| Message ID | 20200507185138.GA14076@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | libceph: Replace zero-length array with flexible-array | expand |
On Thu, May 7, 2020 at 8:47 PM Gustavo A. R. Silva <gustavoars@kernel.org> 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> > --- > include/linux/ceph/mon_client.h | 2 +- > include/linux/crush/crush.h | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/ceph/mon_client.h b/include/linux/ceph/mon_client.h > index dbb8a6959a73..ce4ffeb384d7 100644 > --- a/include/linux/ceph/mon_client.h > +++ b/include/linux/ceph/mon_client.h > @@ -19,7 +19,7 @@ struct ceph_monmap { > struct ceph_fsid fsid; > u32 epoch; > u32 num_mon; > - struct ceph_entity_inst mon_inst[0]; > + struct ceph_entity_inst mon_inst[]; > }; > > struct ceph_mon_client; > diff --git a/include/linux/crush/crush.h b/include/linux/crush/crush.h > index 54741295c70b..38b0e4d50ed9 100644 > --- a/include/linux/crush/crush.h > +++ b/include/linux/crush/crush.h > @@ -87,7 +87,7 @@ struct crush_rule_mask { > struct crush_rule { > __u32 len; > struct crush_rule_mask mask; > - struct crush_rule_step steps[0]; > + struct crush_rule_step steps[]; > }; > > #define crush_rule_size(len) (sizeof(struct crush_rule) + \ > Applied. Thanks, Ilya
diff --git a/include/linux/ceph/mon_client.h b/include/linux/ceph/mon_client.h index dbb8a6959a73..ce4ffeb384d7 100644 --- a/include/linux/ceph/mon_client.h +++ b/include/linux/ceph/mon_client.h @@ -19,7 +19,7 @@ struct ceph_monmap { struct ceph_fsid fsid; u32 epoch; u32 num_mon; - struct ceph_entity_inst mon_inst[0]; + struct ceph_entity_inst mon_inst[]; }; struct ceph_mon_client; diff --git a/include/linux/crush/crush.h b/include/linux/crush/crush.h index 54741295c70b..38b0e4d50ed9 100644 --- a/include/linux/crush/crush.h +++ b/include/linux/crush/crush.h @@ -87,7 +87,7 @@ struct crush_rule_mask { struct crush_rule { __u32 len; struct crush_rule_mask mask; - struct crush_rule_step steps[0]; + struct crush_rule_step steps[]; }; #define crush_rule_size(len) (sizeof(struct crush_rule) + \
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> --- include/linux/ceph/mon_client.h | 2 +- include/linux/crush/crush.h | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)