[git commit] applet_tables: save space by removing applet name offsets
Denys Vlasenko
vda.linux at googlemail.com
Tue Mar 29 22:44:11 UTC 2016
commit: https://git.busybox.net/busybox/commit/?id=610c4c385b38280c7bde7a48d95ec019cbfe1ab4
branch: https://git.busybox.net/busybox/commit/?id=refs/heads/master
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 at pobox.com>
Signed-off-by: Denys Vlasenko <vda.linux at googlemail.com>
---
applets/applet_tables.c | 78 +++++++++++++++++++++++++++++++++----------
include/busybox.h | 15 +++------
libbb/appletlib.c | 82 ++++++++++++++++++++++++++++++----------------
libbb/vfork_daemon_rexec.c | 3 +-
4 files changed, 120 insertions(+), 58 deletions(-)
diff --git a/applets/applet_tables.c b/applets/applet_tables.c
index 92bf1e4..48544f0 100644
--- a/applets/applet_tables.c
+++ b/applets/applet_tables.c
@@ -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)
+ 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
- + (applets[i].need_suid << 14) /* 2 bits */
-#endif
- );
+ 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");
diff --git a/include/busybox.h b/include/busybox.h
index b1e31e5..737627b 100644
--- a/include/busybox.h
+++ b/include/busybox.h
@@ -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
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 @@ 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) */
diff --git a/libbb/vfork_daemon_rexec.c b/libbb/vfork_daemon_rexec.c
index d6ca7b2..1adb5b3 100644
--- a/libbb/vfork_daemon_rexec.c
+++ b/libbb/vfork_daemon_rexec.c
@@ -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 {
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