"error: BUILD_BUG_ON failed: __mlx5_st_sz_bits(pcmr_reg) % 32" in drivers/net/ethernet/mellanox/mlx5/core/port.c: In function ‘mlx5_query_ports_check’

[GustavoARSilva]

When replacing the one-element array reserved_at_5f[1] with a flexible-array member in struct mlx5_ifc_pcmr_reg_bits:

diff --git a/include/linux/mlx5/mlx5_ifc.h b/include/linux/mlx5/mlx5_ifc.h
index 6b22e5a96f10..cbeef8a7b690 100644
--- a/include/linux/mlx5/mlx5_ifc.h
+++ b/include/linux/mlx5/mlx5_ifc.h
@@ -9219,7 +9219,7 @@ struct mlx5_ifc_pcmr_reg_bits {
        u8         entropy_gre_calc[0x1];
        u8         reserved_at_43[0x1b];
        u8         fcs_chk[0x1];
-       u8         reserved_at_5f[0x1];
+       u8         reserved_at_5f[];
 };

 struct mlx5_ifc_lane_2_module_mapping_bits {

the following error shows up:

                 from drivers/net/ethernet/mellanox/mlx5/core/port.c:33:
drivers/net/ethernet/mellanox/mlx5/core/port.c: In function ‘mlx5_query_ports_check’:
./include/linux/compiler.h:394:38: error: call to ‘__compiletime_assert_775’ declared with attribute error: BUILD_BUG_ON failed: __mlx5_st_sz_bits(pcmr_reg) % 32
  394 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                      ^
./include/linux/compiler.h:375:4: note: in definition of macro ‘__compiletime_assert’
  375 |    prefix ## suffix();    \
      |    ^~~~~~
./include/linux/compiler.h:394:2: note: in expansion of macro ‘_compiletime_assert’
  394 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
   50 |  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
      |  ^~~~~~~~~~~~~~~~
./include/linux/mlx5/device.h:75:2: note: in expansion of macro ‘BUILD_BUG_ON’
   75 |  BUILD_BUG_ON(__mlx5_st_sz_bits(typ) % 32);             \
      |  ^~~~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/port.c:794:2: note: in expansion of macro ‘MLX5_SET’
  794 |  MLX5_SET(pcmr_reg, in, local_port, 1);
      |  ^~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/port.c: In function ‘mlx5_set_port_fcs’:
./include/linux/compiler.h:394:38: error: call to ‘__compiletime_assert_776’ declared with attribute error: BUILD_BUG_ON failed: __mlx5_st_sz_bits(pcmr_reg) % 32
  394 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                      ^
./include/linux/compiler.h:375:4: note: in definition of macro ‘__compiletime_assert’
  375 |    prefix ## suffix();    \
      |    ^~~~~~
./include/linux/compiler.h:394:2: note: in expansion of macro ‘_compiletime_assert’
  394 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
   50 |  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
      |  ^~~~~~~~~~~~~~~~
./include/linux/mlx5/device.h:75:2: note: in expansion of macro ‘BUILD_BUG_ON’
   75 |  BUILD_BUG_ON(__mlx5_st_sz_bits(typ) % 32);             \
      |  ^~~~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/port.c:815:2: note: in expansion of macro ‘MLX5_SET’
  815 |  MLX5_SET(pcmr_reg, in, local_port, 1);
      |  ^~~~~~~~
./include/linux/compiler.h:394:38: error: call to ‘__compiletime_assert_777’ declared with attribute error: BUILD_BUG_ON failed: __mlx5_st_sz_bits(pcmr_reg) % 32
  394 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |                                      ^
./include/linux/compiler.h:375:4: note: in definition of macro ‘__compiletime_assert’
  375 |    prefix ## suffix();    \
      |    ^~~~~~
./include/linux/compiler.h:394:2: note: in expansion of macro ‘_compiletime_assert’
  394 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |  ^~~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
./include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
   50 |  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
      |  ^~~~~~~~~~~~~~~~
./include/linux/mlx5/device.h:75:2: note: in expansion of macro ‘BUILD_BUG_ON’
   75 |  BUILD_BUG_ON(__mlx5_st_sz_bits(typ) % 32);             \
      |  ^~~~~~~~~~~~
drivers/net/ethernet/mellanox/mlx5/core/port.c:816:2: note: in expansion of macro ‘MLX5_SET’
  816 |  MLX5_SET(pcmr_reg, in, fcs_chk, enable);
      |  ^~~~~~~~
scripts/Makefile.build:272: recipe for target 'drivers/net/ethernet/mellanox/mlx5/core/port.o' failed

See flexible-array conversions issue.

[GustavoARSilva]

Duplicate of https://github.com/KSPP/linux/issues/65