mlxsw: Fix -Wformat-truncation warnings

Ido Schimmel writes:

Commit 6d4ab2e97dcf ("extrawarn: enable format and stringop overflow warnings in W=1") enabled format warnings as part of W=1 builds, resulting in two new warnings in mlxsw. Fix both and target at net-next as the warnings are not indicative of actual bugs.

Ido Schimmel (2):
mlxsw: core_thermal: Fix -Wformat-truncation warning
mlxsw: spectrum_ethtool: Fix -Wformat-truncation warning

 drivers/net/ethernet/mellanox/mlxsw/core_thermal.c     | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

2.41.0

From: Ido Schimmel <[email protected]>

The name of a thermal zone device cannot be longer than 19 characters ('THERMAL_NAME_LENGTH - 1'). The format string 'mlxsw-lc%d-gearbox%d' can exceed this limitation if the maximum number of line cards and the maximum number of gearboxes on each line card cannot be represented using a single digit.

This is not the case with current systems nor future ones. Therefore, increase the size of the result buffer beyond 'THERMAL_NAME_LENGTH' and suppress the following build warning [1].

If this limitation is ever exceeded, we will know about it since the thermal core validates the thermal device's name during registration.

[1]
drivers/net/ethernet/mellanox/mlxsw/core_thermal.c: In function ‘mlxsw_thermal_gearboxes_init.constprop’:
drivers/net/ethernet/mellanox/mlxsw/core_thermal.c:543:71: error: ‘%d’ directive output may be truncated writing between 1 and 3 bytes into a region of size between 1 and 3 [-Werror=format-truncation=]
543 | snprintf(tz_name, sizeof(tz_name), "mlxsw-lc%d-gearbox%d",
| ^~
In function ‘mlxsw_thermal_gearbox_tz_init’,
inlined from ‘mlxsw_thermal_gearboxes_init.constprop’ at drivers/net/ethernet/mellanox/mlxsw/core_thermal.c:611:9:
drivers/net/ethernet/mellanox/mlxsw/core_thermal.c:543:52: note: directive argument in the range [1, 255]
543 | snprintf(tz_name, sizeof(tz_name), "mlxsw-lc%d-gearbox%d",

      |                                                    ^~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/mellanox/mlxsw/core_thermal.c:543:17: note: ‘snprintf’ output between 19 and 23 bytes into a destination of size 20
  543 |                 snprintf(tz_name, sizeof(tz_name), "mlxsw-lc%d-gearbox%d",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  544 |                          gearbox_tz->slot_index, gearbox_tz->module + 1);
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

---
 drivers/net/ethernet/mellanox/mlxsw/core_thermal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index f709e44c76a8..f1b48d6615f6 100644
@@ -536,7 +536,7 @@ mlxsw_thermal_modules_fini(struct mlxsw_thermal *thermal,
 static int
 mlxsw_thermal_gearbox_tz_init(struct mlxsw_thermal_module *gearbox_tz)
 {
-	char tz_name[THERMAL_NAME_LENGTH];
+	char tz_name[40];
 	int ret;
 
 	if (gearbox_tz->slot_index)

2.41.0

From: Ido Schimmel <[email protected]>

Ethtool stats strings cannot be longer than 32 characters ('ETH_GSTRING_LEN'), including the terminating null byte. The format string '%.29s_%.1d' can exceed this limitation if the per-TC counter name exceeds 28 characters. Together with the underscore, the two digits of the TC (bounded at 16) and the terminating null byte, more than 32 characters will be used.

Fix this by bounding the counter name at 28 characters which suppresses the following build warning [1]. This does not affect ethtool output since the longest counter name does not exceed this limitation.

[1]
drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c: In function ‘mlxsw_sp_port_get_strings’:
drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c:622:58: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
622 | snprintf(*p, ETH_GSTRING_LEN, "%.29s_%.1d",
| ^
In function ‘mlxsw_sp_port_get_tc_strings’,
inlined from ‘mlxsw_sp_port_get_strings’ at drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c:677:4:
drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c:622:17: note: ‘snprintf’ output between 3 and 33 bytes into a destination of size 32

  622 |                 snprintf(*p, ETH_GSTRING_LEN, "%.29s_%.1d",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  623 |                          mlxsw_sp_port_hw_tc_stats[i].str, tc);
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c: In function ‘mlxsw_sp_port_get_strings’:
drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c:622:58: error: ‘snprintf’ output may be truncated before the last format character [-Werror=format-truncation=]
622 | snprintf(*p, ETH_GSTRING_LEN, "%.29s_%.1d",
| ^
In function ‘mlxsw_sp_port_get_tc_strings’,
inlined from ‘mlxsw_sp_port_get_strings’ at drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c:677:4:
drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c:622:17: note: ‘snprintf’ output between 3 and 33 bytes into a destination of size 32

  622 |                 snprintf(*p, ETH_GSTRING_LEN, "%.29s_%.1d",
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  623 |                          mlxsw_sp_port_hw_tc_stats[i].str, tc);
      |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

---
 drivers/net/ethernet/mellanox/mlxsw/spectrum_ethtool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 472830d07ac1..0f29e9c19411 100644
@@ -619,7 +619,7 @@ static void mlxsw_sp_port_get_tc_strings(u8 **p, int tc)
 	int i;
 
 	for (i = 0; i < MLXSW_SP_PORT_HW_TC_STATS_LEN; i++) {
-		snprintf(*p, ETH_GSTRING_LEN, "%.29s_%.1d",
+		snprintf(*p, ETH_GSTRING_LEN, "%.28s_%d",
 			 mlxsw_sp_port_hw_tc_stats[i].str, tc);
 		*p += ETH_GSTRING_LEN;
 	}

2.41.0

For series,