| Message ID | 9db60f061d1c577f14136f81af641f58bccbead3.1544187795.git.mchehab+samsung@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] media: cedrus: don't initialize pointers with zero | expand |
Hi, On Fri, 2018-12-07 at 08:03 -0500, Mauro Carvalho Chehab wrote: > A common mistake is to assume that initializing a var with: > struct foo f = { 0 }; > > Would initialize a zeroed struct. Actually, what this does is > to initialize the first element of the struct to zero. > > According to C99 Standard 6.7.8.21: > > "If there are fewer initializers in a brace-enclosed > list than there are elements or members of an aggregate, > or fewer characters in a string literal used to initialize > an array of known size than there are elements in the array, > the remainder of the aggregate shall be initialized implicitly > the same as objects that have static storage duration." > > So, in practice, it could zero the entire struct, but, if the > first element is not an integer, it will produce warnings: > > drivers/staging/media/sunxi/cedrus/cedrus.c:drivers/staging/media/sunxi/cedrus/cedrus.c:78:49: warning: Using plain integer as NULL pointer > drivers/staging/media/sunxi/cedrus/cedrus_dec.c:drivers/staging/media/sunxi/cedrus/cedrus_dec.c:29:35: warning: Using plain integer as NULL pointer > > As the right initialization would be, instead: > > struct foo f = { NULL }; Thanks for sharing these details, it's definitely interesting and good to know :) > Another way to initialize it with gcc is to use: > > struct foo f = {}; > > That seems to be a gcc extension, but clang also does the right thing, > and that's a clean way for doing it. > > Anyway, I decided to check upstream what's the most commonly pattern. > The "= {}" pattern has about 2000 entries: > > $ git grep -E "=\s*\{\s*\}"|wc -l > 1951 > > The standard-C compliant pattern has about 2500 entries: > > $ git grep -E "=\s*\{\s*NULL\s*\}"|wc -l > 137 > $ git grep -E "=\s*\{\s*0\s*\}"|wc -l > 2323 > > Meaning that developers have split options on that. > > So, let's opt to the simpler form. Acked-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com> > Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> > --- > drivers/staging/media/sunxi/cedrus/cedrus.c | 2 +- > drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c b/drivers/staging/media/sunxi/cedrus/cedrus.c > index b538eb0321d8..b7c918fa5fd1 100644 > --- a/drivers/staging/media/sunxi/cedrus/cedrus.c > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c > @@ -75,7 +75,7 @@ static int cedrus_init_ctrls(struct cedrus_dev *dev, struct cedrus_ctx *ctx) > memset(ctx->ctrls, 0, ctrl_size); > > for (i = 0; i < CEDRUS_CONTROLS_COUNT; i++) { > - struct v4l2_ctrl_config cfg = { 0 }; > + struct v4l2_ctrl_config cfg = {}; > > cfg.elem_size = cedrus_controls[i].elem_size; > cfg.id = cedrus_controls[i].id; > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c > index e40180a33951..f10c25f5460e 100644 > --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c > @@ -26,7 +26,7 @@ void cedrus_device_run(void *priv) > { > struct cedrus_ctx *ctx = priv; > struct cedrus_dev *dev = ctx->dev; > - struct cedrus_run run = { 0 }; > + struct cedrus_run run = {}; > struct media_request *src_req; > unsigned long flags; >
Em Fri, 07 Dec 2018 14:21:44 +0100 Paul Kocialkowski <paul.kocialkowski@bootlin.com> escreveu: > Hi, > > On Fri, 2018-12-07 at 08:03 -0500, Mauro Carvalho Chehab wrote: > > A common mistake is to assume that initializing a var with: > > struct foo f = { 0 }; > > > > Would initialize a zeroed struct. Actually, what this does is > > to initialize the first element of the struct to zero. > > > > According to C99 Standard 6.7.8.21: > > > > "If there are fewer initializers in a brace-enclosed > > list than there are elements or members of an aggregate, > > or fewer characters in a string literal used to initialize > > an array of known size than there are elements in the array, > > the remainder of the aggregate shall be initialized implicitly > > the same as objects that have static storage duration." > > > > So, in practice, it could zero the entire struct, but, if the > > first element is not an integer, it will produce warnings: > > > > drivers/staging/media/sunxi/cedrus/cedrus.c:drivers/staging/media/sunxi/cedrus/cedrus.c:78:49: warning: Using plain integer as NULL pointer > > drivers/staging/media/sunxi/cedrus/cedrus_dec.c:drivers/staging/media/sunxi/cedrus/cedrus_dec.c:29:35: warning: Using plain integer as NULL pointer > > > > As the right initialization would be, instead: > > > > struct foo f = { NULL }; > > Thanks for sharing these details, it's definitely interesting and good > to know :) Yeah, that's something that was bothering for quite a while, as I've seen patches using either one of the ways. It took me a while to do some research, and having it documented at the patch