sechdrs[i].sh_link   = TO_NATIVE(sechdrs[i].sh_link);
                sechdrs[i].sh_name   = TO_NATIVE(sechdrs[i].sh_name);
        }
        /* Find symbol table. */
        for (i = 1; i < hdr->e_shnum; i++) {
                const char *secstrings
                        = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
                const char *secname;

                if (sechdrs[i].sh_offset > info->size) {
                        fatal("%s is truncated. sechdrs[i].sh_offset=%u > sizeof(*hrd)=%ul\n", filename, (unsigned int)sechdrs[i].sh_offset, sizeof(*hdr));
                        return 0;
                }
                secname = secstrings + sechdrs[i].sh_name;
                if (strcmp(secname, ".modinfo") == 0) {
                        info->modinfo = (void *)hdr + sechdrs[i].sh_offset;
                        info->modinfo_len = sechdrs[i].sh_size;
                } else if (strcmp(secname, "__ksymtab") == 0)
                        info->export_sec = i;
                else if (strcmp(secname, "__ksymtab_unused") == 0)
                        info->export_unused_sec = i;
                else if (strcmp(secname, "__ksymtab_gpl") == 0)
                        info->export_gpl_sec = i;
                else if (strcmp(secname, "__ksymtab_unused_gpl") == 0)
                        info->export_unused_gpl_sec = i;
                else if (strcmp(secname, "__ksymtab_gpl_future") == 0)
                        info->export_gpl_future_sec = i;

                if (sechdrs[i].sh_type != SHT_SYMTAB)
                        continue;

                info->symtab_start = (void *)hdr + sechdrs[i].sh_offset;
                info->symtab_stop  = (void *)hdr + sechdrs[i].sh_offset
                                                 + sechdrs[i].sh_size;
                info->strtab       = (void *)hdr +
                                     sechdrs[sechdrs[i].sh_link].sh_offset;
        }
        if (!info->symtab_start) {
                fatal("%s has no symtab?\n", filename);
        }
        /* Fix endianness in symbols */
        for (sym = info->symtab_start; sym < info->symtab_stop; sym++) {
                sym->st_shndx = TO_NATIVE(sym->st_shndx);
                sym->st_name  = TO_NATIVE(sym->st_name);
                sym->st_value = TO_NATIVE(sym->st_value);
                sym->st_size  = TO_NATIVE(sym->st_size);
        }
        return 1;
}

static void parse_elf_finish(struct elf_info *info)
{
        release_file(info->hdr, info->size);
}

#define CRC_PFX     MODULE_SYMBOL_PREFIX "__crc_"
#define KSYMTAB_PFX MODULE_SYMBOL_PREFIX "__ksymtab_"

static void handle_modversions(struct module *mod, struct elf_info *info,
                               Elf_Sym *sym, const char *symname)
{
        unsigned int crc;
        enum export export = export_from_sec(info, sym->st_shndx);

        switch (sym->st_shndx) {
        case SHN_COMMON:
                warn("\"%s\" [%s] is COMMON symbol\n", symname, mod->name);
                break;
        case SHN_ABS:
                /* CRC'd symbol */
                if (memcmp(symname, CRC_PFX, strlen(CRC_PFX)) == 0) {
                        crc = (unsigned int) sym->st_value;
                        sym_update_crc(symname + strlen(CRC_PFX), mod, crc,
                                        export);
                }
                break;
        case SHN_UNDEF:
                /* undefined symbol */
                if (ELF_ST_BIND(sym->st_info) != STB_GLOBAL &&
                    ELF_ST_BIND(sym->st_info) != STB_WEAK)
                        break;
                /* ignore global offset table */
                if (strcmp(symname, "_GLOBAL_OFFSET_TABLE_") == 0)
                        break;
                /* ignore __this_module, it will be resolved shortly */
                if (strcmp(symname, MODULE_SYMBOL_PREFIX "__this_module") == 0)
                        break;
/* cope with newer glibc (2.3.4 or higher) STT_ definition in elf.h */
#if defined(STT_REGISTER) || defined(STT_SPARC_REGISTER)
/* add compatibility with older glibc */
#ifndef STT_SPARC_REGISTER
#define STT_SPARC_REGISTER STT_REGISTER
#endif
                if (info->hdr->e_machine == EM_SPARC ||
                    info->hdr->e_machine == EM_SPARCV9) {
                        /* Ignore register directives. */
                        if (ELF_ST_TYPE(sym->st_info) == STT_SPARC_REGISTER)
                                break;
                        if (symname[0] == '.') {
                                char *munged = strdup(symname);
                                munged[0] = '_';
                                munged[1] = toupper(munged[1]);
                                symname = munged;
                        }
                }
#endif

                if (memcmp(symname, MODULE_SYMBOL_PREFIX,
                           strlen(MODULE_SYMBOL_PREFIX)) == 0)
                        mod->unres = alloc_symbol(symname +
                                                  strlen(MODULE_SYMBOL_PREFIX),
                                                  ELF_ST_BIND(sym->st_info) == STB_WEAK,
                                                  mod->unres);
                break;
        default:
                /* All exported symbols */
                if (memcmp(symname, KSYMTAB_PFX, strlen(KSYMTAB_PFX)) == 0) {
                        sym_add_exported(symname + strlen(KSYMTAB_PFX), mod,
                                        export);
                }
                if (strcmp(symname, MODULE_SYMBOL_PREFIX "init_module") == 0)
                        mod->has_init = 1;
                if (strcmp(symname, MODULE_SYMBOL_PREFIX "cleanup_module") == 0)
                        mod->has_cleanup = 1;
                break;
        }
}

