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
@@ -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");
|
||||
|
||||
Reference in New Issue
Block a user