Subject: [PATCH] [v2] net: sfc: avoid format string warning

From: Arnd Bergmann <[email-masked]>
Date: Wed, 25 Mar 2026 14:45:44 +0100

From: Arnd Bergmann <[email-masked]>

Three sfc drivers contain the same *_fill_test() function that takes
a format string argument that gets passed down to snprintf(), producing
a warning with clang-22:

drivers/net/ethernet/sfc/falcon/ethtool.c:227:60: error: diagnostic behavior may be improved by adding
      the 'format(printf, 7, 8)' attribute to the declaration of 'ef4_fill_test' [-Werror,-Wmissing-format-attribute]
  210 |                 snprintf(test_str, sizeof(test_str), test_format, test_id);
      |                                                                          ^
drivers/net/ethernet/sfc/falcon/ethtool.c:210:13: note: 'ef4_fill_test' declared here

Rework these to take a varargs based test_format that allows better
type checking and a non-varargs unit name that gets pre-filled by
the caller, so that the compiler can validate all format strings.

Fixes: 3273c2e8c66a ("[netdrvr] sfc: sfc: Add self-test support")
Signed-off-by: Arnd Bergmann <[email-masked]>
---
v2: open-code the unit name format as well
    reformat the function prototype
---
 drivers/net/ethernet/sfc/ethtool_common.c     | 67 +++++++++---------
 drivers/net/ethernet/sfc/falcon/ethtool.c     | 68 +++++++++---------
 .../net/ethernet/sfc/siena/ethtool_common.c   | 69 +++++++++----------
 3 files changed, 99 insertions(+), 105 deletions(-)

diff --git a/drivers/net/ethernet/sfc/ethtool_common.c b/drivers/net/ethernet/sfc/ethtool_common.c
index 54f8e4626568..62a94c995241 100644
--- a/drivers/net/ethernet/sfc/ethtool_common.c
+++ b/drivers/net/ethernet/sfc/ethtool_common.c
@@ -247,18 +247,17 @@ int efx_ethtool_set_pauseparam(struct net_device *net_dev,
  * @strings:		Ethtool strings, or %NULL
  * @data:		Ethtool test results, or %NULL
  * @test:		Pointer to test result (used only if data != %NULL)
- * @unit_format:	Unit name format (e.g. "chan\%d")
- * @unit_id:		Unit id (e.g. 0 for "chan0")
+ * @unit_name:		Unit name
  * @test_format:	Test name format (e.g. "loopback.\%s.tx.sent")
- * @test_id:		Test id (e.g. "PHYXS" for "loopback.PHYXS.tx_sent")
  *
  * Fill in an individual self-test entry.
  */
-static void efx_fill_test(unsigned int test_index, u8 *strings, u64 *data,
-			  int *test, const char *unit_format, int unit_id,
-			  const char *test_format, const char *test_id)
+static void __printf(6, 7) efx_fill_test(unsigned int test_index, u8 *strings,
+					 u64 *data, int *test,
+					 const char *unit_name,
+					 const char *test_format, ...)
 {
-	char unit_str[ETH_GSTRING_LEN], test_str[ETH_GSTRING_LEN];
+	char test_str[ETH_GSTRING_LEN];
 
 	/* Fill data value, if applicable */
 	if (data)
@@ -266,20 +265,16 @@ static void efx_fill_test(unsigned int test_index, u8 *strings, u64 *data,
 
 	/* Fill string, if applicable */
 	if (strings) {
-		if (strchr(unit_format, '%'))
-			snprintf(unit_str, sizeof(unit_str),
-				 unit_format, unit_id);
-		else
-			strcpy(unit_str, unit_format);
-		snprintf(test_str, sizeof(test_str), test_format, test_id);
+		va_list args;
+
+		va_start(args, test_format);
+		vsnprintf(test_str, sizeof(test_str), test_format, args);
+		va_end(args);
 		snprintf(strings + test_index * ETH_GSTRING_LEN,
-			 ETH_GSTRING_LEN,
-			 "%-6s %-24s", unit_str, test_str);
+			 ETH_GSTRING_LEN, "%-6s %-24s", unit_name, test_str);
 	}
 }
 
-#define EFX_CHANNEL_NAME(_channel) "chan%d", _channel->channel
-#define EFX_TX_QUEUE_NAME(_tx_queue) "txq%d", _tx_queue->label
 #define EFX_LOOPBACK_NAME(_mode, _counter)			\
 	"loopback.%s." _counter, STRING_TABLE_LOOKUP(_mode, efx_loopback_mode)
 