/**
 * Parse tag=value strings from .modinfo section
 **/
static char *next_string(char *string, unsigned long *secsize)
{
        /* Skip non-zero chars */
        while (string[0]) {
                string++;
                if ((*secsize)-- <= 1)
                        return NULL;
        }

        /* Skip any zero padding. */
        while (!string[0]) {
                string++;
                if ((*secsize)-- <= 1)
                        return NULL;
        }
        return string;
}

static char *get_next_modinfo(void *modinfo, unsigned long modinfo_len,
                              const char *tag, char *info)
{
        char *p;
        unsigned int taglen = strlen(tag);
        unsigned long size = modinfo_len;

        if (info) {
                size -= info - (char *)modinfo;
                modinfo = next_string(info, &size);
        }

        for (p = modinfo; p; p = next_string(p, &size)) {
                if (strncmp(p, tag, taglen) == 0 && p[taglen] == '=')
                        return p + taglen + 1;
        }
        return NULL;
}

static char *get_modinfo(void *modinfo, unsigned long modinfo_len,
                         const char *tag)

{
        return get_next_modinfo(modinfo, modinfo_len, tag, NULL);
}

/**
 * Test if string s ends in string sub
 * return 0 if match
 **/
static int strrcmp(const char *s, const char *sub)
{
        int slen, sublen;

        if (!s || !sub)
                return 1;

        slen = strlen(s);
        sublen = strlen(sub);

        if ((slen == 0) || (sublen == 0))
                return 1;

        if (sublen > slen)
                return 1;

        return memcmp(s + slen - sublen, sub, sublen);
}

/**
 * Whitelist to allow certain references to pass with no warning.
 * Pattern 1:
 *   If a module parameter is declared __initdata and permissions=0
 *   then this is legal despite the warning generated.
 *   We cannot see value of permissions here, so just ignore
 *   this pattern.
 *   The pattern is identified by:
 *   tosec   = .init.data
 *   fromsec = .data*
 *   atsym   =__param*
 *
 * Pattern 2:
 *   Many drivers utilise a *driver container with references to
 *   add, remove, probe functions etc.
 *   These functions may often be marked __init and we do not want to
 *   warn here.
 *   the pattern is identified by:
 *   tosec   = .init.text | .exit.text | .init.data
 *   fromsec = .data
 *   atsym = *driver, *_template, *_sht, *_ops, *_probe, *probe_one, *_console
 *
 * Pattern 3:
 *   Whitelist all references from .pci_fixup* section to .init.text
 *   This is part of the PCI init when built-in
 *
 * Pattern 4:
 *   Whitelist all refereces from .text.head to .init.data
 *   Whitelist all refereces from .text.head to .init.text
 *
 * Pattern 5:
 *   Some symbols belong to init section but still it is ok to reference
 *   these from non-init sections as these symbols don't have any memory
 *   allocated for them and symbol address and value are same. So even
 *   if init section is freed, its ok to reference those symbols.
 *   For ex. symbols marking the init section boundaries.
 *   This pattern is identified by
 *   refsymname = __init_begin, _sinittext, _einittext
 *
 * Pattern 6:
 *   During the early init phase we have references from .init.text to
 *   .text we have an intended section mismatch - do not warn about it.
 *   See kernel_init() in init/main.c
 *   tosec   = .init.text
 *   fromsec = .text
 *   atsym = kernel_init
 *
 * Pattern 7:
 *  Logos used in drivers/video/logo reside in __initdata but the
 *  funtion that references them are EXPORT_SYMBOL() so cannot be
 *  marker __init. So we whitelist them here.
 *  The pattern is:
 *  tosec      = .init.data
 *  fromsec    = .text*
 *  refsymname = logo_
 *
 * Pattern 8:
 *  Symbols contained in .paravirtprobe may safely reference .init.text.
 *  The pattern is:
 *  tosec   = .init.text
 *  fromsec  = .paravirtprobe
 *
 **/
static int secref_whitelist(const char *modname, const char *tosec,
                            const char *fromsec, const char *atsym,
                            const char *refsymname)
{
        int f1 = 1, f2 = 1;
        const char **s;
        const char *pat2sym[] = {
                "driver",
                "_template", /* scsi uses *_template a lot */
                "_sht",      /* scsi also used *_sht to some extent */
                "_ops",
                "_probe",
                "_probe_one",
                "_console",
                "apic_es7000",
                NULL
        };

        const char *pat3refsym[] = {
                "__init_begin",
                "_sinittext",
                "_einittext",
                NULL
        };

