[PATCH] net/mlx5: fpga: avoid uninitialized return codes

calling mlx5_fpga_mem_{read,write}_i2c() with a zero length on
older compiler version such as gcc-4.6 results in a warning that
the return code is not initialized:

drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:147:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]
drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:126:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]

On newer compilers, the 'err' variable is optimized away in this
code path and assumed to be zero when the loop completes, so we
don't get this warning.

I'm changing the function here to instead return -EINVAL for the
case, under the assumption that it was never meant to be called
with a zero length argument.

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82203
Signed-off-by: Arnd Bergmann <redacted>
---
 drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c b/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c
index 3c11d6e2160a..914fb9d77a1a 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c

@@ -64,7 +64,7 @@ static int mlx5_fpga_mem_read_i2c(struct mlx5_fpga_device *fdev, size_t size,
 	size_t max_size = MLX5_FPGA_ACCESS_REG_SIZE_MAX;
 	size_t bytes_done = 0;
 	u8 actual_size;
-	int err;
+	int err = -EINVAL;
 
 	if (!fdev->mdev)
 		return -ENOTCONN;

@@ -93,7 +93,7 @@ static int mlx5_fpga_mem_write_i2c(struct mlx5_fpga_device *fdev, size_t size,
 	size_t max_size = MLX5_FPGA_ACCESS_REG_SIZE_MAX;
 	size_t bytes_done = 0;
 	u8 actual_size;
-	int err;
+	int err = -EINVAL;
 
 	if (!fdev->mdev)
 		return -ENOTCONN;

-- 
2.9.0

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On Thu, Sep 14, 2017 at 01:06:18PM +0200, Arnd Bergmann wrote:

calling mlx5_fpga_mem_{read,write}_i2c() with a zero length on
older compiler version such as gcc-4.6 results in a warning that
the return code is not initialized:

drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:147:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]
drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:126:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]

On newer compilers, the 'err' variable is optimized away in this
code path and assumed to be zero when the loop completes, so we
don't get this warning.

I'm changing the function here to instead return -EINVAL for the
case, under the assumption that it was never meant to be called
with a zero length argument.

I agree with you that size can't be zero and this patch will fix the
warning, but if it is possible, I will prefer to have this check is
written explicitly and not implicitly.

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c b/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c
index 3c11d6e2160a..0e85bebe1dad 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c

@@ -69,6 +69,9 @@ static int mlx5_fpga_mem_read_i2c(struct mlx5_fpga_device *fdev, size_t size,
 	if (!fdev->mdev)
 		return -ENOTCONN;

+	if (!size)
+		return -EINVAL;
+
 	while (bytes_done < size) {
 		actual_size = min(max_size, (size - bytes_done));

Thanks

On Thu, Sep 14, 2017 at 5:54 AM, Leon Romanovsky [off-list ref] wrote:

On Thu, Sep 14, 2017 at 01:06:18PM +0200, Arnd Bergmann wrote:

quoted

calling mlx5_fpga_mem_{read,write}_i2c() with a zero length on
older compiler version such as gcc-4.6 results in a warning that
the return code is not initialized:

drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:147:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]
drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c:126:6: error: ‘err’ may be used uninitialized in this function [-Werror=uninitialized]

On newer compilers, the 'err' variable is optimized away in this
code path and assumed to be zero when the loop completes, so we
don't get this warning.

I'm changing the function here to instead return -EINVAL for the
case, under the assumption that it was never meant to be called
with a zero length argument.

Thanks Arnd, Looks good.

Or simply trust the caller :), and avoid redundant code.

        while (bytes_done < size) {
                actual_size = min(max_size, (size - bytes_done));

Thanks

quoted

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82203
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c b/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c
index 3c11d6e2160a..914fb9d77a1a 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fpga/sdk.c

@@ -64,7 +64,7 @@ static int mlx5_fpga_mem_read_i2c(struct mlx5_fpga_device *fdev, size_t size,
      size_t max_size = MLX5_FPGA_ACCESS_REG_SIZE_MAX;
      size_t bytes_done = 0;
      u8 actual_size;
-     int err;
+     int err = -EINVAL;

      if (!fdev->mdev)
              return -ENOTCONN;

@@ -93,7 +93,7 @@ static int mlx5_fpga_mem_write_i2c(struct mlx5_fpga_device *fdev, size_t size,
      size_t max_size = MLX5_FPGA_ACCESS_REG_SIZE_MAX;
      size_t bytes_done = 0;
      u8 actual_size;
-     int err;
+     int err = -EINVAL;

      if (!fdev->mdev)
              return -ENOTCONN;
--

2.9.0

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