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>
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index 95e589e..aeaf238 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -139,36 +139,56 @@
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 @@
* 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 @@
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 @@
bb_simple_perror_msg(fpc);
}
free(fpc);
+ while (*appname++ != '\0')
+ continue;
}
}
# else
@@ -754,7 +777,7 @@
/* 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_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) */