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