Re: [ndctl PATCH] ndctl/lib: move nd_cmd_pkg with a flex array to end of structures

[Dave Jiang <dave.jiang@intel.com>]

On 1/5/26 8:52 PM, Alison Schofield wrote:
> Placing nd_cmd_pkg anywhere but at the end of a structure can lead to
> undefined behavior for the flex array member. Move nd_cmd_pkg to the
> end of all affected structures.
> 
> Reproduce using Clang:
> ~/git/ndctl$ rm -rf build
> ~/git/ndctl$ CC=clang meson setup build
> ~/git/ndctl$ meson compile -C build
> 
> ../ndctl/lib/hpe1.h:324:20: warning: field 'gen' with variable sized type 'struct nd_cmd_pkg' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
> 
> Reported-by: Cristian Rodriguez <yo@cristianrodriguez.net>
> Closes: https://github.com/pmem/ndctl/issues/296
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

I wonder if a comment needs to be inserted to the definition of 'nd_cmd_pkg' to warn users that the struct should never be placed anywhere besides the end when used as a member of another struct.

> ---
>  ndctl/lib/hpe1.h      | 2 +-
>  ndctl/lib/hyperv.h    | 2 +-
>  ndctl/lib/intel.h     | 2 +-
>  ndctl/lib/msft.h      | 2 +-
>  ndctl/lib/papr.h      | 2 +-
>  ndctl/libndctl-nfit.h | 2 +-
>  6 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/ndctl/lib/hpe1.h b/ndctl/lib/hpe1.h
> index bc19f72ca8d0..99d8f57eb8e0 100644
> --- a/ndctl/lib/hpe1.h
> +++ b/ndctl/lib/hpe1.h
> @@ -321,8 +321,8 @@ union ndn_hpe1_cmd {
>  };
>  
>  struct ndn_pkg_hpe1 {
> -	struct nd_cmd_pkg gen;
>  	union ndn_hpe1_cmd u;
> +	struct nd_cmd_pkg gen;
>  } __attribute__((packed));
>  
>  #define NDN_IOCTL_HPE1_PASSTHRU		_IOWR(ND_IOCTL, ND_CMD_CALL, \
> diff --git a/ndctl/lib/hyperv.h b/ndctl/lib/hyperv.h
> index 45741c7cdd17..9157f1563632 100644
> --- a/ndctl/lib/hyperv.h
> +++ b/ndctl/lib/hyperv.h
> @@ -31,8 +31,8 @@ union nd_hyperv_cmd {
>  } __attribute__((packed));
>  
>  struct nd_pkg_hyperv {
> -	struct nd_cmd_pkg	gen;
>  	union  nd_hyperv_cmd	u;
> +	struct nd_cmd_pkg	gen;
>  } __attribute__((packed));
>  
>  #endif /* __NDCTL_HYPERV_H__ */
> diff --git a/ndctl/lib/intel.h b/ndctl/lib/intel.h
> index 5aee98062a84..09f8cf7745ce 100644
> --- a/ndctl/lib/intel.h
> +++ b/ndctl/lib/intel.h
> @@ -141,7 +141,6 @@ struct nd_intel_lss {
>  } __attribute__((packed));
>  
>  struct nd_pkg_intel {
> -	struct nd_cmd_pkg gen;
>  	union {
>  		struct nd_intel_smart smart;
>  		struct nd_intel_smart_inject inject;
> @@ -154,6 +153,7 @@ struct nd_pkg_intel {
>  		struct nd_intel_fw_finish_query fquery;
>  		struct nd_intel_lss lss;
>  	};
> +	struct nd_cmd_pkg gen;
>  };
>  
>  #define ND_INTEL_STATUS_MASK		0xffff
> diff --git a/ndctl/lib/msft.h b/ndctl/lib/msft.h
> index 8d246a5ed137..65789950abe1 100644
> --- a/ndctl/lib/msft.h
> +++ b/ndctl/lib/msft.h
> @@ -41,8 +41,8 @@ union ndn_msft_cmd {
>  } __attribute__((packed));
>  
>  struct ndn_pkg_msft {
> -	struct nd_cmd_pkg	gen;
>  	union ndn_msft_cmd	u;
> +	struct nd_cmd_pkg	gen;
>  } __attribute__((packed));
>  
>  #define NDN_MSFT_STATUS_MASK		0xffff
> diff --git a/ndctl/lib/papr.h b/ndctl/lib/papr.h
> index 77579396a7bd..4f35bc60017f 100644
> --- a/ndctl/lib/papr.h
> +++ b/ndctl/lib/papr.h
> @@ -8,8 +8,8 @@
>  
>  /* Wraps a nd_cmd generic header with pdsm header */
>  struct nd_pkg_papr {
> -	struct nd_cmd_pkg gen;
>  	struct nd_pkg_pdsm pdsm;
> +	struct nd_cmd_pkg gen;
>  };
>  
>  #endif /* __PAPR_H__ */
> diff --git a/ndctl/libndctl-nfit.h b/ndctl/libndctl-nfit.h
> index 9ec0db55776d..020dc7384a98 100644
> --- a/ndctl/libndctl-nfit.h
> +++ b/ndctl/libndctl-nfit.h
> @@ -77,13 +77,13 @@ struct nd_cmd_ars_err_inj_stat {
>  } __attribute__((packed));
>  
>  struct nd_cmd_bus {
> -	struct nd_cmd_pkg gen;
>  	union {
>  		struct nd_cmd_ars_err_inj_stat err_inj_stat;
>  		struct nd_cmd_ars_err_inj_clr err_inj_clr;
>  		struct nd_cmd_ars_err_inj err_inj;
>  		struct nd_cmd_translate_spa xlat_spa;
>  	};
> +	struct nd_cmd_pkg gen;
>  };
>  
>  int ndctl_bus_is_nfit_cmd_supported(struct ndctl_bus *bus, int cmd);