Message ID | 20200319231058.GA18540@embeddedor.com |
---|---|
State | Accepted, archived |
Headers | show |
Series | [next] of: of_private.h: Replace zero-length array with flexible-array member | expand |
Context | Check | Description |
---|---|---|
robh/checkpatch | warning | "total: 0 errors, 1 warnings, 8 lines checked" |
On Thu, 19 Mar 2020 18:10:58 -0500, "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/of/of_private.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > Applied, thanks. Rob
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h index 207863c151a5..edc682249c00 100644 --- a/drivers/of/of_private.h +++ b/drivers/of/of_private.h @@ -24,7 +24,7 @@ struct alias_prop { const char *alias; struct device_node *np; int id; - char stem[0]; + char stem[]; }; #if defined(CONFIG_SPARC)
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/of/of_private.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)