linux-kernel - Re: [PATCH] drm/amdgpu/smu10: Replace one-element array and use struct_size() helper

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Date:   Wed, 20 May 2020 14:17:40 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Christian König <christian.koenig@....com>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Evan Quan <evan.quan@....com>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amdgpu/smu10: Replace one-element array and use
 struct_size() helper

Applied.  thanks!

Alex

On Wed, May 20, 2020 at 3:42 AM Christian König
<christian.koenig@....com> wrote:
>
> Am 20.05.20 um 00:55 schrieb Gustavo A. R. Silva:
> > The current codebase makes use of one-element arrays in the following
> > form:
> >
> > struct something {
> >      int length;
> >      u8 data[1];
> > };
> >
> > struct something *instance;
> >
> > instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> > instance->length = size;
> > memcpy(instance->data, source, size);
> >
> > but the preferred mechanism to declare variable-length types such as
> > these ones is a flexible array member[1][2], introduced in C99:
> >
> > struct foo {
> >          int stuff;
> >          struct boo array[];
> > };
> >
> > By making use of the mechanism above, we will get a compiler warning
> > in case the flexible array does not occur last in the structure, which
> > will help us prevent some kind of undefined behavior bugs from being
> > inadvertently introduced[3] to the codebase from now on. So, replace
> > the one-element array with a flexible-array member.
> >
> > Also, make use of the new struct_size() helper to properly calculate the
> > size of struct smu10_voltage_dependency_table.
> >
> > This issue was found with the help of Coccinelle and, audited and fixed
> > _manually_.
> >
> > [1] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.gnu.org%2Fonlinedocs%2Fgcc%2FZero-Length.html&amp;data=02%7C01%7Cchristian.koenig%40amd.com%7C8a400bdb88924a1d951508d7fc471966%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637255254622039268&amp;sdata=ILOPPn17c%2B3oyLLdh%2BgH2b%2B8RdhWuTFGxruRD7GUHOo%3D&amp;reserved=0
> > [2] https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2FKSPP%2Flinux%2Fissues%2F21&amp;data=02%7C01%7Cchristian.koenig%40amd.com%7C8a400bdb88924a1d951508d7fc471966%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637255254622039268&amp;sdata=lCr5Otij55Snq27BDp4RmtW4hNhOS%2Bm4vSUOOAz07XA%3D&amp;reserved=0
> > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>
> Acked-by: Christian König <christian.koenig@....com>
>
> May I suggest that we add a section how to correctly do this to
> Documentation/process/coding-style.rst or similar document?
>
> I've seen a bunch of different approaches and some even doesn't work
> with some gcc versions and result in a broken binary.
>
> Thanks,
> Christian.
>
> > ---
> >   drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.c | 6 ++----
> >   drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.h | 2 +-
> >   2 files changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.c b/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.c
> > index 246bb9ac557d8..c9cfe90a29471 100644
> > --- a/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.c
> > +++ b/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.c
> > @@ -410,12 +410,10 @@ static int smu10_get_clock_voltage_dependency_table(struct pp_hwmgr *hwmgr,
> >                       struct smu10_voltage_dependency_table **pptable,
> >                       uint32_t num_entry, const DpmClock_t *pclk_dependency_table)
> >   {
> > -     uint32_t table_size, i;
> > +     uint32_t i;
> >       struct smu10_voltage_dependency_table *ptable;
> >
> > -     table_size = sizeof(uint32_t) + sizeof(struct smu10_voltage_dependency_table) * num_entry;
> > -     ptable = kzalloc(table_size, GFP_KERNEL);
> > -
> > +     ptable = kzalloc(struct_size(ptable, entries, num_entry), GFP_KERNEL);
> >       if (NULL == ptable)
> >               return -ENOMEM;
> >
> > diff --git a/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.h b/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.h
> > index 1fb296a996f3a..0f969de10fabc 100644
> > --- a/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.h
> > +++ b/drivers/gpu/drm/amd/powerplay/hwmgr/smu10_hwmgr.h
> > @@ -192,7 +192,7 @@ struct smu10_clock_voltage_dependency_record {
> >
> >   struct smu10_voltage_dependency_table {
> >       uint32_t count;
> > -     struct smu10_clock_voltage_dependency_record entries[1];
> > +     struct smu10_clock_voltage_dependency_record entries[];
> >   };
> >
> >   struct smu10_clock_voltage_information {
>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx@...ts.freedesktop.org
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