        /* Check for pattern 1 */
        if (strcmp(tosec, ".init.data") != 0)
                f1 = 0;
        if (strncmp(fromsec, ".data", strlen(".data")) != 0)
                f1 = 0;
        if (strncmp(atsym, "__param", strlen("__param")) != 0)
                f1 = 0;

        if (f1)
                return f1;

        /* Check for pattern 2 */
        if ((strcmp(tosec, ".init.text") != 0) &&
            (strcmp(tosec, ".exit.text") != 0) &&
            (strcmp(tosec, ".init.data") != 0))
                f2 = 0;
        if (strcmp(fromsec, ".data") != 0)
                f2 = 0;

        for (s = pat2sym; *s; s++)
                if (strrcmp(atsym, *s) == 0)
                        f1 = 1;
        if (f1 && f2)
                return 1;

        /* Check for pattern 3 */
        if ((strncmp(fromsec, ".pci_fixup", strlen(".pci_fixup")) == 0) &&
            (strcmp(tosec, ".init.text") == 0))
        return 1;

        /* Check for pattern 4 */
        if ((strcmp(fromsec, ".text.head") == 0) &&
                ((strcmp(tosec, ".init.data") == 0) ||
                (strcmp(tosec, ".init.text") == 0)))
        return 1;

        /* Check for pattern 5 */
        for (s = pat3refsym; *s; s++)
                if (strcmp(refsymname, *s) == 0)
                        return 1;

        /* Check for pattern 6 */
        if ((strcmp(tosec, ".init.text") == 0) &&
            (strcmp(fromsec, ".text") == 0) &&
            (strcmp(refsymname, "kernel_init") == 0))
                return 1;

        /* Check for pattern 7 */
        if ((strcmp(tosec, ".init.data") == 0) &&
            (strncmp(fromsec, ".text", strlen(".text")) == 0) &&
            (strncmp(refsymname, "logo_", strlen("logo_")) == 0))
                return 1;

        /* Check for pattern 8 */
        if ((strcmp(tosec, ".init.text") == 0) &&
            (strcmp(fromsec, ".paravirtprobe") == 0))
                return 1;

        return 0;
}

/**
 * Find symbol based on relocation record info.
 * In some cases the symbol supplied is a valid symbol so
 * return refsym. If st_name != 0 we assume this is a valid symbol.
 * In other cases the symbol needs to be looked up in the symbol table
 * based on section and address.
 *  **/
static Elf_Sym *find_elf_symbol(struct elf_info *elf, Elf_Addr addr,
                                Elf_Sym *relsym)
{
        Elf_Sym *sym;

        if (relsym->st_name != 0)
                return relsym;
        for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
                if (sym->st_shndx != relsym->st_shndx)
                        continue;
                if (sym->st_value == addr)
                        return sym;
        }
        return NULL;
}

static inline int is_arm_mapping_symbol(const char *str)
{
        return str[0] == '$' && strchr("atd", str[1])
               && (str[2] == '\0' || str[2] == '.');
}

/*
 * If there's no name there, ignore it; likewise, ignore it if it's
 * one of the magic symbols emitted used by current ARM tools.
 *
 * Otherwise if find_symbols_between() returns those symbols, they'll
 * fail the whitelist tests and cause lots of false alarms ... fixable
 * only by merging __exit and __init sections into __text, bloating
 * the kernel (which is especially evil on embedded platforms).
 */
static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
{
        const char *name = elf->strtab + sym->st_name;

        if (!name || !strlen(name))
                return 0;
        return !is_arm_mapping_symbol(name);
}

/*
 * Find symbols before or equal addr and after addr - in the section sec.
 * If we find two symbols with equal offset prefer one with a valid name.
 * The ELF format may have a better way to detect what type of symbol
 * it is, but this works for now.
 **/
static void find_symbols_between(struct elf_info *elf, Elf_Addr addr,
                                 const char *sec,
                                 Elf_Sym **before, Elf_Sym **after)
{
        Elf_Sym *sym;
        Elf_Ehdr *hdr = elf->hdr;
        Elf_Addr beforediff = ~0;
        Elf_Addr afterdiff = ~0;
        const char *secstrings = (void *)hdr +
                                 elf->sechdrs[hdr->e_shstrndx].sh_offset;

