applet_tables: save space by removing applet name offsets

The array applet_nameofs consumes two bytes per applet.  It encodes

   nofork/noexec flags
   suid flags
   the offset of the applet name in the applet_name string

Change the applet_table build tool to store the flags in two separate
arrays (applet_flags and applet_suid).  Replace applet_nameofs[] with a
smaller version that only stores a limited number of offsets.

This requires changes to the macros APPLET_IS_NOFORK, APPLET_IS_NOEXEC
and APPLET_SUID.

   According to Valgrind the original find_applet_by_name required
   353 cycles per call, averaged over all names.  Adjusting the number
   of known offsets allows space to be traded off against execution time:

      KNOWN_OFFSETS     cycles     bytes (wrt KNOWN_OFFSETS = 0)

           0             9057        -
           2             4604       32
           4             2407       75
           8             1342       98
          16              908      130
          32              884      194

   This patch uses KNOWN_OFFSETS = 8.

v2:
   Remove some dead code from the applet_table tool;
   Treat the applet in the middle of the table as a special case.

v3:
   Use the middle applet to adjust the start of the linear search as
   well as the last applet found.

v4:
   Use an augmented linear search in find_applet_by_name.
   Drop the special treatment of the middle name from get_applet_name:
   most of the advantage now derives from the last stored value.

v5:
   Don't store index in applet_nameofs, it can be calculated.

v6:
   Tweaks by Denys

function                                             old     new   delta
find_applet_by_name                                   25     125    +100
applet_suid                                            -      92     +92
run_applet_no_and_exit                               452     460      +8
run_applet_and_exit                                  695     697      +2
applet_name_compare                                   31       -     -31
applet_nameofs                                       734      14    -720
------------------------------------------------------------------------------
(add/remove: 1/1 grow/shrink: 3/1 up/down: 202/-751)         Total: -549 bytes
   text       data        bss        dec        hex    filename
 925464        906      17160     943530      e65aa    busybox_old
 924915        906      17160     942981      e6385    busybox_unstripped

Signed-off-by: Ron Yorston <rmy@pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 54 insertions, 28 deletions

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 95e589e74..aeaf238f1 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -139,36 +139,56 @@ void FAST_FUNC bb_show_usage(void)
         xfunc_die();
 }
 
-#if NUM_APPLETS > 8
-static int applet_name_compare(const void *name, const void *idx)
-{
-        int i = (int)(ptrdiff_t)idx - 1;
-        return strcmp(name, APPLET_NAME(i));
-}
-#endif
 int FAST_FUNC find_applet_by_name(const char *name)
 {
-#if NUM_APPLETS > 8
-        /* Do a binary search to find the applet entry given the name. */
+        unsigned i, max;
+        int j;
         const char *p;
-        p = bsearch(name, (void*)(ptrdiff_t)1, ARRAY_SIZE(applet_main), 1, applet_name_compare);
-        /*
-         * if (!p) return -1;
-         * ^^^^^^^^^^^^^^^^^^ the code below will do this if p == NULL :)
-         */
-        return (int)(ptrdiff_t)p - 1;
+
+        p = applet_names;
+        i = 0;
+#if KNOWN_APPNAME_OFFSETS <= 0
+        max = NUM_APPLETS;
 #else
-        /* A version which does not pull in bsearch */
-        int i = 0;
-        const char *p = applet_names;
-        while (i < NUM_APPLETS) {
-                if (strcmp(name, p) == 0)
-                        return i;
-                p += strlen(p) + 1;
+        max = NUM_APPLETS * KNOWN_APPNAME_OFFSETS;
+        for (j = ARRAY_SIZE(applet_nameofs)-1; j >= 0; j--) {
+                const char *pp = applet_names + applet_nameofs[j];
+                if (strcmp(name, pp) >= 0) {
+                        //bb_error_msg("name:'%s' >= pp:'%s'", name, pp);
+                        p = pp;
+                        i = max - NUM_APPLETS;
+                        break;
+                }
+                max -= NUM_APPLETS;
+        }
+        max /= (unsigned)KNOWN_APPNAME_OFFSETS;
+        i /= (unsigned)KNOWN_APPNAME_OFFSETS;
+        //bb_error_msg("name:'%s' starting from:'%s' i:%u max:%u", name, p, i, max);
+#endif
+
+        /* Open-coding without strcmp/strlen calls for speed */
+        while (i < max) {
+                char ch;
+                j = 0;
+                /* Do we see "name\0" in applet_names[p] position? */
+                while ((ch = *p) == name[j]) {
+                        if (ch == '\0') {
+                                //bb_error_msg("found:'%s' i:%u", name, i);
+                                return i; /* yes */
+                        }
+                        p++;
+                        j++;
+                }
+                /* No.
+                 * p => 1st non-matching char in applet_names[],
+                 * skip to and including NUL.
+                 */
+                while (ch != '\0')
+                        ch = *++p;
+                p++;
                 i++;
         }
         return -1;
-#endif
 }
 
 
@@ -583,6 +603,7 @@ static void install_links(const char *busybox, int use_symbolic_links,
          * busybox.h::bb_install_loc_t, or else... */
         int (*lf)(const char *, const char *);
         char *fpc;
+        const char *appname = applet_names;
         unsigned i;
         int rc;
 
@@ -593,7 +614,7 @@ static void install_links(const char *busybox, int use_symbolic_links,
         for (i = 0; i < ARRAY_SIZE(applet_main); i++) {
                 fpc = concat_path_file(
                                 custom_install_dir ? custom_install_dir : install_dir[APPLET_INSTALL_LOC(i)],
-                                APPLET_NAME(i));
+                                appname);
                 // debug: bb_error_msg("%slinking %s to busybox",
                 //              use_symbolic_links ? "sym" : "", fpc);
                 rc = lf(busybox, fpc);
@@ -601,6 +622,8 @@ static void install_links(const char *busybox, int use_symbolic_links,
                         bb_simple_perror_msg(fpc);
                 }
                 free(fpc);
+                while (*appname++ != '\0')
+                        continue;
         }
 }
 # else
@@ -754,7 +777,7 @@ void FAST_FUNC run_applet_no_and_exit(int applet_no, char **argv)
 
         /* Reinit some shared global data */
         xfunc_error_retval = EXIT_FAILURE;
-        applet_name = APPLET_NAME(applet_no);
+        applet_name = bb_get_last_path_component_nostrip(argv[0]);
 
         /* Special case. POSIX says "test --help"
          * should be no different from e.g. "test --foo".
@@ -785,11 +808,14 @@ void FAST_FUNC run_applet_no_and_exit(int applet_no, char **argv)
 
 void FAST_FUNC run_applet_and_exit(const char *name, char **argv)
 {
-        int applet = find_applet_by_name(name);
-        if (applet >= 0)
-                run_applet_no_and_exit(applet, argv);
+        int applet;
+
         if (is_prefixed_with(name, "busybox"))
                 exit(busybox_main(argv));
+        /* find_applet_by_name() search is more expensive, so goes second */
+        applet = find_applet_by_name(name);
+        if (applet >= 0)
+                run_applet_no_and_exit(applet, argv);
 }
 
 #endif /* !defined(SINGLE_APPLET_MAIN) */