| Message ID | 20200213000211.GA23171@embeddedor.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | b417107a659e9745f9ff905196ddff70cbe4eaa7 |
| Headers | show |
| Series | scsi: advansys: Replace zero-length array with flexible-array member | expand |
On Wed, Feb 12, 2020 at 06:02:11PM -0600, Gustavo A. R. Silva wrote: > Also, notice that, dynamic memory allocations won't be affected by > this change: Shouldn't you also convert this: asc_sg_head = kzalloc(sizeof(asc_scsi_q->sg_head) + use_sg * sizeof(struct asc_sg_list), GFP_ATOMIC); to use struct_size()?
On 2/12/20 19:14, Matthew Wilcox wrote: > On Wed, Feb 12, 2020 at 06:02:11PM -0600, Gustavo A. R. Silva wrote: >> Also, notice that, dynamic memory allocations won't be affected by >> this change: > > Shouldn't you also convert this: > asc_sg_head = kzalloc(sizeof(asc_scsi_q->sg_head) + > use_sg * sizeof(struct asc_sg_list), GFP_ATOMIC); > to use struct_size()? > It's not a requirement to do that prior to applying the change proposed by this patch. Thanks -- Gustavo
On 2/13/20 1:02 AM, 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> > --- > drivers/scsi/advansys.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c > index a242a62caaa1..c2c7850ff7b4 100644 > --- a/drivers/scsi/advansys.c > +++ b/drivers/scsi/advansys.c > @@ -316,7 +316,7 @@ typedef struct asc_sg_head { > ushort queue_cnt; > ushort entry_to_copy; > ushort res; > - ASC_SG_LIST sg_list[0]; > + ASC_SG_LIST sg_list[]; > } ASC_SG_HEAD; > > typedef struct asc_scsi_q { > Reviewed-by: Hannes Reinecke <hare@suse.de> Cheers, Hannes
Gustavo, > 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: Applied to 5.7/scsi-queue, thanks!
diff --git a/drivers/scsi/advansys.c b/drivers/scsi/advansys.c index a242a62caaa1..c2c7850ff7b4 100644 --- a/drivers/scsi/advansys.c +++ b/drivers/scsi/advansys.c @@ -316,7 +316,7 @@ typedef struct asc_sg_head { ushort queue_cnt; ushort entry_to_copy; ushort res; - ASC_SG_LIST sg_list[0]; + ASC_SG_LIST sg_list[]; } ASC_SG_HEAD; typedef struct asc_scsi_q {
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/scsi/advansys.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)