@@ -306,23 +301,23 @@ static int efx_fill_loopback_test(struct efx_nic *efx,
 	struct efx_tx_queue *tx_queue;
 
 	efx_for_each_channel_tx_queue(tx_queue, channel) {
+		char unit_str[ETH_GSTRING_LEN];
+
+		snprintf(unit_str, sizeof(unit_str), "txq%d", tx_queue->label);
+
 		efx_fill_test(test_index++, strings, data,
 			      &lb_tests->tx_sent[tx_queue->label],
-			      EFX_TX_QUEUE_NAME(tx_queue),
-			      EFX_LOOPBACK_NAME(mode, "tx_sent"));
+			      unit_str, EFX_LOOPBACK_NAME(mode, "tx_sent"));
 		efx_fill_test(test_index++, strings, data,
 			      &lb_tests->tx_done[tx_queue->label],
-			      EFX_TX_QUEUE_NAME(tx_queue),
-			      EFX_LOOPBACK_NAME(mode, "tx_done"));
+			      unit_str, EFX_LOOPBACK_NAME(mode, "tx_done"));
 	}
 	efx_fill_test(test_index++, strings, data,
 		      &lb_tests->rx_good,
-		      "rx", 0,
-		      EFX_LOOPBACK_NAME(mode, "rx_good"));
+		      "rx", EFX_LOOPBACK_NAME(mode, "rx_good"));
 	efx_fill_test(test_index++, strings, data,
 		      &lb_tests->rx_bad,
-		      "rx", 0,
-		      EFX_LOOPBACK_NAME(mode, "rx_bad"));
+		      "rx", EFX_LOOPBACK_NAME(mode, "rx_bad"));
 
 	return test_index;
 }
@@ -349,28 +344,30 @@ int efx_ethtool_fill_self_tests(struct efx_nic *efx,
 	enum efx_loopback_mode mode;
 
 	efx_fill_test(n++, strings, data, &tests->phy_alive,
-		      "phy", 0, "alive", NULL);
+		      "phy", "alive");
 	efx_fill_test(n++, strings, data, &tests->nvram,
-		      "core", 0, "nvram", NULL);
+		      "core", "nvram");
 	efx_fill_test(n++, strings, data, &tests->interrupt,
-		      "core", 0, "interrupt", NULL);
+		      "core", "interrupt");
 
 	/* Event queues */
 	efx_for_each_channel(channel, efx) {
+		char unit_str[ETH_GSTRING_LEN];
+
+		snprintf(unit_str, sizeof(unit_str), "txq%d", channel->channel);
+
 		efx_fill_test(n++, strings, data,
 			      &tests->eventq_dma[channel->channel],
-			      EFX_CHANNEL_NAME(channel),
-			      "eventq.dma", NULL);
+			      unit_str, "eventq.dma");
 		efx_fill_test(n++, strings, data,
 			      &tests->eventq_int[channel->channel],
-			      EFX_CHANNEL_NAME(channel),
-			      "eventq.int", NULL);
+			      unit_str, "eventq.int");
 	}
 
 	efx_fill_test(n++, strings, data, &tests->memory,
-		      "core", 0, "memory", NULL);
+		      "core", "memory");
 	efx_fill_test(n++, strings, data, &tests->registers,
-		      "core", 0, "registers", NULL);
+		      "core", "registers");
 
 	for (i = 0; true; ++i) {
 		const char *name;
@@ -380,7 +377,7 @@ int efx_ethtool_fill_self_tests(struct efx_nic *efx,
 		if (name == NULL)
 			break;
 
-		efx_fill_test(n++, strings, data, &tests->phy_ext[i], "phy", 0, name, NULL);
+		efx_fill_test(n++, strings, data, &tests->phy_ext[i], "phy", "%s", name);
 	}
 
