From 610c4c385b38280c7bde7a48d95ec019cbfe1ab4 Mon Sep 17 00:00:00 2001 From: Ron Yorston Date: Wed, 30 Mar 2016 00:42:05 +0200 Subject: 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 Signed-off-by: Denys Vlasenko --- applets/applet_tables.c | 78 +++++++++++++++++++++++++++++++++++++------------ 1 file changed, 60 insertions(+), 18 deletions(-) (limited to 'applets') diff --git a/applets/applet_tables.c b/applets/applet_tables.c index 92bf1e447..48544f08d 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"); -- cgit v1.2.3