stdio: implement assignment-allocation "m" character

The latest POSIX spec introduces a "m" character to allocate buffers for
the user when using scanf type functions.  This is like the old glibc "a"
flag, but now standardized.  With packages starting to use these, we need
to implement it.

for example:
	char *s;
	sscanf("foo", "%ms", &s);
	printf("%s\n", s);
	free(s);
This will automatically allocate storage for "s", read in "foo" to it,
and then display it.

I'm not terribly familiar with the stdio layer, so this could be wrong.
But it seems to work for me.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

extra/Configs/Config.in

@@ -1590,19 +1590,6 @@ config UCLIBC_PRINTF_SCANF_POSITIONAL_ARGS
 
 	  Most people will answer 9.
 
-
-config UCLIBC_HAS_SCANF_GLIBC_A_FLAG
-	bool "Support glibc's 'a' flag for scanf string conversions (not implemented)"
-	help
-	  NOTE!!!  Currently Not Implemented!!! Just A Place Holder!!  NOTE!!!
-	  NOTE!!!  Conflicts with an ANSI/ISO C99 scanf flag!!         NOTE!!!
-
-	  Answer Y to enable support for glibc's 'a' flag for the scanf string
-	  conversions '%s', '%[', '%ls', '%l[', and '%S'.  This is used to
-	  auto-allocate sufficient memory to hold the data retrieved.
-
-	  Most people will answer N.
-
 choice
 	prompt "Stdio buffer size"
 	default UCLIBC_HAS_STDIO_BUFSIZ_4096

libc/stdio/_scanf.c

@@ -77,14 +77,6 @@
 #include <bits/uClibc_fpmax.h>
 #endif /* __UCLIBC_HAS_FLOATS__ */
 
-#ifdef __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__
-#ifdef L_vfscanf
-/* only emit this once */
-#warning Forcing undef of __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__ until implemented!
-#endif
-#undef __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__
-#endif
-
 #undef __STDIO_HAS_VSSCANF
 #if defined(__STDIO_BUFFERS) || !defined(__UCLIBC_HAS_WCHAR__) || defined(__UCLIBC_HAS_GLIBC_CUSTOM_STREAMS__)
 #define __STDIO_HAS_VSSCANF 1
@@ -433,8 +425,9 @@ libc_hidden_def(vswscanf)
 
 
 /* float layout          0123456789012345678901  repeat n for "l[" */
-#define SPEC_CHARS		"npxXoudifFeEgGaACSncs["
-/*                       npxXoudif eEgG  CS cs[ */
+#define SPEC_CHARS		"npxXoudifFeEgGaACSnmcs["
+/*                       npxXoudif eEgG  CS  cs[ */
+/* NOTE: the 'm' flag must come before any convs that support it */
 
 /* NOTE: Ordering is important!  In particular, CONV_LEFTBRACKET
  * must immediately precede CONV_c. */
@@ -444,7 +437,7 @@ enum {
 	CONV_p,
 	CONV_x, CONV_X,	CONV_o,	CONV_u,	CONV_d,	CONV_i,
 	CONV_f, CONV_F, CONV_e, CONV_E, CONV_g, CONV_G, CONV_a, CONV_A,
-	CONV_C, CONV_S, CONV_LEFTBRACKET, CONV_c, CONV_s, CONV_leftbracket,
+	CONV_C, CONV_S, CONV_LEFTBRACKET, CONV_m, CONV_c, CONV_s, CONV_leftbracket,
 	CONV_percent, CONV_whitespace /* not in SPEC_* and no flags */
 };
 
@@ -474,7 +467,7 @@ enum {
 	FLAG_SURPRESS   =   0x10,	/* MUST BE 1ST!!  See DO_FLAGS. */
 	FLAG_THOUSANDS	=	0x20,
 	FLAG_I18N		=	0x40,	/* only works for d, i, u */
-	FLAG_MALLOC     =   0x80,	/* only works for s, S, and [ (and l[)*/
+	FLAG_MALLOC     =   0x80,	/* only works for c, s, S, and [ (and l[)*/
 };
 