 	/* Loopback tests */
diff --git a/drivers/net/ethernet/sfc/falcon/ethtool.c b/drivers/net/ethernet/sfc/falcon/ethtool.c
index 807c587eba3b..260340b291d3 100644
--- a/drivers/net/ethernet/sfc/falcon/ethtool.c
+++ b/drivers/net/ethernet/sfc/falcon/ethtool.c
@@ -200,18 +200,17 @@ static void ef4_ethtool_set_msglevel(struct net_device *net_dev, u32 msg_enable)
  * @strings:		Ethtool strings, or %NULL
  * @data:		Ethtool test results, or %NULL
  * @test:		Pointer to test result (used only if data != %NULL)
- * @unit_format:	Unit name format (e.g. "chan\%d")
- * @unit_id:		Unit id (e.g. 0 for "chan0")
+ * @unit_name:		Unit name
  * @test_format:	Test name format (e.g. "loopback.\%s.tx.sent")
- * @test_id:		Test id (e.g. "PHYXS" for "loopback.PHYXS.tx_sent")
  *
  * Fill in an individual self-test entry.
  */
-static void ef4_fill_test(unsigned int test_index, u8 *strings, u64 *data,
-			  int *test, const char *unit_format, int unit_id,
-			  const char *test_format, const char *test_id)
+static void __printf(6, 7) ef4_fill_test(unsigned int test_index, u8 *strings,
+					 u64 *data, int *test,
+					 const char *unit_name,
+					 const char *test_format, ...)
 {
-	char unit_str[ETH_GSTRING_LEN], test_str[ETH_GSTRING_LEN];
+	char test_str[ETH_GSTRING_LEN];
 
 	/* Fill data value, if applicable */
 	if (data)
@@ -219,21 +218,17 @@ static void ef4_fill_test(unsigned int test_index, u8 *strings, u64 *data,
 
 	/* Fill string, if applicable */
 	if (strings) {
-		if (strchr(unit_format, '%'))
-			snprintf(unit_str, sizeof(unit_str),
-				 unit_format, unit_id);
-		else
-			strcpy(unit_str, unit_format);
-		snprintf(test_str, sizeof(test_str), test_format, test_id);
+		va_list arg;
+
+		va_start(arg, test_format);
+		vsnprintf(test_str, sizeof(test_str), test_format, arg);
+		va_end(arg);
 		snprintf(strings + test_index * ETH_GSTRING_LEN,
 			 ETH_GSTRING_LEN,
-			 "%-6s %-24s", unit_str, test_str);
+			 "%-6s %-24s", unit_name, test_str);
 	}
 }
 
-#define EF4_CHANNEL_NAME(_channel) "chan%d", _channel->channel
-#define EF4_TX_QUEUE_NAME(_tx_queue) "txq%d", _tx_queue->queue
-#define EF4_RX_QUEUE_NAME(_rx_queue) "rxq%d", _rx_queue->queue
 #define EF4_LOOPBACK_NAME(_mode, _counter)			\
 	"loopback.%s." _counter, STRING_TABLE_LOOKUP(_mode, ef4_loopback_mode)
 
@@ -260,23 +255,23 @@ static int ef4_fill_loopback_test(struct ef4_nic *efx,
 	struct ef4_tx_queue *tx_queue;
 
 	ef4_for_each_channel_tx_queue(tx_queue, channel) {
+		char unit_str[ETH_GSTRING_LEN];
+
+		snprintf(unit_str, sizeof(unit_str), "txq%d", tx_queue->queue);
+
 		ef4_fill_test(test_index++, strings, data,
 			      &lb_tests->tx_sent[tx_queue->queue],
-			      EF4_TX_QUEUE_NAME(tx_queue),
-			      EF4_LOOPBACK_NAME(mode, "tx_sent"));
+			      unit_str, EF4_LOOPBACK_NAME(mode, "tx_sent"));
 		ef4_fill_test(test_index++, strings, data,
 			      &lb_tests->tx_done[tx_queue->queue],
-			      EF4_TX_QUEUE_NAME(tx_queue),
-			      EF4_LOOPBACK_NAME(mode, "tx_done"));
+			      unit_str, EF4_LOOPBACK_NAME(mode, "tx_done"));
 	}
 	ef4_fill_test(test_index++, strings, data,
 		      &lb_tests->rx_good,
-		      "rx", 0,
-		      EF4_LOOPBACK_NAME(mode, "rx_good"));
+		      "rx", EF4_LOOPBACK_NAME(mode, "rx_good"));
 	ef4_fill_test(test_index++, strings, data,
 		      &lb_tests->rx_bad,
-		      "rx", 0,
-		      EF4_LOOPBACK_NAME(mode, "rx_bad"));
+		      "rx", EF4_LOOPBACK_NAME(mode, "rx_bad"));
 
 	return test_index;
 }
@@ -303,28 +298,31 @@ static int ef4_ethtool_fill_self_tests(struct ef4_nic *efx,
 	enum ef4_loopback_mode mode;
 
 	ef4_fill_test(n++, strings, data, &tests->phy_alive,
-		      "phy", 0, "alive", NULL);
+		      "phy", "alive");
 	ef4_fill_test(n++, strings, data, &tests->nvram,
-		      "core", 0, "nvram", NULL);
+		      "core", "nvram");
 	ef4_fill_test(n++, strings, data, &tests->interrupt,
-		      "core", 0, "interrupt", NULL);
+		      "core", "interrupt");
 