        *before = NULL;
        *after = NULL;

        for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
                const char *symsec;

                if (sym->st_shndx >= SHN_LORESERVE)
                        continue;
                symsec = secstrings + elf->sechdrs[sym->st_shndx].sh_name;
                if (strcmp(symsec, sec) != 0)
                        continue;
                if (!is_valid_name(elf, sym))
                        continue;
                if (sym->st_value <= addr) {
                        if ((addr - sym->st_value) < beforediff) {
                                beforediff = addr - sym->st_value;
                                *before = sym;
                        }
                        else if ((addr - sym->st_value) == beforediff) {
                                *before = sym;
                        }
                }
                else
                {
                        if ((sym->st_value - addr) < afterdiff) {
                                afterdiff = sym->st_value - addr;
                                *after = sym;
                        }
                        else if ((sym->st_value - addr) == afterdiff) {
                                *after = sym;
                        }
                }
        }
}

/**
 * Print a warning about a section mismatch.
 * Try to find symbols near it so user can find it.
 * Check whitelist before warning - it may be a false positive.
 **/
static void warn_sec_mismatch(const char *modname, const char *fromsec,
                              struct elf_info *elf, Elf_Sym *sym, Elf_Rela r)
{
        const char *refsymname = "";
        Elf_Sym *before, *after;
        Elf_Sym *refsym;
        Elf_Ehdr *hdr = elf->hdr;
        Elf_Shdr *sechdrs = elf->sechdrs;
        const char *secstrings = (void *)hdr +
                                 sechdrs[hdr->e_shstrndx].sh_offset;
        const char *secname = secstrings + sechdrs[sym->st_shndx].sh_name;

        find_symbols_between(elf, r.r_offset, fromsec, &before, &after);

        refsym = find_elf_symbol(elf, r.r_addend, sym);
        if (refsym && strlen(elf->strtab + refsym->st_name))
                refsymname = elf->strtab + refsym->st_name;

        /* check whitelist - we may ignore it */
        if (before &&
            secref_whitelist(modname, secname, fromsec,
                             elf->strtab + before->st_name, refsymname))
                return;

        if (before && after) {
                warn("%s - Section mismatch: reference to %s:%s from %s "
                     "between '%s' (at offset 0x%llx) and '%s'\n",
                     modname, secname, refsymname, fromsec,
                     elf->strtab + before->st_name,
                     (long long)r.r_offset,
                     elf->strtab + after->st_name);
        } else if (before) {
                warn("%s - Section mismatch: reference to %s:%s from %s "
                     "after '%s' (at offset 0x%llx)\n",
                     modname, secname, refsymname, fromsec,
                     elf->strtab + before->st_name,
                     (long long)r.r_offset);
        } else if (after) {
                warn("%s - Section mismatch: reference to %s:%s from %s "
                     "before '%s' (at offset -0x%llx)\n",
                     modname, secname, refsymname, fromsec,
                     elf->strtab + after->st_name,
                     (long long)r.r_offset);
        } else {
                warn("%s - Section mismatch: reference to %s:%s from %s "
                     "(offset 0x%llx)\n",
                     modname, secname, fromsec, refsymname,
                     (long long)r.r_offset);
        }
}

/**
 * A module includes a number of sections that are discarded
 * either when loaded or when used as built-in.
 * For loaded modules all functions marked __init and all data
 * marked __initdata will be discarded when the module has been intialized.
 * Likewise for modules used built-in the sections marked __exit
 * are discarded because __exit marked function are supposed to be called
 * only when a moduel is unloaded which never happes for built-in modules.
 * The check_sec_ref() function traverses all relocation records
 * to find all references to a section that reference a section that will
 * be discarded and warns about it.
 **/
static void check_sec_ref(struct module *mod, const char *modname,
                          struct elf_info *elf,
                          int section(const char*),
                          int section_ref_ok(const char *))
{
        int i;
        Elf_Sym  *sym;
        Elf_Ehdr *hdr = elf->hdr;
        Elf_Shdr *sechdrs = elf->sechdrs;
        const char *secstrings = (void *)hdr +
                                 sechdrs[hdr->e_shstrndx].sh_offset;

        /* Walk through all sections */
        for (i = 0; i < hdr->e_shnum; i++) {
                const char *name = secstrings + sechdrs[i].sh_name;
                const char *secname;
                Elf_Rela r;
                unsigned int r_sym;
                /* We want to process only relocation sections and not .init */
                if (sechdrs[i].sh_type == SHT_RELA) {
                        Elf_Rela *rela;
                        Elf_Rela *start = (void *)hdr + sechdrs[i].sh_offset;
                        Elf_Rela *stop  = (void*)start + sechdrs[i].sh_size;
                        name += strlen(".rela");
                        if (section_ref_ok(name))
                                continue;

                        for (rela = start; rela < stop; rela++) {
                                r.r_offset = TO_NATIVE(rela->r_offset);
#if KERNEL_ELFCLASS == ELFCLASS64
                                if (hdr->e_machine == EM_MIPS) {
                                        r_sym = ELF64_MIPS_R_SYM(rela->r_info);
                                        r_sym = TO_NATIVE(r_sym);
                                } else {
                                        r.r_info = TO_NATIVE(rela->r_info);
                                        r_sym = ELF_R_SYM(r.r_info);
                                }
#else
                                r.r_info = TO_NATIVE(rela->r_info);
                                r_sym = ELF_R_SYM(r.r_info);
#endif
                                r.r_addend = TO_NATIVE(rela->r_addend);
                                sym = elf->symtab_start + r_sym;
                                /* Skip special sections */
                                if (sym->st_shndx >= SHN_LORESERVE)
                                        continue;