 
@@ -491,7 +484,7 @@ enum {
 	/* fFeEgGaA */	(0x0c|FLAG_SURPRESS|FLAG_THOUSANDS|FLAG_I18N), \
 	/* C */			(   0|FLAG_SURPRESS), \
 	/* S and l[ */	(   0|FLAG_SURPRESS|FLAG_MALLOC), \
-	/* c */			(0x04|FLAG_SURPRESS), \
+	/* c */			(0x04|FLAG_SURPRESS|FLAG_MALLOC), \
 	/* s and [ */	(0x04|FLAG_SURPRESS|FLAG_MALLOC), \
 }
 
@@ -904,17 +897,17 @@ int attribute_hidden __psfs_parse_spec(register psfs_t *psfs)
 		if (*psfs->fmt == *p) {
 			int p_m_spec_chars = p - spec_chars;
 
-#ifdef __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__
-#error implement gnu a flag
-			if ((*p == 'a')
-				&& ((psfs->fmt[1] == '[') || ((psfs->fmt[1]|0x20) == 's'))
-				) {		/* Assumes ascii for 's' and 'S' test. */
-				psfs->flags |= FLAG_MALLOC;
+			if (*p == 'm' &&
+				(psfs->fmt[1] == '[' || psfs->fmt[1] == 'c' ||
+				 /* Assumes ascii for 's' and 'S' test. */
+				 (psfs->fmt[1] | 0x20) == 's'))
+			{
+				if (psfs->store)
+					psfs->flags |= FLAG_MALLOC;
 				++psfs->fmt;
 				++p;
-				continue; /* The related conversions follow 'a'. */
+				continue; /* The related conversions follow 'm'. */
 			}
-#endif /* __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__ */
 
 			for (p = spec_ranges; p_m_spec_chars > *p ; ++p) {}
 			if (((psfs->dataargtype >> 8) | psfs->flags)
@@ -1265,12 +1258,6 @@ int VFSCANF (FILE *__restrict fp, const Wchar *__restrict format, va_list arg)
 				while (*wf && __isascii(*wf) && (b < buf + sizeof(buf) - 1)) {
 					*b++ = *wf++;
 				}
-#ifdef __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__
-#error this is wrong... we need to ched in __psfs_parse_spec instead since this checks last char in buffer and conversion my have stopped before it.
-				if ((*b == 'a') && ((*wf == '[') || ((*wf|0x20) == 's'))) {
-					goto DONE;	/* Spec was excessively long. */
-				}
-#endif /* __UCLIBC_HAS_SCANF_GLIBC_A_FLAG__ */
 				*b = 0;
 				if (b == buf) { /* Bad conversion specifier! */
 					goto DONE;
@@ -1390,13 +1377,36 @@ int VFSCANF (FILE *__restrict fp, const Wchar *__restrict format, va_list arg)
 				}
 
 				if (psfs.conv_num == CONV_s) {
+					/* We might have to handle the allocation ourselves */
+					int len;
+					/* With 'm', we actually got a pointer to a pointer */
+					unsigned char **ptr = (void *)b;
+
+					i = 0;
+					if (psfs.flags & FLAG_MALLOC) {
+						len = 0;
+						b = NULL;
+					} else
+						len = -1;
+
 					/* Yes, believe it or not, a %s conversion can store nuls. */
 					while ((__scan_getc(&sc) >= 0) && !isspace(sc.cc)) {
 						zero_conversions = 0;
-						*b = sc.cc;
-						b += psfs.store;
+						if (i == len) {
+							/* Pick a size that won't trigger a lot of
+							 * mallocs early on ... */
+							len += 256;
+							b = realloc(b, len + 1);
+						}
+						b[i] = sc.cc;
+						i += psfs.store;
 						fail = 0;
 					}
+
+					if (psfs.flags & FLAG_MALLOC)
+						*ptr = b;
+					/* The code below takes care of terminating NUL */
+					b += i;
 				} else {
 #ifdef __UCLIBC_HAS_WCHAR__
 					assert((psfs.conv_num == CONV_LEFTBRACKET) || \