/*
 * "Optimize" a list of dependencies as spit out by gcc -MD
 * for the kernel build
 * ===========================================================================
 *
 * Author       Kai Germaschewski
 * Copyright    2002 by Kai Germaschewski  <kai.germaschewski@gmx.de>
 *
 * This software may be used and distributed according to the terms
 * of the GNU General Public License, incorporated herein by reference.
 *
 *
 * Introduction:
 *
 * gcc produces a very nice and correct list of dependencies which
 * tells make when to remake a file.
 *
 * To use this list as-is however has the drawback that virtually
 * every file in the kernel includes autoconf.h.
 *
 * If the user re-runs make *config, autoconf.h will be
 * regenerated.  make notices that and will rebuild every file which
 * includes autoconf.h, i.e. basically all files. This is extremely
 * annoying if the user just changed CONFIG_HIS_DRIVER from n to m.
 *
 * So we play the same trick that "mkdep" played before. We replace
 * the dependency on autoconf.h by a dependency on every config
 * option which is mentioned in any of the listed prerequisites.
 *
 * kconfig populates a tree in include/config/ with an empty file
 * for each config symbol and when the configuration is updated
 * the files representing changed config options are touched
 * which then let make pick up the changes and the files that use
 * the config symbols are rebuilt.
 *
 * So if the user changes his CONFIG_HIS_DRIVER option, only the objects
 * which depend on "include/config/his/driver.h" will be rebuilt,
 * so most likely only his driver ;-)
 *
 * The idea above dates, by the way, back to Michael E Chastain, AFAIK.
 *
 * So to get dependencies right, there are two issues:
 * o if any of the files the compiler read changed, we need to rebuild
 * o if the command line given to the compile the file changed, we
 *   better rebuild as well.
 *
 * The former is handled by using the -MD output, the later by saving
 * the command line used to compile the old object and comparing it
 * to the one we would now use.
 *
 * Again, also this idea is pretty old and has been discussed on
 * kbuild-devel a long time ago. I don't have a sensibly working
 * internet connection right now, so I rather don't mention names
 * without double checking.
 *
 * This code here has been based partially based on mkdep.c, which
 * says the following about its history:
 *
 *   Copyright abandoned, Michael Chastain, <mailto:mec@shout.net>.
 *   This is a C version of syncdep.pl by Werner Almesberger.
 *
 *
 * It is invoked as
 *
 *   fixdep <depfile> <target> <cmdline>
 *
 * and will read the dependency file <depfile>
 *
 * The transformed dependency snipped is written to stdout.
 *
 * It first generates a line
 *
 *   cmd_<target> = <cmdline>
 *
 * and then basically copies the .<target>.d file to stdout, in the
 * process filtering out the dependency on autoconf.h and adding
 * dependencies on include/config/my/option.h for every
 * CONFIG_MY_OPTION encountered in any of the prerequisites.
 *
 * It will also filter out all the dependencies on *.ver. We need
 * to make sure that the generated version checksum are globally up
 * to date before even starting the recursive build, so it's too late
 * at this point anyway.
 *
 * We don't even try to really parse the header files, but
 * merely grep, i.e. if CONFIG_FOO is mentioned in a comment, it will
 * be picked up as well. It's not a problem with respect to
 * correctness, since that can only give too many dependencies, thus
 * we cannot miss a rebuild. Since people tend to not mention totally
 * unrelated CONFIG_ options all over the place, it's not an
 * efficiency problem either.
 *
 * (Note: it'd be easy to port over the complete mkdep state machine,
 *  but I don't think the added complexity is worth it)
 */

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>

static void usage(void)
{
        fprintf(stderr, "Usage: fixdep <depfile> <target> <cmdline>\n");
        exit(1);
}

/*
 * Print out a dependency path from a symbol name
 */
static void print_dep(const char *m, int slen, const char *dir)
{
        int c, prev_c = '/', i;

        printf("    $(wildcard %s/", dir);
        for (i = 0; i < slen; i++) {
                c = m[i];
                if (c == '_')
                        c = '/';
                else
                        c = tolower(c);
                if (c != '/' || prev_c != '/')
                        putchar(c);
                prev_c = c;
        }
        printf(".h) \\\n");
}

struct item {
        struct item     *next;
        unsigned int    len;
        unsigned int    hash;
        char            name[0];
};

#define HASHSZ 256
static struct item *hashtab[HASHSZ];

static unsigned int strhash(const char *str, unsigned int sz)
{
        /* fnv32 hash */
        unsigned int i, hash = 2166136261U;

        for (i = 0; i < sz; i++)
                hash = (hash ^ str[i]) * 0x01000193;
        return hash;
}

/*
 * Lookup a value in the configuration string.
 */
static int is_defined_config(const char *name, int len, unsigned int hash)
{
        struct item *aux;

        for (aux = hashtab[hash % HASHSZ]; aux; aux = aux->next) {
                if (aux->hash == hash && aux->len == len &&
                    memcmp(aux->name, name, len) == 0)
                        return 1;
        }
        return 0;
}