                                secname = secstrings +
                                        sechdrs[sym->st_shndx].sh_name;
                                if (section(secname))
                                        warn_sec_mismatch(modname, name,
                                                          elf, sym, r);
                        }
                } else if (sechdrs[i].sh_type == SHT_REL) {
                        Elf_Rel *rel;
                        Elf_Rel *start = (void *)hdr + sechdrs[i].sh_offset;
                        Elf_Rel *stop  = (void*)start + sechdrs[i].sh_size;
                        name += strlen(".rel");
                        if (section_ref_ok(name))
                                continue;

                        for (rel = start; rel < stop; rel++) {
                                r.r_offset = TO_NATIVE(rel->r_offset);
#if KERNEL_ELFCLASS == ELFCLASS64
                                if (hdr->e_machine == EM_MIPS) {
                                        r_sym = ELF64_MIPS_R_SYM(rel->r_info);
                                        r_sym = TO_NATIVE(r_sym);
                                } else {
                                        r.r_info = TO_NATIVE(rel->r_info);
                                        r_sym = ELF_R_SYM(r.r_info);
                                }
#else
                                r.r_info = TO_NATIVE(rel->r_info);
                                r_sym = ELF_R_SYM(r.r_info);
#endif
                                r.r_addend = 0;
                                sym = elf->symtab_start + r_sym;
                                /* Skip special sections */
                                if (sym->st_shndx >= SHN_LORESERVE)
                                        continue;

                                secname = secstrings +
                                        sechdrs[sym->st_shndx].sh_name;
                                if (section(secname))
                                        warn_sec_mismatch(modname, name,
                                                          elf, sym, r);
                        }
                }
        }
}

/**
 * Functions used only during module init is marked __init and is stored in
 * a .init.text section. Likewise data is marked __initdata and stored in
 * a .init.data section.
 * If this section is one of these sections return 1
 * See include/linux/init.h for the details
 **/
static int init_section(const char *name)
{
        if (strcmp(name, ".init") == 0)
                return 1;
        if (strncmp(name, ".init.", strlen(".init.")) == 0)
                return 1;
        return 0;
}

/**
 * Identify sections from which references to a .init section is OK.
 *
 * Unfortunately references to read only data that referenced .init
 * sections had to be excluded. Almost all of these are false
 * positives, they are created by gcc. The downside of excluding rodata
 * is that there really are some user references from rodata to
 * init code, e.g. drivers/video/vgacon.c:
 *
 * const struct consw vga_con = {
 *        con_startup:            vgacon_startup,
 *
 * where vgacon_startup is __init.  If you want to wade through the false
 * positives, take out the check for rodata.
 **/
static int init_section_ref_ok(const char *name)
{
        const char **s;
        /* Absolute section names */
        const char *namelist1[] = {
                ".init",
                ".opd",   /* see comment [OPD] at exit_section_ref_ok() */
                ".toc1",  /* used by ppc64 */
                ".stab",
                ".data.rel.ro", /* used by parisc64 */
                ".parainstructions",
                ".text.lock",
                "__bug_table", /* used by powerpc for BUG() */
                ".pci_fixup_header",
                ".pci_fixup_final",
                ".pdr",
                "__param",
                "__ex_table",
                ".fixup",
                ".smp_locks",
                ".plt",  /* seen on ARCH=um build on x86_64. Harmless */
                "__ftr_fixup",          /* powerpc cpu feature fixup */
                "__fw_ftr_fixup",       /* powerpc firmware feature fixup */
                NULL
        };
        /* Start of section names */
        const char *namelist2[] = {
                ".init.",
                ".altinstructions",
                ".eh_frame",
                ".debug",
                ".parainstructions",
                ".rodata",
                NULL
        };
        /* part of section name */
        const char *namelist3 [] = {
                ".unwind",  /* sample: IA_64.unwind.init.text */
                NULL
        };

        for (s = namelist1; *s; s++)
                if (strcmp(*s, name) == 0)
                        return 1;
        for (s = namelist2; *s; s++)
                if (strncmp(*s, name, strlen(*s)) == 0)
                        return 1;
        for (s = namelist3; *s; s++)
                if (strstr(name, *s) != NULL)
                        return 1;
        if (strrcmp(name, ".init") == 0)
                return 1;
        return 0;
}

/*
 * Functions used only during module exit is marked __exit and is stored in
 * a .exit.text section. Likewise data is marked __exitdata and stored in
 * a .exit.data section.
 * If this section is one of these sections return 1
 * See include/linux/init.h for the details
 **/
static int exit_section(const char *name)
{
        if (strcmp(name, ".exit.text") == 0)
                return 1;
        if (strcmp(name, ".exit.data") == 0)
                return 1;
        return 0;

