Gustavo A. R. Silva
2020-Mar-02 23:57 UTC
[Ocfs2-devel] [PATCH] ocfs2: Replace zero-length array with flexible-array member
Hi all, Friendly ping: Who can take this? Thanks -- Gustavo On 2/13/20 10:02, 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!KeuD5UeTm4D1RuZqlBVvBffhBRNEEwJOBI8LdMGIuVeEYbe0bDBSBxhjTSSTAQswDk2rEQ$ > [2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!KeuD5UeTm4D1RuZqlBVvBffhBRNEEwJOBI8LdMGIuVeEYbe0bDBSBxhjTSSTAQuwAeng5Q$ > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com> > --- > fs/ocfs2/journal.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c > index 68ba354cf361..b425f0b01dce 100644 > --- a/fs/ocfs2/journal.c > +++ b/fs/ocfs2/journal.c > @@ -91,7 +91,7 @@ enum ocfs2_replay_state { > struct ocfs2_replay_map { > unsigned int rm_slots; > enum ocfs2_replay_state rm_state; > - unsigned char rm_replay_slots[0]; > + unsigned char rm_replay_slots[]; > }; > > static void ocfs2_replay_map_set_state(struct ocfs2_super *osb, int state) >
Joseph Qi
2020-Mar-03 01:17 UTC
[Ocfs2-devel] [PATCH] ocfs2: Replace zero-length array with flexible-array member
Sorry for the late replay since I've missed the original mail. This patch looks good to me. Acked-by: Joseph Qi <joseph.qi at linux.alibaba.com> On 2020/3/3 07:57, Gustavo A. R. Silva wrote:> Hi all, > > Friendly ping: Who can take this? > > Thanks > -- > Gustavo > > On 2/13/20 10:02, 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!IqIf1kXINaofUdjTQKfUAjzgxIXeGsrvqMv7P5eK_l094j-wNPLRzzZ6U0LKmQmDvBq4SA$ >> [2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!IqIf1kXINaofUdjTQKfUAjzgxIXeGsrvqMv7P5eK_l094j-wNPLRzzZ6U0LKmQmeutI_Bg$ >> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") >> >> Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com> >> --- >> fs/ocfs2/journal.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/ocfs2/journal.c b/fs/ocfs2/journal.c >> index 68ba354cf361..b425f0b01dce 100644 >> --- a/fs/ocfs2/journal.c >> +++ b/fs/ocfs2/journal.c >> @@ -91,7 +91,7 @@ enum ocfs2_replay_state { >> struct ocfs2_replay_map { >> unsigned int rm_slots; >> enum ocfs2_replay_state rm_state; >> - unsigned char rm_replay_slots[0]; >> + unsigned char rm_replay_slots[]; >> }; >> >> static void ocfs2_replay_map_set_state(struct ocfs2_super *osb, int state) >>