linux-kernel - Re: [PATCH][next] drm/i915/guc: Replace zero-length arrays with flexible-array members

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Message-ID: <Y728SwYZeThQzohb@intel.com>
Date:   Tue, 10 Jan 2023 14:28:11 -0500
From:   Rodrigo Vivi <rodrigo.vivi@...el.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
CC:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...il.com>,
        "Daniel Vetter" <daniel@...ll.ch>,
        <intel-gfx@...ts.freedesktop.org>,
        <linux-hardening@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH][next] drm/i915/guc: Replace zero-length arrays with
 flexible-array members


On Tue, Jan 10, 2023 at 10:44:53AM -0600, Gustavo A. R. Silva wrote:
> Zero-length arrays are deprecated[1] and we are moving towards
> adopting C99 flexible-array members, instead. So, replace zero-length
> arrays in a couple of structures (three, actually) with flex-array
> members.
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
> routines on memcpy() and help us make progress towards globally
> enabling -fstrict-flex-arrays=3 [2].
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays [1]
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [2]
> Link: https://github.com/KSPP/linux/issues/78
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

> ---
>  drivers/gpu/drm/i915/gt/uc/guc_capture_fwif.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/guc_capture_fwif.h b/drivers/gpu/drm/i915/gt/uc/guc_capture_fwif.h
> index 3624abfd22d1..9d589c28f40f 100644
> --- a/drivers/gpu/drm/i915/gt/uc/guc_capture_fwif.h
> +++ b/drivers/gpu/drm/i915/gt/uc/guc_capture_fwif.h
> @@ -73,7 +73,7 @@ struct guc_debug_capture_list_header {
>  
>  struct guc_debug_capture_list {
>  	struct guc_debug_capture_list_header header;
> -	struct guc_mmio_reg regs[0];
> +	struct guc_mmio_reg regs[];
>  } __packed;
>  
>  /**
> @@ -125,7 +125,7 @@ struct guc_state_capture_header_t {
>  
>  struct guc_state_capture_t {
>  	struct guc_state_capture_header_t header;
> -	struct guc_mmio_reg mmio_entries[0];
> +	struct guc_mmio_reg mmio_entries[];
>  } __packed;
>  
>  enum guc_capture_group_types {
> @@ -145,7 +145,7 @@ struct guc_state_capture_group_header_t {
>  /* this is the top level structure where an error-capture dump starts */
>  struct guc_state_capture_group_t {
>  	struct guc_state_capture_group_header_t grp_header;
> -	struct guc_state_capture_t capture_entries[0];
> +	struct guc_state_capture_t capture_entries[];

Please notice we are currently using sizeof(struct ...).
Along with your proposed changes, shouldn't we also start using
the struct_size() which already take the flexible array into account?

>  } __packed;
>  
>  /**
> -- 
> 2.34.1
>