}

/*
 * Identify sections from which references to a .exit section is OK.
 *
 * [OPD] Keith Ownes <kaos@sgi.com> commented:
 * For our future {in}sanity, add a comment that this is the ppc .opd
 * section, not the ia64 .opd section.
 * ia64 .opd should not point to discarded sections.
 * [.rodata] like for .init.text we ignore .rodata references -same reason
 **/
static int exit_section_ref_ok(const char *name)
{
        const char **s;
        /* Absolute section names */
        const char *namelist1[] = {
                ".exit.text",
                ".exit.data",
                ".init.text",
                ".rodata",
                ".opd", /* See comment [OPD] */
                ".toc1",  /* used by ppc64 */
                ".altinstructions",
                ".pdr",
                "__bug_table", /* used by powerpc for BUG() */
                ".exitcall.exit",
                ".eh_frame",
                ".parainstructions",
                ".stab",
                "__ex_table",
                ".fixup",
                ".smp_locks",
                ".plt",  /* seen on ARCH=um build on x86_64. Harmless */
                NULL
        };
        /* Start of section names */
        const char *namelist2[] = {
                ".debug",
                NULL
        };
        /* part of section name */
        const char *namelist3 [] = {
                ".unwind",  /* Sample: IA_64.unwind.exit.text */
                NULL
        };

        for (s = namelist1; *s; s++)
                if (strcmp(*s, name) == 0)
                        return 1;
        for (s = namelist2; *s; s++)
                if (strncmp(*s, name, strlen(*s)) == 0)
                        return 1;
        for (s = namelist3; *s; s++)
                if (strstr(name, *s) != NULL)
                        return 1;
        return 0;
}

static void read_symbols(char *modname)
{
        const char *symname;
        char *version;
        char *license;
        struct module *mod;
        struct elf_info info = { };
        Elf_Sym *sym;

        if (!parse_elf(&info, modname))
                return;

        mod = new_module(modname);

        /* When there's no vmlinux, don't print warnings about
         * unresolved symbols (since there'll be too many ;) */
        if (is_vmlinux(modname)) {
                have_vmlinux = 1;
                mod->skip = 1;
        }

        license = get_modinfo(info.modinfo, info.modinfo_len, "license");
        while (license) {
                if (license_is_gpl_compatible(license))
                        mod->gpl_compatible = 1;
                else {
                        mod->gpl_compatible = 0;
                        break;
                }
                license = get_next_modinfo(info.modinfo, info.modinfo_len,
                                           "license", license);
        }

        for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
                symname = info.strtab + sym->st_name;

                handle_modversions(mod, &info, sym, symname);
                handle_moddevtable(mod, &info, sym, symname);
        }
        check_sec_ref(mod, modname, &info, init_section, init_section_ref_ok);
        check_sec_ref(mod, modname, &info, exit_section, exit_section_ref_ok);

        version = get_modinfo(info.modinfo, info.modinfo_len, "version");
        if (version)
                maybe_frob_rcs_version(modname, version, info.modinfo,
                                       version - (char *)info.hdr);
        if (version || (all_versions && !is_vmlinux(modname)))
                get_src_version(modname, mod->srcversion,
                                sizeof(mod->srcversion)-1);

        parse_elf_finish(&info);

        /* Our trick to get versioning for struct_module - it's
         * never passed as an argument to an exported function, so
         * the automatic versioning doesn't pick it up, but it's really
         * important anyhow */
        if (modversions)
                mod->unres = alloc_symbol("struct_module", 0, mod->unres);
}

#define SZ 500

/* We first write the generated file into memory using the
 * following helper, then compare to the file on disk and
 * only update the later if anything changed */

void __attribute__((format(printf, 2, 3))) buf_printf(struct buffer *buf,
                                                      const char *fmt, ...)
{
        char tmp[SZ];
        int len;
        va_list ap;

        va_start(ap, fmt);
        len = vsnprintf(tmp, SZ, fmt, ap);
        buf_write(buf, tmp, len);
        va_end(ap);
}

void buf_write(struct buffer *buf, const char *s, int len)
{
        if (buf->size - buf->pos < len) {
                buf->size += len + SZ;
                buf->p = realloc(buf->p, buf->size);
        }
        strncpy(buf->p + buf->pos, s, len);
        buf->pos += len;
}

static void check_for_gpl_usage(enum export exp, const char *m, const char *s)
{
        const char *e = is_vmlinux(m) ?"":".ko";

        switch (exp) {
        case export_gpl:
                fatal("modpost: GPL-incompatible module %s%s "
                      "uses GPL-only symbol '%s'\n", m, e, s);
                break;
        case export_unused_gpl:
                fatal("modpost: GPL-incompatible module %s%s "
                      "uses GPL-only symbol marked UNUSED '%s'\n", m, e, s);
                break;
        case export_gpl_future:
                warn("modpost: GPL-incompatible module %s%s "
                      "uses future GPL-only symbol '%s'\n", m, e, s);
                break;
        case export_plain:
        case export_unused:
        case export_unknown:
                /* ignore */
                break;
        }
}

