On Tue, Aug 23, 2016 at 09:47:24PM +0300, Alexey Dobriyan wrote:
> Do you think kernel build is 100% dominated by gcc? You are wrong!
> One small utility called "fixdep" consistently manages to sneak into
> profile's first page (unless you have small monitor of course).
>
> The choke point is this clever code:
>
> 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; }
>
> 4 branches per 4 characters is not fast.
>
> Use strstr(3), so that SSE2 etc can be used.
>
> With this patch, fixdep is so deep at the bottom, it is hard to find it.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx>
> ---
>
> scripts/basic/fixdep.c | 67 ++++++++++++++++++++-----------------------------
> 1 file changed, 28 insertions(+), 39 deletions(-)
>
> --- a/scripts/basic/fixdep.c
> +++ b/scripts/basic/fixdep.c
> @@ -82,8 +82,7 @@
> * 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
> + * 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
> @@ -241,37 +240,22 @@ static void use_config(const char *m, int slen)
> print_config(m, slen);
> }
>
> -static void parse_config_file(const char *map, size_t len)
> +static void parse_config_file(const char *p)
> {
> - 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;
> + const char *q, *r;
> +
> + while ((p = strstr(p, "CONFIG_"))) {
> p += 7;
> - for (q = p; q < map + len; q++) {
> - if (!(isalnum(*q) || *q == '_'))
> - goto found;
> - }
> - continue;
> -
> - found:
> - if (!memcmp(q - 7, "_MODULE", 7))
> - q -= 7;
> - if (q - p < 0)
> - continue;
> - use_config(p, q - p);
> + q = p;
> + while (*q && (isalnum(*q) || *q == '_'))
> + q++;
> + if (memcmp(q - 7, "_MODULE", 7) == 0)
> + r = q - 7;
> + else
> + r = q;
> + if (r > p)
> + use_config(p, r - p);
> + p = q;
> }
> }
Faster and simpler - good.
>
> @@ -291,7 +275,7 @@ static void do_config_file(const char *filename)
> {
> struct stat st;
> int fd;
> - void *map;
> + char *map;
>
> fd = open(filename, O_RDONLY);
> if (fd < 0) {
> @@ -308,18 +292,23 @@ static void do_config_file(const char *filename)
> close(fd);
> return;
> }
> - map = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
> - if ((long) map == -1) {
> - perror("fixdep: mmap");
> + map = malloc(st.st_size + 1);
> + if (!map) {
> + perror("fixdep: malloc");
> close(fd);
> return;
> }
> + if (read(fd, map, st.st_size) != st.st_size) {
> + perror("fixdep: read");
> + close(fd);
> + return;
> + }
> + map[st.st_size] = '\0';
> + close(fd);
>
> - parse_config_file(map, st.st_size);
> -
> - munmap(map, st.st_size);
> + parse_config_file(map);
>
> - close(fd);
> + free(map);
> }
This change is not described in the changelog..
What is the rationale?
Sam
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