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>
This commit is contained in:
Ron Yorston
committed by
Denys Vlasenko
Denys Vlasenko
parent
9844d7e830
commit
610c4c385b
@@ -139,36 +139,56 @@ void FAST_FUNC bb_show_usage(void)
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xfunc_die();
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}
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#if NUM_APPLETS > 8
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static int applet_name_compare(const void *name, const void *idx)
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{
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int i = (int)(ptrdiff_t)idx - 1;
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return strcmp(name, APPLET_NAME(i));
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}
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#endif
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int FAST_FUNC find_applet_by_name(const char *name)
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{
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#if NUM_APPLETS > 8
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/* Do a binary search to find the applet entry given the name. */
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unsigned i, max;
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int j;
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const char *p;
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p = bsearch(name, (void*)(ptrdiff_t)1, ARRAY_SIZE(applet_main), 1, applet_name_compare);
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/*
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* if (!p) return -1;
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* ^^^^^^^^^^^^^^^^^^ the code below will do this if p == NULL :)
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*/
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return (int)(ptrdiff_t)p - 1;
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p = applet_names;
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i = 0;
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#if KNOWN_APPNAME_OFFSETS <= 0
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max = NUM_APPLETS;
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#else
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/* A version which does not pull in bsearch */
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int i = 0;
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const char *p = applet_names;
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while (i < NUM_APPLETS) {
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if (strcmp(name, p) == 0)
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return i;
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p += strlen(p) + 1;
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max = NUM_APPLETS * KNOWN_APPNAME_OFFSETS;
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for (j = ARRAY_SIZE(applet_nameofs)-1; j >= 0; j--) {
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const char *pp = applet_names + applet_nameofs[j];
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if (strcmp(name, pp) >= 0) {
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//bb_error_msg("name:'%s' >= pp:'%s'", name, pp);
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p = pp;
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i = max - NUM_APPLETS;
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break;
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}
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max -= NUM_APPLETS;
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}
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max /= (unsigned)KNOWN_APPNAME_OFFSETS;
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i /= (unsigned)KNOWN_APPNAME_OFFSETS;
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//bb_error_msg("name:'%s' starting from:'%s' i:%u max:%u", name, p, i, max);
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#endif
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/* Open-coding without strcmp/strlen calls for speed */
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while (i < max) {
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char ch;
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j = 0;
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/* Do we see "name\0" in applet_names[p] position? */
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while ((ch = *p) == name[j]) {
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if (ch == '\0') {
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//bb_error_msg("found:'%s' i:%u", name, i);
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return i; /* yes */
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}
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p++;
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j++;
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}
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/* No.
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* p => 1st non-matching char in applet_names[],
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* skip to and including NUL.
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*/
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while (ch != '\0')
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ch = *++p;
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p++;
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i++;
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}
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return -1;
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#endif
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}
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@@ -583,6 +603,7 @@ static void install_links(const char *busybox, int use_symbolic_links,
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* busybox.h::bb_install_loc_t, or else... */
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int (*lf)(const char *, const char *);
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char *fpc;
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const char *appname = applet_names;
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unsigned i;
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int rc;
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@@ -593,7 +614,7 @@ static void install_links(const char *busybox, int use_symbolic_links,
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for (i = 0; i < ARRAY_SIZE(applet_main); i++) {
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fpc = concat_path_file(
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custom_install_dir ? custom_install_dir : install_dir[APPLET_INSTALL_LOC(i)],
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APPLET_NAME(i));
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appname);
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// debug: bb_error_msg("%slinking %s to busybox",
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// use_symbolic_links ? "sym" : "", fpc);
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rc = lf(busybox, fpc);
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@@ -601,6 +622,8 @@ static void install_links(const char *busybox, int use_symbolic_links,
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bb_simple_perror_msg(fpc);
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}
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free(fpc);
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while (*appname++ != '\0')
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continue;
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}
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}
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# else
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@@ -754,7 +777,7 @@ void FAST_FUNC run_applet_no_and_exit(int applet_no, char **argv)
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/* Reinit some shared global data */
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xfunc_error_retval = EXIT_FAILURE;
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applet_name = APPLET_NAME(applet_no);
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applet_name = bb_get_last_path_component_nostrip(argv[0]);
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/* Special case. POSIX says "test --help"
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* should be no different from e.g. "test --foo".
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@@ -785,11 +808,14 @@ void FAST_FUNC run_applet_no_and_exit(int applet_no, char **argv)
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void FAST_FUNC run_applet_and_exit(const char *name, char **argv)
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{
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int applet = find_applet_by_name(name);
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if (applet >= 0)
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run_applet_no_and_exit(applet, argv);
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int applet;
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if (is_prefixed_with(name, "busybox"))
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exit(busybox_main(argv));
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/* find_applet_by_name() search is more expensive, so goes second */
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applet = find_applet_by_name(name);
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if (applet >= 0)
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run_applet_no_and_exit(applet, argv);
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}
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#endif /* !defined(SINGLE_APPLET_MAIN) */
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