[dpdk-dev] [PATCH] net/mlx: fix variadic macro

[Ali Alnubani <alialnu@mellanox.com>]

This rewrites the MKSTR macro appending an empty string to its arguments
to resolve build failures similar to:

  drivers/net/mlx4/mlx4.c:461:14: fatal error: format string is not a
  string literal [-Wformat-nonliteral]
          MKSTR(path, "%s/device/uevent", device->ibdev_path);

  drivers/net/mlx4/mlx4_utils.h:82:30: note: expanded from macro 'MKSTR'
          char name[snprintf(NULL, 0, __VA_ARGS__) + 1]; \

  drivers/net/mlx5/mlx5_stats.c:144:15: fatal error: format string is not a
  string literal [-Wformat-nonliteral]
  	MKSTR(path, "%s/ports/%d/hw_counters/%s",

  drivers/net/mlx5/mlx5_utils.h:149:30: note: expanded from macro 'MKSTR'
  	char name[snprintf(NULL, 0, __VA_ARGS__) + 1]; \

The errors reproduce with clang version 9.0.0, and the release notes
don't mention what could have caused them.

Fixes: 7fae69eeff13 ("mlx4: new poll mode driver")
Fixes: 771fa900b73a ("mlx5: introduce new driver for Mellanox ConnectX-4 adapters")
Cc: adrien.mazarguil@6wind.com
Cc: stable@dpdk.org

Signed-off-by: Ali Alnubani <alialnu@mellanox.com>
Signed-off-by: Matan Azrad <matan@mellanox.com>
---
 drivers/net/mlx4/mlx4_utils.h | 5 +++--
 drivers/net/mlx5/mlx5_utils.h | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/mlx4/mlx4_utils.h b/drivers/net/mlx4/mlx4_utils.h
index 74b9d2ecd..5718b9c74 100644
--- a/drivers/net/mlx4/mlx4_utils.h
+++ b/drivers/net/mlx4/mlx4_utils.h
@@ -79,9 +79,10 @@ pmd_drv_log_basename(const char *s)
 
 /** Allocate a buffer on the stack and fill it with a printf format string. */
 #define MKSTR(name, ...) \
-	char name[snprintf(NULL, 0, __VA_ARGS__) + 1]; \
+	int mkstr_size_##name = snprintf(NULL, 0, "" __VA_ARGS__); \
+	char name[mkstr_size_##name + 1]; \
 	\
-	snprintf(name, sizeof(name), __VA_ARGS__)
+	snprintf(name, sizeof(name), "" __VA_ARGS__)
 
 /** Generate a string out of the provided arguments. */
 #define MLX4_STR(...) # __VA_ARGS__
diff --git a/drivers/net/mlx5/mlx5_utils.h b/drivers/net/mlx5/mlx5_utils.h
index b4ed8c6da..ebf79b80a 100644
--- a/drivers/net/mlx5/mlx5_utils.h
+++ b/drivers/net/mlx5/mlx5_utils.h
@@ -146,9 +146,10 @@ extern int mlx5_logtype;
 
 /* Allocate a buffer on the stack and fill it with a printf format string. */
 #define MKSTR(name, ...) \
-	char name[snprintf(NULL, 0, __VA_ARGS__) + 1]; \
+	int mkstr_size_##name = snprintf(NULL, 0, "" __VA_ARGS__); \
+	char name[mkstr_size_##name + 1]; \
 	\
-	snprintf(name, sizeof(name), __VA_ARGS__)
+	snprintf(name, sizeof(name), "" __VA_ARGS__)
 
 /**
  * Return logarithm of the nearest power of two above input value.
-- 
2.24.0