/*
 * Add a new value to the configuration string.
 */
static void define_config(const char *name, int len, unsigned int hash)
{
        struct item *aux = malloc(sizeof(*aux) + len);

        if (!aux) {
                perror("fixdep:malloc");
                exit(1);
        }
        memcpy(aux->name, name, len);
        aux->len = len;
        aux->hash = hash;
        aux->next = hashtab[hash % HASHSZ];
        hashtab[hash % HASHSZ] = aux;
}

/*
 * Record the use of a CONFIG_* word.
 */
static void use_config(const char *m, int slen)
{
        unsigned int hash = strhash(m, slen);

        if (is_defined_config(m, slen, hash))
            return;

        define_config(m, slen, hash);
        print_dep(m, slen, "include/config");
}

/* test if s ends in sub */
static int str_ends_with(const char *s, int slen, const char *sub)
{
        int sublen = strlen(sub);

        if (sublen > slen)
                return 0;

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

static void parse_config_file(const char *p)
{
        const char *q, *r;
        const char *start = p;

        while ((p = strstr(p, "CONFIG_"))) {
                if (p > start && (isalnum(p[-1]) || p[-1] == '_')) {
                        p += 7;
                        continue;
                }
                p += 7;
                q = p;
                while (*q && (isalnum(*q) || *q == '_'))
                        q++;
                if (str_ends_with(p, q - p, "_MODULE"))
                        r = q - 7;
                else
                        r = q;
                if (r > p)
                        use_config(p, r - p);
                p = q;
        }
}

static void *read_file(const char *filename)
{
        struct stat st;
        int fd;
        char *buf;

        fd = open(filename, O_RDONLY);
        if (fd < 0) {
                fprintf(stderr, "fixdep: error opening file: ");
                perror(filename);
                exit(2);
        }
        if (fstat(fd, &st) < 0) {
                fprintf(stderr, "fixdep: error fstat'ing file: ");
                perror(filename);
                exit(2);
        }
        buf = malloc(st.st_size + 1);
        if (!buf) {
                perror("fixdep: malloc");
                exit(2);
        }
        if (read(fd, buf, st.st_size) != st.st_size) {
                perror("fixdep: read");
                exit(2);
        }
        buf[st.st_size] = '\0';
        close(fd);

        return buf;
}

/* Ignore certain dependencies */
static int is_ignored_file(const char *s, int len)
{
        return str_ends_with(s, len, "include/generated/autoconf.h") ||
               str_ends_with(s, len, "include/generated/autoksyms.h") ||
               str_ends_with(s, len, ".ver");
}

/*
 * Important: The below generated source_foo.o and deps_foo.o variable
 * assignments are parsed not only by make, but also by the rather simple
 * parser in scripts/mod/sumversion.c.
 */
static void parse_dep_file(char *m, const char *target)
{
        char *p;
        int is_last, is_target;
        int saw_any_target = 0;
        int is_first_dep = 0;
        void *buf;

        while (1) {
                /* Skip any "white space" */
                while (*m == ' ' || *m == '\\' || *m == '\n')
                        m++;

                if (!*m)
                        break;

                /* Find next "white space" */
                p = m;
                while (*p && *p != ' ' && *p != '\\' && *p != '\n')
                        p++;
                is_last = (*p == '\0');
                /* Is the token we found a target name? */
                is_target = (*(p-1) == ':');
                /* Don't write any target names into the dependency file */
                if (is_target) {
                        /* The /next/ file is the first dependency */
                        is_first_dep = 1;
                } else if (!is_ignored_file(m, p - m)) {
                        *p = '\0';

                        /*
                         * Do not list the source file as dependency, so that
                         * kbuild is not confused if a .c file is rewritten
                         * into .S or vice versa. Storing it in source_* is
                         * needed for modpost to compute srcversions.
                         */
                        if (is_first_dep) {
                                /*
                                 * If processing the concatenation of multiple
                                 * dependency files, only process the first
                                 * target name, which will be the original
                                 * source name, and ignore any other target
                                 * names, which will be intermediate temporary
                                 * files.
                                 */
                                if (!saw_any_target) {
                                        saw_any_target = 1;
                                        printf("source_%s := %s\n\n",
                                               target, m);
                                        printf("deps_%s := \\\n", target);
                                }
                                is_first_dep = 0;
                        } else {
                                printf("  %s \\\n", m);
                        }

                        buf = read_file(m);
                        parse_config_file(buf);
                        free(buf);
                }

                if (is_last)
                        break;

                /*
                 * Start searching for next token immediately after the first
                 * "whitespace" character that follows this token.
                 */
                m = p + 1;
        }

        if (!saw_any_target) {
                fprintf(stderr, "fixdep: parse error; no targets found\n");
                exit(1);
        }

        printf("\n%s: $(deps_%s)\n\n", target, target);
        printf("$(deps_%s):\n", target);
}

int main(int argc, char *argv[])
{
        const char *depfile, *target, *cmdline;
        void *buf;

        if (argc != 4)
                usage();

        depfile = argv[1];
        target = argv[2];
        cmdline = argv[3];

        printf("cmd_%s := %s\n\n", target, cmdline);

        buf = read_file(depfile);
        parse_dep_file(buf, target);
        free(buf);

        return 0;
}