| Message ID | 20200319184838.GA25767@embeddedor.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 0a8cdc8b14ef9f4474d38f0c364c82515798ade0 |
| Headers | show |
| Series | thermal: qcom: tsens.h: Replace zero-length array with flexible-array member | expand |
On Fri, Mar 20, 2020 at 12:18 AM Gustavo A. R. Silva <gustavo@embeddedor.com> wrote: > > 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> Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org> > --- > drivers/thermal/qcom/tsens.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/thermal/qcom/tsens.h b/drivers/thermal/qcom/tsens.h > index e24a865fbc34..92503712596a 100644 > --- a/drivers/thermal/qcom/tsens.h > +++ b/drivers/thermal/qcom/tsens.h > @@ -488,7 +488,7 @@ struct tsens_priv { > struct dentry *debug_root; > struct dentry *debug; > > - struct tsens_sensor sensor[0]; > + struct tsens_sensor sensor[]; > }; > > char *qfprom_read(struct device *dev, const char *cname); > -- > 2.23.0 >
On 19/03/2020 19:48, Gustavo A. R. Silva wrote: > 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> Applied, thanks > --- > drivers/thermal/qcom/tsens.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/thermal/qcom/tsens.h b/drivers/thermal/qcom/tsens.h > index e24a865fbc34..92503712596a 100644 > --- a/drivers/thermal/qcom/tsens.h > +++ b/drivers/thermal/qcom/tsens.h > @@ -488,7 +488,7 @@ struct tsens_priv { > struct dentry *debug_root; > struct dentry *debug; > > - struct tsens_sensor sensor[0]; > + struct tsens_sensor sensor[]; > }; > > char *qfprom_read(struct device *dev, const char *cname); >
diff --git a/drivers/thermal/qcom/tsens.h b/drivers/thermal/qcom/tsens.h index e24a865fbc34..92503712596a 100644 --- a/drivers/thermal/qcom/tsens.h +++ b/drivers/thermal/qcom/tsens.h @@ -488,7 +488,7 @@ struct tsens_priv { struct dentry *debug_root; struct dentry *debug; - struct tsens_sensor sensor[0]; + struct tsens_sensor sensor[]; }; char *qfprom_read(struct device *dev, const char *cname);
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/thermal/qcom/tsens.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)