 	/* Event queues */
 	ef4_for_each_channel(channel, efx) {
+		char unit_str[ETH_GSTRING_LEN];
+
+		snprintf(unit_str, sizeof(unit_str), "chan%d",
+			 channel->channel);
+
 		ef4_fill_test(n++, strings, data,
 			      &tests->eventq_dma[channel->channel],
-			      EF4_CHANNEL_NAME(channel),
-			      "eventq.dma", NULL);
+			      unit_str, "eventq.dma");
 		ef4_fill_test(n++, strings, data,
 			      &tests->eventq_int[channel->channel],
-			      EF4_CHANNEL_NAME(channel),
-			      "eventq.int", NULL);
+			      unit_str, "eventq.int");
 	}
 
 	ef4_fill_test(n++, strings, data, &tests->memory,
-		      "core", 0, "memory", NULL);
+		      "core", "memory");
 	ef4_fill_test(n++, strings, data, &tests->registers,
-		      "core", 0, "registers", NULL);
+		      "core", "registers");
 
 	if (efx->phy_op->run_tests != NULL) {
 		EF4_BUG_ON_PARANOID(efx->phy_op->test_name == NULL);
@@ -338,7 +336,7 @@ static int ef4_ethtool_fill_self_tests(struct ef4_nic *efx,
 				break;
 
 			ef4_fill_test(n++, strings, data, &tests->phy_ext[i],
-				      "phy", 0, name, NULL);
+				      "phy", "%s", name);
 		}
 	}
 
diff --git a/drivers/net/ethernet/sfc/siena/ethtool_common.c b/drivers/net/ethernet/sfc/siena/ethtool_common.c
index 76cbce2b9592..e49cc604b43a 100644
--- a/drivers/net/ethernet/sfc/siena/ethtool_common.c
+++ b/drivers/net/ethernet/sfc/siena/ethtool_common.c
@@ -199,18 +199,17 @@ int efx_siena_ethtool_set_pauseparam(struct net_device *net_dev,
  * @strings:		Ethtool strings, or %NULL
  * @data:		Ethtool test results, or %NULL
  * @test:		Pointer to test result (used only if data != %NULL)
- * @unit_format:	Unit name format (e.g. "chan\%d")
- * @unit_id:		Unit id (e.g. 0 for "chan0")
+ * @unit_name:		Unit name
  * @test_format:	Test name format (e.g. "loopback.\%s.tx.sent")
- * @test_id:		Test id (e.g. "PHYXS" for "loopback.PHYXS.tx_sent")
  *
  * Fill in an individual self-test entry.
  */
-static void efx_fill_test(unsigned int test_index, u8 *strings, u64 *data,
-			  int *test, const char *unit_format, int unit_id,
-			  const char *test_format, const char *test_id)
+static void __printf(6, 7) efx_fill_test(unsigned int test_index, u8 *strings,
+					 u64 *data, int *test,
+					 const char *unit_name,
+					 char *test_format, ...)
 {
-	char unit_str[ETH_GSTRING_LEN], test_str[ETH_GSTRING_LEN];
+	char test_str[ETH_GSTRING_LEN];
 
 	/* Fill data value, if applicable */
 	if (data)
@@ -218,20 +217,16 @@ static void efx_fill_test(unsigned int test_index, u8 *strings, u64 *data,
 
 	/* Fill string, if applicable */
 	if (strings) {
-		if (strchr(unit_format, '%'))
-			snprintf(unit_str, sizeof(unit_str),
-				 unit_format, unit_id);
-		else
-			strcpy(unit_str, unit_format);
-		snprintf(test_str, sizeof(test_str), test_format, test_id);
+		va_list args;
+
+		va_start(args, test_format);
+		vsnprintf(test_str, sizeof(test_str), test_format, args);
+		va_end(args);
 		snprintf(strings + test_index * ETH_GSTRING_LEN,
-			 ETH_GSTRING_LEN,
-			 "%-6s %-24s", unit_str, test_str);
+			 ETH_GSTRING_LEN, "%-6s %-24s", unit_name, test_str);
 	}
 }
 
