[PATCH V3] tiny-printf: Handle formatting of %p with an extra Kconfig

Christoph Niedermaier cniedermaier at dh-electronics.com
Wed Apr 30 12:35:48 CEST 2025 

The formatting with %pa / %pap behaves like %x, which results in an
incorrect value being output. To improve this, a new fine-tuning
Kconfig SPL_USE_TINY_PRINTF_POINTER_SUPPORT for pointer formatting
has been added. If it is enabled, the output of %pa / %pap should
be correct, and if it is disabled, the pointer formatting is
completely unsupported. In addition to indicate unsupported formatting,
'?' will be output. This allows enabling pointer formatting only
when needed. For SPL_NET and NET_LWIP it is selected by default.
Then it also supports the formatting with %pm, %pM and %pI4.

In summery this level of %p support for tiny printf is possible now:

1) The standard tiny printf won't have support for pointer formatting.
   So it doesn't print misleading values for %pa, instead '?' will be
   output:
   %p   => ?
   %pa  => ?a
   %pap => ?ap

2) If SPL_USE_TINY_PRINTF_POINTER_SUPPORT is enabled or DEBUG is defined
   tiny printf supports formatting %p and %pa / %pap.

3) If SPL_NET or NET_LWIP is enabled the support of pointers is extended
   for %pm, %pM and %pI4.

Signed-off-by: Christoph Niedermaier <cniedermaier at dh-electronics.com>
---
Cc: Tom Rini <trini at konsulko.com>
Cc: Simon Glass <sjg at chromium.org>
Cc: Michael Walle <mwalle at kernel.org>
Cc: Quentin Schulz <quentin.schulz at cherry.de>
Cc: Marek Vasut <marex at denx.de>
Cc: Benedikt Spranger <b.spranger at linutronix.de>
Cc: Jerome Forissier <jerome.forissier at linaro.org>
Cc: John Ogness <john.ogness at linutronix.de>
Cc: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
V2: - Rebase on current master
    - Extend commit message
    - Restrict use to SPL
    - Rename Kconfig to SPL_USE_TINY_PRINTF_POINTER_SUPPORT
    - Replace _DEBUG with defined(DEBUG)
    - Output '?' if %pm, %pM and %pI4 isn't available
    - Add break on case '%'
V3: - Add missing output '?' for the default case
---
 Kconfig            |  1 +
 common/spl/Kconfig |  1 +
 lib/Kconfig        |  8 +++++++
 lib/tiny-printf.c  | 52 +++++++++++++++++++++++-----------------------
 4 files changed, 36 insertions(+), 26 deletions(-)

diff --git a/Kconfig b/Kconfig
index 51358633762..b8eec3fc931 100644
--- a/Kconfig
+++ b/Kconfig
@@ -774,6 +774,7 @@ config NET
 
 config NET_LWIP
 	bool "Use lwIP for networking stack"
+	select SPL_USE_TINY_PRINTF_POINTER_SUPPORT if SPL_USE_TINY_PRINTF
 	imply NETDEVICES
 	help
 	  Include networking support based on the lwIP (lightweight IP)
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index b076f49ac00..b89e0c9b4d4 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1116,6 +1116,7 @@ config SPL_DM_SPI_FLASH
 config SPL_NET
 	bool "Support networking"
 	depends on !NET_LWIP
+	select SPL_USE_TINY_PRINTF_POINTER_SUPPORT if SPL_USE_TINY_PRINTF
 	help
 	  Enable support for network devices (such as Ethernet) in SPL.
 	  This permits SPL to load U-Boot over a network link rather than
diff --git a/lib/Kconfig b/lib/Kconfig
index b2aecd8a49e..e17396701c2 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -253,6 +253,14 @@ config VPL_USE_TINY_PRINTF
 
 	  The supported format specifiers are %c, %s, %u/%d and %x.
 
