| Message ID | 20200507185256.GA14313@embeddedor (mailing list archive) |
|---|---|
| State | Mainlined, archived |
| Headers | show |
| Series | fpga: dfl: Replace zero-length array with flexible-array | expand |
This looks like a a good change to me. Tested-by: Matthew Gerlach <matthew.gerlach@linux.intel.com> On Thu, 7 May 2020, 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] > > sizeof(flexible-array-member) triggers a warning because flexible array > members have incomplete type[1]. There are some instances of code in > which the sizeof operator is being incorrectly/erroneously applied to > zero-length arrays and the result is zero. Such instances may be hiding > some bugs. So, this work (flexible-array member conversions) will also > help to get completely rid of those sorts of issues. > > 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 <gustavoars@kernel.org> > --- > drivers/fpga/dfl.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h > index 9f0e656de720..1cd51ea52ce1 100644 > --- a/drivers/fpga/dfl.h > +++ b/drivers/fpga/dfl.h > @@ -235,7 +235,7 @@ struct dfl_feature_platform_data { > unsigned long dev_status; > void *private; > int num; > - struct dfl_feature features[0]; > + struct dfl_feature features[]; > }; > > static inline > >
I think Moritz had already applied it to his tree per last submission. https://lkml.org/lkml/2020/3/21/373 Thanks Hao > -----Original Message----- > From: matthew.gerlach@linux.intel.com <matthew.gerlach@linux.intel.com> > Sent: Saturday, May 9, 2020 2:21 AM > To: Gustavo A. R. Silva <gustavoars@kernel.org> > Cc: Wu, Hao <hao.wu@intel.com>; linux-fpga@vger.kernel.org; linux- > kernel@vger.kernel.org > Subject: Re: [PATCH] fpga: dfl: Replace zero-length array with flexible-array > > > > This looks like a a good change to me. > > Tested-by: Matthew Gerlach <matthew.gerlach@linux.intel.com> > > On Thu, 7 May 2020, 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] > > > > sizeof(flexible-array-member) triggers a warning because flexible array > > members have incomplete type[1]. There are some instances of code in > > which the sizeof operator is being incorrectly/erroneously applied to > > zero-length arrays and the result is zero. Such instances may be hiding > > some bugs. So, this work (flexible-array member conversions) will also > > help to get completely rid of those sorts of issues. > > > > 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 <gustavoars@kernel.org> > > --- > > drivers/fpga/dfl.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h > > index 9f0e656de720..1cd51ea52ce1 100644 > > --- a/drivers/fpga/dfl.h > > +++ b/drivers/fpga/dfl.h > > @@ -235,7 +235,7 @@ struct dfl_feature_platform_data { > > unsigned long dev_status; > > void *private; > > int num; > > - struct dfl_feature features[0]; > > + struct dfl_feature features[]; > > }; > > > > static inline > > > >
diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h index 9f0e656de720..1cd51ea52ce1 100644 --- a/drivers/fpga/dfl.h +++ b/drivers/fpga/dfl.h @@ -235,7 +235,7 @@ struct dfl_feature_platform_data { unsigned long dev_status; void *private; int num; - struct dfl_feature features[0]; + struct dfl_feature features[]; }; static inline
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] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. 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 <gustavoars@kernel.org> --- drivers/fpga/dfl.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)