static void check_for_unused(enum export exp, const char* m, const char* s)
{
        const char *e = is_vmlinux(m) ?"":".ko";

        switch (exp) {
        case export_unused:
        case export_unused_gpl:
                warn("modpost: module %s%s "
                      "uses symbol '%s' marked UNUSED\n", m, e, s);
                break;
        default:
                /* ignore */
                break;
        }
}

static void check_exports(struct module *mod)
{
        struct symbol *s, *exp;

        for (s = mod->unres; s; s = s->next) {
                const char *basename;
                exp = find_symbol(s->name);
                if (!exp || exp->module == mod)
                        continue;
                basename = strrchr(mod->name, '/');
                if (basename)
                        basename++;
                else
                        basename = mod->name;
                if (!mod->gpl_compatible)
                        check_for_gpl_usage(exp->export, basename, exp->name);
                check_for_unused(exp->export, basename, exp->name);
        }
}

/**
 * Header for the generated file
 **/
static void add_header(struct buffer *b, struct module *mod)
{
        buf_printf(b, "#include <linux/module.h>\n");
        buf_printf(b, "#include <linux/vermagic.h>\n");
        buf_printf(b, "#include <linux/compiler.h>\n");
        buf_printf(b, "\n");
        buf_printf(b, "MODULE_INFO(vermagic, VERMAGIC_STRING);\n");
        buf_printf(b, "\n");
        buf_printf(b, "struct module __this_module\n");
        buf_printf(b, "__attribute__((section(\".gnu.linkonce.this_module\"))) = {\n");
        buf_printf(b, " .name = KBUILD_MODNAME,\n");
        if (mod->has_init)
                buf_printf(b, " .init = init_module,\n");
        if (mod->has_cleanup)
                buf_printf(b, "#ifdef CONFIG_MODULE_UNLOAD\n"
                              " .exit = cleanup_module,\n"
                              "#endif\n");
        buf_printf(b, "};\n");
}

/**
 * Record CRCs for unresolved symbols
 **/
static int add_versions(struct buffer *b, struct module *mod)
{
        struct symbol *s, *exp;
        int err = 0;

        for (s = mod->unres; s; s = s->next) {
                exp = find_symbol(s->name);
                if (!exp || exp->module == mod) {
                        if (have_vmlinux && !s->weak) {
                                if (warn_unresolved) {
                                        warn("\"%s\" [%s.ko] undefined!\n",
                                             s->name, mod->name);
                                } else {
                                        merror("\"%s\" [%s.ko] undefined!\n",
                                                  s->name, mod->name);
                                        err = 1;
                                }
                        }
                        continue;
                }
                s->module = exp->module;
                s->crc_valid = exp->crc_valid;
                s->crc = exp->crc;
        }

        if (!modversions)
                return err;

        buf_printf(b, "\n");
        buf_printf(b, "static const struct modversion_info ____versions[]\n");
        buf_printf(b, "__attribute_used__\n");
        buf_printf(b, "__attribute__((section(\"__versions\"))) = {\n");

        for (s = mod->unres; s; s = s->next) {
                if (!s->module) {
                        continue;
                }
                if (!s->crc_valid) {
                        warn("\"%s\" [%s.ko] has no CRC!\n",
                                s->name, mod->name);
                        continue;
                }
                buf_printf(b, "\t{ %#8x, \"%s\" },\n", s->crc, s->name);
        }

        buf_printf(b, "};\n");

        return err;
}

static void add_depends(struct buffer *b, struct module *mod,
                        struct module *modules)
{
        struct symbol *s;
        struct module *m;
        int first = 1;

        for (m = modules; m; m = m->next) {
                m->seen = is_vmlinux(m->name);
        }

        buf_printf(b, "\n");
        buf_printf(b, "static const char __module_depends[]\n");
        buf_printf(b, "__attribute_used__\n");
        buf_printf(b, "__attribute__((section(\".modinfo\"))) =\n");
        buf_printf(b, "\"depends=");
        for (s = mod->unres; s; s = s->next) {
                const char *p;
                if (!s->module)
                        continue;

                if (s->module->seen)
                        continue;

                s->module->seen = 1;
                if ((p = strrchr(s->module->name, '/')) != NULL)
                        p++;
                else
                        p = s->module->name;
                buf_printf(b, "%s%s", first ? "" : ",", p);
                first = 0;
        }
        buf_printf(b, "\";\n");
}

static void add_srcversion(struct buffer *b, struct module *mod)
{
        if (mod->srcversion[0]) {
                buf_printf(b, "\n");
                buf_printf(b, "MODULE_INFO(srcversion, \"%s\");\n",
                           mod->srcversion);
        }
}

static void write_if_changed(struct buffer *b, const char *fname)
{
        char *tmp;
        FILE *file;
        struct stat st;

