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Date:   Wed, 11 Jan 2023 04:16:24 -0500
From:   Rodrigo Vivi <rodrigo.vivi@intel.com>
To:     "Gustavo A. R. Silva" <gustavoars@kernel.org>
CC:     <dri-devel@lists.freedesktop.org>,
        <intel-gfx@lists.freedesktop.org>, <linux-kernel@vger.kernel.org>,
        <linux-hardening@vger.kernel.org>,
        "Daniel Vetter" <daniel@ffwll.ch>, David Airlie <airlied@gmail.com>
Subject: Re: [Intel-gfx] [PATCH][next] drm/i915/guc: Replace zero-length
 arrays with flexible-array members
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On Tue, Jan 10, 2023 at 01:42:57PM -0600, Gustavo A. R. Silva wrote:
> On Tue, Jan 10, 2023 at 02:28:11PM -0500, Rodrigo Vivi wrote:
> > 
> > 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@kernel.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 ...).
> 
> Yep; I noticed that. :)
> 
> > Along with your proposed changes, shouldn't we also start using
> > the struct_size() which already take the flexible array into account?
> 
> Not necessarily. In recent times, we don't include the struct_size
> changes in the same patch as the flex-array transformation. That's
> usually a follow-up patch.

okay, if that's not a problem, let's go with this for now and wait
for the follow ups.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

(and pushing it right now. Thanks for the patch)

> 
> --
> Gustavo