helps, as we should now handle it the same way for similar stuff :-) > > > Another way to initialize it with gcc is to use: > > > > struct foo f = {}; > > > > That seems to be a gcc extension, but clang also does the right thing, > > and that's a clean way for doing it. > > > > Anyway, I decided to check upstream what's the most commonly pattern. > > The "= {}" pattern has about 2000 entries: > > > > $ git grep -E "=\s*\{\s*\}"|wc -l > > 1951 > > > > The standard-C compliant pattern has about 2500 entries: > > > > $ git grep -E "=\s*\{\s*NULL\s*\}"|wc -l > > 137 > > $ git grep -E "=\s*\{\s*0\s*\}"|wc -l > > 2323 > > > > Meaning that developers have split options on that. > > > > So, let's opt to the simpler form. > > Acked-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com> Applied, thanks! > > > Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> > > --- > > drivers/staging/media/sunxi/cedrus/cedrus.c | 2 +- > > drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c b/drivers/staging/media/sunxi/cedrus/cedrus.c > > index b538eb0321d8..b7c918fa5fd1 100644 > > --- a/drivers/staging/media/sunxi/cedrus/cedrus.c > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c > > @@ -75,7 +75,7 @@ static int cedrus_init_ctrls(struct cedrus_dev *dev, struct cedrus_ctx *ctx) > > memset(ctx->ctrls, 0, ctrl_size); > > > > for (i = 0; i < CEDRUS_CONTROLS_COUNT; i++) { > > - struct v4l2_ctrl_config cfg = { 0 }; > > + struct v4l2_ctrl_config cfg = {}; > > > > cfg.elem_size = cedrus_controls[i].elem_size; > > cfg.id = cedrus_controls[i].id; > > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c > > index e40180a33951..f10c25f5460e 100644 > > --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c > > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c > > @@ -26,7 +26,7 @@ void cedrus_device_run(void *priv) > > { > > struct cedrus_ctx *ctx = priv; > > struct cedrus_dev *dev = ctx->dev; > > - struct cedrus_run run = { 0 }; > > + struct cedrus_run run = {}; > > struct media_request *src_req; > > unsigned long flags; > > Thanks, Mauro
diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c b/drivers/staging/media/sunxi/cedrus/cedrus.c index b538eb0321d8..b7c918fa5fd1 100644 --- a/drivers/staging/media/sunxi/cedrus/cedrus.c +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c @@ -75,7 +75,7 @@ static int cedrus_init_ctrls(struct cedrus_dev *dev, struct cedrus_ctx *ctx) memset(ctx->ctrls, 0, ctrl_size); for (i = 0; i < CEDRUS_CONTROLS_COUNT; i++) { - struct v4l2_ctrl_config cfg = { 0 }; + struct v4l2_ctrl_config cfg = {}; cfg.elem_size = cedrus_controls[i].elem_size; cfg.id = cedrus_controls[i].id; diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c index e40180a33951..f10c25f5460e 100644 --- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c +++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c @@ -26,7 +26,7 @@ void cedrus_device_run(void *priv) { struct cedrus_ctx *ctx = priv; struct cedrus_dev *dev = ctx->dev; - struct cedrus_run run = { 0 }; + struct cedrus_run run = {}; struct media_request *src_req; unsigned long flags;
A common mistake is to assume that initializing a var with: struct foo f = { 0 }; Would initialize a zeroed struct. Actually, what this does is to initialize the first element of the struct to zero. According to C99 Standard 6.7.8.21: "If there are fewer initializers in a brace-enclosed list than there are elements or members of an aggregate, or fewer characters in a string literal used to initialize an array of known size than there are elements in the array, the remainder of the aggregate shall be initialized implicitly the same as objects that have static storage duration." So, in practice, it could zero the entire struct, but, if the first element is not an integer, it will produce warnings: drivers/staging/media/sunxi/cedrus/cedrus.c:drivers/staging/media/sunxi/cedrus/cedrus.c:78:49: warning: Using plain integer as NULL pointer drivers/staging/media/sunxi/cedrus/cedrus_dec.c:drivers/staging/media/sunxi/cedrus/cedrus_dec.c:29:35: warning: Using plain integer as NULL pointer As the right initialization would be, instead: struct foo f = { NULL }; Another way to initialize it with gcc is to use: struct foo f = {}; That seems to be a gcc extension, but clang also does the right thing, and that's a clean way for doing it. Anyway, I decided to check upstream what's the most commonly pattern. The "= {}" pattern has about 2000 entries: $ git grep -E "=\s*\{\s*\}"|wc -l 1951 The standard-C compliant pattern has about 2500 entries: $ git grep -E "=\s*\{\s*NULL\s*\}"|wc -l 137 $ git grep -E "=\s*\{\s*0\s*\}"|wc -l 2323 Meaning that developers have split options on that. So, let's opt to the simpler form. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> --- drivers/staging/media/sunxi/cedrus/cedrus.c | 2 +- drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)