From: "Gustavo A. R. Silva" <gustavo@embeddedor.com> To: Eric Anholt <eric@anholt.net>, David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch> Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" <gustavo@embeddedor.com> Subject: [PATCH][next] drm/vc4/vc4_drv.h: Replace zero-length array with flexible-array member Date: Thu, 5 Mar 2020 04:57:07 -0600 [thread overview] Message-ID: <20200305105707.GA19261@embeddedor> (raw) The current codebase makes use of the zero-length array language extension to the C90 standard, 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. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> --- drivers/gpu/drm/vc4/vc4_drv.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h index f90c0d08e740..5ecb8b4a48a1 100644 --- a/drivers/gpu/drm/vc4/vc4_drv.h +++ b/drivers/gpu/drm/vc4/vc4_drv.h @@ -65,7 +65,7 @@ struct vc4_perfmon { * Note that counter values can't be reset, but you can fake a reset by * destroying the perfmon and creating a new one. */ - u64 counters[0]; + u64 counters[]; }; struct vc4_dev { -- 2.25.0
WARNING: multiple messages have this Message-ID (diff)
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com> To: Eric Anholt <eric@anholt.net>, David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch> Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, "Gustavo A. R. Silva" <gustavo@embeddedor.com> Subject: [PATCH][next] drm/vc4/vc4_drv.h: Replace zero-length array with flexible-array member Date: Thu, 5 Mar 2020 04:57:07 -0600 [thread overview] Message-ID: <20200305105707.GA19261@embeddedor> (raw) The current codebase makes use of the zero-length array language extension to the C90 standard, 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. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> --- drivers/gpu/drm/vc4/vc4_drv.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h index f90c0d08e740..5ecb8b4a48a1 100644 --- a/drivers/gpu/drm/vc4/vc4_drv.h +++ b/drivers/gpu/drm/vc4/vc4_drv.h @@ -65,7 +65,7 @@ struct vc4_perfmon { * Note that counter values can't be reset, but you can fake a reset by * destroying the perfmon and creating a new one. */ - u64 counters[0]; + u64 counters[]; }; struct vc4_dev { -- 2.25.0 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
next reply other threads:[~2020-03-05 10:54 UTC|newest] Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-03-05 10:57 Gustavo A. R. Silva [this message] 2020-03-05 10:57 ` [PATCH][next] drm/vc4/vc4_drv.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva 2020-03-06 10:50 ` Daniel Vetter 2020-03-06 10:50 ` Daniel Vetter
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