/*
   * "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 prequisites.
   *
   * 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/linux/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 prequisites.
   *
   * 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.
   *
   * The algorithm to grep for "CONFIG_..." is bit unusual, but should
   * be fast ;-) 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)
   */
  /*
   * Note 2: if somebody writes HELLO_CONFIG_BOOM in a file, it will depend onto
   * CONFIG_BOOM. This could seem a bug (not too hard to fix), but please do not
   * fix it! Some UserModeLinux files (look at arch/um/) call CONFIG_BOOM as
   * UML_CONFIG_BOOM, to avoid conflicts with /usr/include/linux/autoconf.h,
   * through arch/um/include/uml-config.h; this fixdep "bug" makes sure that
   * those files will have correct dependencies.
   */
  
  #include <sys/types.h>
  #include <sys/stat.h>
  #include <sys/mman.h>
  #include <unistd.h>
  #include <fcntl.h>
  #include <string.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <limits.h>
  #include <ctype.h>
  #include <arpa/inet.h>
  
  #define INT_CONF ntohl(0x434f4e46)
  #define INT_ONFI ntohl(0x4f4e4649)
  #define INT_NFIG ntohl(0x4e464947)
  #define INT_FIG_ ntohl(0x4649475f)
  
  char *target;
  char *depfile;
  char *cmdline;
  
  static void usage(void)
  {
  	fprintf(stderr, "Usage: fixdep <depfile> <target> <cmdline>
  ");
  	exit(1);
  }
  
  /*
   * Print out the commandline prefixed with cmd_<target filename> :=
   */
  static void print_cmdline(void)
  {
  	printf("cmd_%s := %s
  
  ", target, cmdline);
  }
  
  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;
  }
  
  /*
   * Clear the set of configuration strings.
   */
  static void clear_config(void)
  {
  	struct item *aux, *next;
  	unsigned int i;
  
  	for (i = 0; i < HASHSZ; i++) {
  		for (aux = hashtab[i]; aux; aux = next) {
  			next = aux->next;
  			free(aux);
  		}
  		hashtab[i] = NULL;
  	}
  }
  
  /*
   * Record the use of a CONFIG_* word.
   */
  static void use_config(const char *m, int slen)
  {
  	unsigned int hash = strhash(m, slen);
  	int c, i;
  
  	if (is_defined_config(m, slen, hash))
  	    return;
  
  	define_config(m, slen, hash);
  
  	printf("    $(wildcard include/config/");
  	for (i = 0; i < slen; i++) {
  		c = m[i];
  		if (c == '_')
  			c = '/';
  		else
  			c = tolower(c);
  		putchar(c);
  	}
  	printf(".h) \\
  ");
  }
  
  static void parse_config_file(const char *map, size_t len)
  {
  	const int *end = (const int *) (map + len);
  	/* start at +1, so that p can never be < map */
  	const int *m   = (const int *) map + 1;
  	const char *p, *q;
  
  	for (; m < end; m++) {
  		if (*m == INT_CONF) { p = (char *) m  ; goto conf; }
  		if (*m == INT_ONFI) { p = (char *) m-1; goto conf; }
  		if (*m == INT_NFIG) { p = (char *) m-2; goto conf; }
  		if (*m == INT_FIG_) { p = (char *) m-3; goto conf; }
  		continue;
  	conf:
  		if (p > map + len - 7)
  			continue;
  		if (memcmp(p, "CONFIG_", 7))
  			continue;
  		for (q = p + 7; q < map + len; q++) {
  			if (!(isalnum(*q) || *q == '_'))
  				goto found;
  		}
  		continue;
  
  	found:
  		if (!memcmp(q - 7, "_MODULE", 7))
  			q -= 7;
  		if( (q-p-7) < 0 )
  			continue;
  		use_config(p+7, q-p-7);
  	}
  }
  