+config SPL_USE_TINY_PRINTF_POINTER_SUPPORT
+	bool "Extend tiny printf with the pointer formatting %p"
+	depends on SPL_USE_TINY_PRINTF
+	help
+	  This option enables the formatting of pointers %p. It supports
+	  %p and %pa / %pap. If this option is selected by SPL_NET or NET_LWIP
+	  it also supports the formatting with %pm, %pM and %pI4.
+
 config PANIC_HANG
 	bool "Do not reset the system on fatal error"
 	help
diff --git a/lib/tiny-printf.c b/lib/tiny-printf.c
index 2a7a4d286c0..6bbf8fb42a5 100644
--- a/lib/tiny-printf.c
+++ b/lib/tiny-printf.c
@@ -47,7 +47,7 @@ static void div_out(struct printf_info *info, unsigned long *num,
 		out_dgt(info, dgt);
 }
 
-#ifdef CONFIG_SPL_NET
+#if defined(CONFIG_SPL_NET) || defined(CONFIG_NET_LWIP)
 static void string(struct printf_info *info, char *s)
 {
 	char ch;
@@ -141,7 +141,7 @@ static void ip4_addr_string(struct printf_info *info, u8 *addr)
 
 	string(info, ip4_addr);
 }
-#endif
+#endif /* defined(CONFIG_SPL_NET) || defined(CONFIG_NET_LWIP) */
 
 /*
  * Show a '%p' thing.  A kernel extension is that the '%p' is followed
@@ -157,18 +157,14 @@ static void ip4_addr_string(struct printf_info *info, u8 *addr)
  *       decimal).
  */
 
-static void __maybe_unused pointer(struct printf_info *info, const char *fmt,
-				   void *ptr)
+#if defined(CONFIG_SPL_USE_TINY_PRINTF_POINTER_SUPPORT) || defined(DEBUG)
+static void pointer(struct printf_info *info, const char *fmt, void *ptr)
 {
-#ifdef DEBUG
 	unsigned long num = (uintptr_t)ptr;
 	unsigned long div;
-#endif
 
 	switch (*fmt) {
-#ifdef DEBUG
 	case 'a':
-
 		switch (fmt[1]) {
 		case 'p':
 		default:
@@ -176,8 +172,7 @@ static void __maybe_unused pointer(struct printf_info *info, const char *fmt,
 			break;
 		}
 		break;
-#endif
-#ifdef CONFIG_SPL_NET
+#if defined(CONFIG_SPL_NET) || defined(CONFIG_NET_LWIP)
 	case 'm':
 		return mac_address_string(info, ptr, false);
 	case 'M':
@@ -185,16 +180,22 @@ static void __maybe_unused pointer(struct printf_info *info, const char *fmt,
 	case 'I':
 		if (fmt[1] == '4')
 			return ip4_addr_string(info, ptr);
+#else
+	case 'm':
+	case 'M':
+	case 'I':
+		out(info, '?');
+		return;
 #endif
 	default:
 		break;
 	}
-#ifdef DEBUG
+
 	div = 1UL << (sizeof(long) * 8 - 4);
 	for (; div; div /= 0x10)
 		div_out(info, &num, div);
-#endif
 }
+#endif
 
 static int _vprintf(struct printf_info *info, const char *fmt, va_list va)
 {
@@ -269,21 +270,18 @@ static int _vprintf(struct printf_info *info, const char *fmt, va_list va)
 						div_out(info, &num, div);
 				}
 				break;
+#if defined(CONFIG_SPL_USE_TINY_PRINTF_POINTER_SUPPORT) || defined(DEBUG)
 			case 'p':
-				if (CONFIG_IS_ENABLED(NET) ||
-				    CONFIG_IS_ENABLED(NET_LWIP) || _DEBUG) {
-					pointer(info, fmt, va_arg(va, void *));
-					/*
-					 * Skip this because it pulls in _ctype which is
-					 * 256 bytes, and we don't generally implement
-					 * pointer anyway
-					 */
-					while (isalnum(fmt[0]))
-						fmt++;
-					break;
-				}
-				islong = true;
-				fallthrough;
+				pointer(info, fmt, va_arg(va, void *));
+				/*
+				 * Skip this because it pulls in _ctype which is
+				 * 256 bytes, and we don't generally implement
+				 * pointer anyway
+				 */
+				while (isalnum(fmt[0]))
+					fmt++;
+				break;
+#endif
 			case 'x':
 			case 'X':
 				if (islong) {
@@ -310,7 +308,9 @@ static int _vprintf(struct printf_info *info, const char *fmt, va_list va)
 				break;
 			case '%':
 				out(info, '%');
+				break;
 			default:
+				out(info, '?');
 				break;
 			}
 
-- 
2.30.2

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