        file = fopen(fname, "r");
        if (!file)
                goto write;

        if (fstat(fileno(file), &st) < 0)
                goto close_write;

        if (st.st_size != b->pos)
                goto close_write;

        tmp = NOFAIL(malloc(b->pos));
        if (fread(tmp, 1, b->pos, file) != b->pos)
                goto free_write;

        if (memcmp(tmp, b->p, b->pos) != 0)
                goto free_write;

        free(tmp);
        fclose(file);
        return;

 free_write:
        free(tmp);
 close_write:
        fclose(file);
 write:
        file = fopen(fname, "w");
        if (!file) {
                perror(fname);
                exit(1);
        }
        if (fwrite(b->p, 1, b->pos, file) != b->pos) {
                perror(fname);
                exit(1);
        }
        fclose(file);
}

/* parse Module.symvers file. line format:
 * 0x12345678<tab>symbol<tab>module[[<tab>export]<tab>something]
 **/
static void read_dump(const char *fname, unsigned int kernel)
{
        unsigned long size, pos = 0;
        void *file = grab_file(fname, &size);
        char *line;

        if (!file)
                /* No symbol versions, silently ignore */
                return;

        while ((line = get_next_line(&pos, file, size))) {
                char *symname, *modname, *d, *export, *end;
                unsigned int crc;
                struct module *mod;
                struct symbol *s;

                if (!(symname = strchr(line, '\t')))
                        goto fail;
                *symname++ = '\0';
                if (!(modname = strchr(symname, '\t')))
                        goto fail;
                *modname++ = '\0';
                if ((export = strchr(modname, '\t')) != NULL)
                        *export++ = '\0';
                if (export && ((end = strchr(export, '\t')) != NULL))
                        *end = '\0';
                crc = strtoul(line, &d, 16);
                if (*symname == '\0' || *modname == '\0' || *d != '\0')
                        goto fail;

                if (!(mod = find_module(modname))) {
                        if (is_vmlinux(modname)) {
                                have_vmlinux = 1;
                        }
                        mod = new_module(NOFAIL(strdup(modname)));
                        mod->skip = 1;
                }
                s = sym_add_exported(symname, mod, export_no(export));
                s->kernel    = kernel;
                s->preloaded = 1;
                sym_update_crc(symname, mod, crc, export_no(export));
        }
        return;
fail:
        fatal("parse error in symbol dump file\n");
}

/* For normal builds always dump all symbols.
 * For external modules only dump symbols
 * that are not read from kernel Module.symvers.
 **/
static int dump_sym(struct symbol *sym)
{
        if (!external_module)
                return 1;
        if (sym->vmlinux || sym->kernel)
                return 0;
        return 1;
}

static void write_dump(const char *fname)
{
        struct buffer buf = { };
        struct symbol *symbol;
        int n;

        for (n = 0; n < SYMBOL_HASH_SIZE ; n++) {
                symbol = symbolhash[n];
                while (symbol) {
                        if (dump_sym(symbol))
                                buf_printf(&buf, "0x%08x\t%s\t%s\t%s\n",
                                        symbol->crc, symbol->name,
                                        symbol->module->name,
                                        export_str(symbol->export));
                        symbol = symbol->next;
                }
        }
        write_if_changed(&buf, fname);
}

int main(int argc, char **argv)
{
        struct module *mod;
        struct buffer buf = { };
        char fname[SZ];
        char *kernel_read = NULL, *module_read = NULL;
        char *dump_write = NULL;
        int opt;
        int err;

        while ((opt = getopt(argc, argv, "i:I:mo:aw")) != -1) {
                switch(opt) {
                        case 'i':
                                kernel_read = optarg;
                                break;
                        case 'I':
                                module_read = optarg;
                                external_module = 1;
                                break;
                        case 'm':
                                modversions = 1;
                                break;
                        case 'o':
                                dump_write = optarg;
                                break;
                        case 'a':
                                all_versions = 1;
                                break;
                        case 'w':
                                warn_unresolved = 1;
                                break;
                        default:
                                exit(1);
                }
        }

        if (kernel_read)
                read_dump(kernel_read, 1);
        if (module_read)
                read_dump(module_read, 0);

        while (optind < argc) {
                read_symbols(argv[optind++]);
        }

        for (mod = modules; mod; mod = mod->next) {
                if (mod->skip)
                        continue;
                check_exports(mod);
        }

        err = 0;

        for (mod = modules; mod; mod = mod->next) {
                if (mod->skip)
                        continue;

                buf.pos = 0;

                add_header(&buf, mod);
                err |= add_versions(&buf, mod);
                add_depends(&buf, mod, modules);
                add_moddevtable(&buf, mod);
                add_srcversion(&buf, mod);

                sprintf(fname, "%s.mod.c", mod->name);
                write_if_changed(&buf, fname);
        }

        if (dump_write)
                write_dump(dump_write);

        return err;
}