libbb: auto_string() for efficient handling of temporary malloced stirngs

Use it in libiproute: get rid of one static string buffer.

function                                             old     new   delta
auto_string                                            -      51     +51
ll_index_to_name                                      10      49     +39
buffer_fill_and_print                                169     178      +9
scan_recursive                                       378     380      +2
decode_one_format                                    732     734      +2
cmdputs                                              334     332      -2
static.cur_saved                                       4       1      -3
static.nbuf                                           16       -     -16
printable_string                                      94      57     -37
ll_idx_n2a                                            53       -     -53
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 4/3 up/down: 103/-111)           Total: -8 bytes
   text	   data	    bss	    dec	    hex	filename
 939880	    992	  17496	 958368	  e9fa0	busybox_old
 939880	    992	  17480	 958352	  e9f90	busybox_unstripped

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

include/libbb.h

@@ -692,6 +692,7 @@ int bb_putchar(int ch) FAST_FUNC;
 /* Note: does not use stdio, writes to fd 2 directly */
 int bb_putchar_stderr(char ch) FAST_FUNC;
 char *xasprintf(const char *format, ...) __attribute__ ((format(printf, 1, 2))) FAST_FUNC RETURNS_MALLOC;
+char *auto_string(char *str) FAST_FUNC;
 // gcc-4.1.1 still isn't good enough at optimizing it
 // (+200 bytes compared to macro)
 //static ALWAYS_INLINE

libbb/auto_string.c

@@ -0,0 +1,23 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2015 Denys Vlasenko
+ *
+ * Licensed under GPLv2, see file LICENSE in this source tree.
+ */
+//kbuild:lib-y += auto_string.o
+
+#include "libbb.h"
+
+char* FAST_FUNC auto_string(char *str)
+{
+	static char *saved[4];
+	static uint8_t cur_saved; /* = 0 */
+
+	free(saved[cur_saved]);
+	saved[cur_saved] = str;
+	cur_saved = (cur_saved + 1) & (ARRAY_SIZE(saved)-1);
+
+	return str;
+}

libbb/printable_string.c

@@ -11,9 +11,6 @@
 
 const char* FAST_FUNC printable_string(uni_stat_t *stats, const char *str)
 {
-	static char *saved[4];
-	static unsigned cur_saved; /* = 0 */
-
 	char *dst;
 	const char *s;
 
@@ -56,10 +53,5 @@ const char* FAST_FUNC printable_string(uni_stat_t *stats, const char *str)
 		}
 	}
 #endif
-
-	free(saved[cur_saved]);
-	saved[cur_saved] = dst;
-	cur_saved = (cur_saved + 1) & (ARRAY_SIZE(saved)-1);
-
-	return dst;
+	return auto_string(dst);
 }

networking/libiproute/ll_map.c

@@ -86,7 +86,8 @@ int FAST_FUNC ll_remember_index(const struct sockaddr_nl *who UNUSED_PARAM,
 	return 0;
 }
 
-const char FAST_FUNC *ll_idx_n2a(int idx, char *buf)
+static
+const char FAST_FUNC *ll_idx_n2a(int idx/*, char *buf*/)
 {
 	struct idxmap *im;
 
@@ -95,15 +96,15 @@ const char FAST_FUNC *ll_idx_n2a(int idx, char *buf)
 	im = find_by_index(idx);
 	if (im)
 		return im->name;
-	snprintf(buf, 16, "if%d", idx);
-	return buf;
+	//snprintf(buf, 16, "if%d", idx);
+	//return buf;
+	return auto_string(xasprintf("if%d", idx));
 }
 
 const char FAST_FUNC *ll_index_to_name(int idx)
 {
-	static char nbuf[16];
-
-	return ll_idx_n2a(idx, nbuf);
+	//static char nbuf[16];
+	return ll_idx_n2a(idx/*, nbuf*/);
 }
 
 #ifdef UNUSED

networking/libiproute/ll_map.h

@@ -7,8 +7,8 @@ PUSH_AND_SET_FUNCTION_VISIBILITY_TO_HIDDEN
 int ll_remember_index(const struct sockaddr_nl *who, struct nlmsghdr *n, void *arg) FAST_FUNC;
 int ll_init_map(struct rtnl_handle *rth) FAST_FUNC;
 int xll_name_to_index(const char *name) FAST_FUNC;
+//static: const char *ll_idx_n2a(int idx, char *buf) FAST_FUNC;
 const char *ll_index_to_name(int idx) FAST_FUNC;
-const char *ll_idx_n2a(int idx, char *buf) FAST_FUNC;
 /* int ll_index_to_type(int idx); */
 unsigned ll_index_to_flags(int idx) FAST_FUNC;