-#define EFX_CHANNEL_NAME(_channel) "chan%d", _channel->channel
-#define EFX_TX_QUEUE_NAME(_tx_queue) "txq%d", _tx_queue->label
 #define EFX_LOOPBACK_NAME(_mode, _counter)			\
 	"loopback.%s." _counter, STRING_TABLE_LOOKUP(_mode, efx_siena_loopback_mode)
 
@@ -258,23 +253,23 @@ static int efx_fill_loopback_test(struct efx_nic *efx,
 	struct efx_tx_queue *tx_queue;
 
 	efx_for_each_channel_tx_queue(tx_queue, channel) {
+		char unit_str[ETH_GSTRING_LEN];
+
+		snprintf(unit_str, sizeof(unit_str), "txq%d",tx_queue->label);
+
 		efx_fill_test(test_index++, strings, data,
 			      &lb_tests->tx_sent[tx_queue->label],
-			      EFX_TX_QUEUE_NAME(tx_queue),
-			      EFX_LOOPBACK_NAME(mode, "tx_sent"));
+			      unit_str, EFX_LOOPBACK_NAME(mode, "tx_sent"));
 		efx_fill_test(test_index++, strings, data,
 			      &lb_tests->tx_done[tx_queue->label],
-			      EFX_TX_QUEUE_NAME(tx_queue),
-			      EFX_LOOPBACK_NAME(mode, "tx_done"));
+			      unit_str, EFX_LOOPBACK_NAME(mode, "tx_done"));
 	}
 	efx_fill_test(test_index++, strings, data,
 		      &lb_tests->rx_good,
-		      "rx", 0,
-		      EFX_LOOPBACK_NAME(mode, "rx_good"));
+		      "rx", EFX_LOOPBACK_NAME(mode, "rx_good"));
 	efx_fill_test(test_index++, strings, data,
 		      &lb_tests->rx_bad,
-		      "rx", 0,
-		      EFX_LOOPBACK_NAME(mode, "rx_bad"));
+		      "rx", EFX_LOOPBACK_NAME(mode, "rx_bad"));
 
 	return test_index;
 }
@@ -301,28 +296,31 @@ static int efx_ethtool_fill_self_tests(struct efx_nic *efx,
 	enum efx_loopback_mode mode;
 
 	efx_fill_test(n++, strings, data, &tests->phy_alive,
-		      "phy", 0, "alive", NULL);
+		      "phy", "alive");
 	efx_fill_test(n++, strings, data, &tests->nvram,
-		      "core", 0, "nvram", NULL);
+		      "core", "nvram");
 	efx_fill_test(n++, strings, data, &tests->interrupt,
-		      "core", 0, "interrupt", NULL);
+		      "core", "interrupt");
 
 	/* Event queues */
 	efx_for_each_channel(channel, efx) {
+		char unit_str[ETH_GSTRING_LEN];
+
+		snprintf(unit_str, sizeof(unit_str), "chan%d",
+			 channel->channel);
+
 		efx_fill_test(n++, strings, data,
 			      &tests->eventq_dma[channel->channel],
-			      EFX_CHANNEL_NAME(channel),
-			      "eventq.dma", NULL);
+			      unit_str, "eventq.dma");
 		efx_fill_test(n++, strings, data,
 			      &tests->eventq_int[channel->channel],
-			      EFX_CHANNEL_NAME(channel),
-			      "eventq.int", NULL);
+			      unit_str, "eventq.int");
 	}
 
 	efx_fill_test(n++, strings, data, &tests->memory,
-		      "core", 0, "memory", NULL);
+		      "core", "memory");
 	efx_fill_test(n++, strings, data, &tests->registers,
-		      "core", 0, "registers", NULL);
+		      "core", "registers");
 
 	for (i = 0; true; ++i) {
 		const char *name;
@@ -332,7 +330,8 @@ static int efx_ethtool_fill_self_tests(struct efx_nic *efx,
 		if (name == NULL)
 			break;
 
-		efx_fill_test(n++, strings, data, &tests->phy_ext[i], "phy", 0, name, NULL);
+		efx_fill_test(n++, strings, data, &tests->phy_ext[i], "phy",
+			      "%s", name);
 	}
 
 	/* Loopback tests */
-- 
2.39.5