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applet_tables: save space by removing applet name offsets

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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 2016-03-30 00:42:05 +02:00 committed by Denys Vlasenko
parent 9844d7e830
commit 610c4c385b
4 changed files with 122 additions and 60 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

82
applets/applet_tables.c
View File

@ -41,8 +41,6 @@ struct bb_applet {
enum { NUM_APPLETS = ARRAY_SIZE(applets) };
static int offset[NUM_APPLETS];
static int cmp_name(const void *a, const void *b)
{
const struct bb_applet *aa = a;
@ -60,22 +58,37 @@ static int str_isalnum_(const char *s)
return 1;
}
// Before linear search, narrow it down by looking at N "equidistant" names:
// KNOWN_APPNAME_OFFSETS cycles code_size
// 0 9057
// 2 4604 +32
// 4 2407 +75
// 8 1342 +98
// 16 908 +130
// 32 884 +194
// With 8, applet_nameofs[] table has 7 elements.
#define KNOWN_APPNAME_OFFSETS 8
int main(int argc, char **argv)
{
int i;
int ofs;
int i, j;
int ofs, offset[KNOWN_APPNAME_OFFSETS], index[KNOWN_APPNAME_OFFSETS];
// unsigned MAX_APPLET_NAME_LEN = 1;
qsort(applets, NUM_APPLETS, sizeof(applets[0]), cmp_name);
for (i = 0; i < KNOWN_APPNAME_OFFSETS; i++)
index[i] = i * NUM_APPLETS / KNOWN_APPNAME_OFFSETS;
ofs = 0;
for (i = 0; i < NUM_APPLETS; i++) {
offset[i] = ofs;
for (j = 0; j < KNOWN_APPNAME_OFFSETS; j++)
if (i == index[j])
offset[j] = ofs;
ofs += strlen(applets[i].name) + 1;
}
/* We reuse 4 high-order bits of offset array for other purposes,
* so if they are indeed needed, refuse to proceed */
if (ofs > 0xfff)
/* If the list of names is too long refuse to proceed */
if (ofs > 0xffff)
return 1;
if (!argv[1])
return 1;
@ -94,7 +107,17 @@ int main(int argc, char **argv)
printf("#define SINGLE_APPLET_STR \"%s\"\n", applets[0].name);
printf("#define SINGLE_APPLET_MAIN %s_main\n", applets[0].main);
}
printf("\n");
if (KNOWN_APPNAME_OFFSETS > 0 && NUM_APPLETS > 2*KNOWN_APPNAME_OFFSETS) {
printf("#define KNOWN_APPNAME_OFFSETS %u\n\n", KNOWN_APPNAME_OFFSETS);
printf("const uint16_t applet_nameofs[] ALIGN2 = {\n");
for (i = 1; i < KNOWN_APPNAME_OFFSETS; i++)
printf("%d,\n", offset[i]);
printf("};\n\n");
}
else {
printf("#define KNOWN_APPNAME_OFFSETS 0\n\n");
}
//printf("#ifndef SKIP_definitions\n");
printf("const char applet_names[] ALIGN1 = \"\"\n");
@ -119,20 +142,39 @@ int main(int argc, char **argv)
printf("};\n");
printf("#endif\n\n");
printf("const uint16_t applet_nameofs[] ALIGN2 = {\n");
for (i = 0; i < NUM_APPLETS; i++) {
printf("0x%04x,\n",
offset[i]
#if ENABLE_FEATURE_PREFER_APPLETS
+ (applets[i].nofork << 12)
+ (applets[i].noexec << 13)
#endif
#if ENABLE_FEATURE_SUID
+ (applets[i].need_suid << 14) /* 2 bits */
#endif
);
printf("const uint8_t applet_flags[] ALIGN1 = {\n");
i = 0;
while (i < NUM_APPLETS) {
int v = applets[i].nofork + (applets[i].noexec << 1);
if (++i < NUM_APPLETS)
v |= (applets[i].nofork + (applets[i].noexec << 1)) << 2;
if (++i < NUM_APPLETS)
v |= (applets[i].nofork + (applets[i].noexec << 1)) << 4;
if (++i < NUM_APPLETS)
v |= (applets[i].nofork + (applets[i].noexec << 1)) << 6;
printf("0x%02x,\n", v);
i++;
}
printf("};\n\n");
#endif
#if ENABLE_FEATURE_SUID
printf("const uint8_t applet_suid[] ALIGN1 = {\n");
i = 0;
while (i < NUM_APPLETS) {
int v = applets[i].need_suid; /* 2 bits */
if (++i < NUM_APPLETS)
v |= applets[i].need_suid << 2;
if (++i < NUM_APPLETS)
v |= applets[i].need_suid << 4;
if (++i < NUM_APPLETS)
v |= applets[i].need_suid << 6;
printf("0x%02x,\n", v);
i++;
}
printf("};\n\n");
#endif
#if ENABLE_FEATURE_INSTALLER
printf("const uint8_t applet_install_loc[] ALIGN1 = {\n");

15
include/busybox.h
View File

@ -15,25 +15,20 @@ PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
/* Keep in sync with applets/applet_tables.c! */
extern const char applet_names[] ALIGN1;
extern int (*const applet_main[])(int argc, char **argv);
extern const uint16_t applet_nameofs[];
extern const uint8_t applet_flags[] ALIGN1;
extern const uint8_t applet_suid[] ALIGN1;
extern const uint8_t applet_install_loc[] ALIGN1;
#if ENABLE_FEATURE_SUID || ENABLE_FEATURE_PREFER_APPLETS
# define APPLET_NAME(i) (applet_names + (applet_nameofs[i] & 0x0fff))
#else
# define APPLET_NAME(i) (applet_names + applet_nameofs[i])
#endif
#if ENABLE_FEATURE_PREFER_APPLETS
# define APPLET_IS_NOFORK(i) (applet_nameofs[i] & (1 << 12))
# define APPLET_IS_NOEXEC(i) (applet_nameofs[i] & (1 << 13))
# define APPLET_IS_NOFORK(i) (applet_flags[(i)/4] & (1 << (2 * ((i)%4))))
# define APPLET_IS_NOEXEC(i) (applet_flags[(i)/4] & (1 << ((2 * ((i)%4))+1)))
#else
# define APPLET_IS_NOFORK(i) 0
# define APPLET_IS_NOEXEC(i) 0
#endif
#if ENABLE_FEATURE_SUID
# define APPLET_SUID(i) ((applet_nameofs[i] >> 14) & 0x3)
# define APPLET_SUID(i) ((applet_suid[(i)/4] >> (2 * ((i)%4)) & 3))
#endif
#if ENABLE_FEATURE_INSTALLER

82
libbb/appletlib.c
View File

@ -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) */

3
libbb/vfork_daemon_rexec.c
View File

@ -116,8 +116,6 @@ int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
save_nofork_data(&old);
applet_name = APPLET_NAME(applet_no);
xfunc_error_retval = EXIT_FAILURE;
/* In case getopt() or getopt32() was already called:
@ -157,6 +155,7 @@ int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
* need argv untouched because they free argv[i]! */
char *tmp_argv[argc+1];
memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
applet_name = tmp_argv[0];
/* Finally we can call NOFORK applet's main() */
rc = applet_main[applet_no](argc, tmp_argv);
} else {