  /* test is s ends in sub */
  static int strrcmp(char *s, char *sub)
  {
  	int slen = strlen(s);
  	int sublen = strlen(sub);
  
  	if (sublen > slen)
  		return 1;
  
  	return memcmp(s + slen - sublen, sub, sublen);
  }
  
  static void do_config_file(const char *filename)
  {
  	struct stat st;
  	int fd;
  	void *map;
  
  	fd = open(filename, O_RDONLY);
  	if (fd < 0) {
  		fprintf(stderr, "fixdep: error opening config file: ");
  		perror(filename);
  		exit(2);
  	}
  	fstat(fd, &st);
  	if (st.st_size == 0) {
  		close(fd);
  		return;
  	}
  	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
  	if ((long) map == -1) {
  		perror("fixdep: mmap");
  		close(fd);
  		return;
  	}
  
  	parse_config_file(map, st.st_size);
  
  	munmap(map, st.st_size);
  
  	close(fd);
  }
  
  /*
   * 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(void *map, size_t len)
  {
  	char *m = map;
  	char *end = m + len;
  	char *p;
  	char s[PATH_MAX];
  	int is_target;
  	int saw_any_target = 0;
  	int is_first_dep = 0;
  
  	clear_config();
  
  	while (m < end) {
  		/* Skip any "white space" */
  		while (m < end && (*m == ' ' || *m == '\\' || *m == '
  '))
  			m++;
  		/* Find next "white space" */
  		p = m;
  		while (p < end && *p != ' ' && *p != '\\' && *p != '
  ')
  			p++;
  		/* 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 {
  			/* Save this token/filename */
  			memcpy(s, m, p-m);
  			s[p - m] = 0;
  
  			/* Ignore certain dependencies */
  			if (strrcmp(s, "include/generated/autoconf.h") &&
  			    strrcmp(s, "arch/um/include/uml-config.h") &&
  			    strrcmp(s, "include/linux/kconfig.h") &&
  			    strrcmp(s, ".ver")) {
  				/*
  				 * 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
  
  ",
  							target, s);
  						printf("deps_%s := \\
  ",
  							target);
  					}
  					is_first_dep = 0;
  				} else
  					printf("  %s \\
  ", s);
  				do_config_file(s);
  			}
  		}
  		/*
  		 * 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
  ");
  		exit(1);
  	}
  
  	printf("
  %s: $(deps_%s)
  
  ", target, target);
  	printf("$(deps_%s):
  ", target);
  }
  
  static void print_deps(void)
  {
  	struct stat st;
  	int fd;
  	void *map;
  
  	fd = open(depfile, O_RDONLY);
  	if (fd < 0) {
  		fprintf(stderr, "fixdep: error opening depfile: ");
  		perror(depfile);
  		exit(2);
  	}
  	if (fstat(fd, &st) < 0) {
                  fprintf(stderr, "fixdep: error fstat'ing depfile: ");
                  perror(depfile);
                  exit(2);
          }
  	if (st.st_size == 0) {
  		fprintf(stderr,"fixdep: %s is empty
  ",depfile);
  		close(fd);
  		return;
  	}
  	map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
  	if ((long) map == -1) {
  		perror("fixdep: mmap");
  		close(fd);
  		return;
  	}
  
  	parse_dep_file(map, st.st_size);
  
  	munmap(map, st.st_size);
  
  	close(fd);
  }
  
  static void traps(void)
  {
  	static char test[] __attribute__((aligned(sizeof(int)))) = "CONF";
  	int *p = (int *)test;
  
  	if (*p != INT_CONF) {
  		fprintf(stderr, "fixdep: sizeof(int) != 4 or wrong endianness? %#x
  ",
  			*p);
  		exit(2);
  	}
  }
  
  int main(int argc, char *argv[])
  {
  	traps();
  
  	if (argc != 4)
  		usage();
  
  	depfile = argv[1];
  	target = argv[2];
  	cmdline = argv[3];
  
  	print_cmdline();
  	print_deps();
  
  	return 0;
  }