Messages in this thread | | | From | "Winkler, Tomas" <> | Subject | RE: [PATCH] treewide: Replace zero-length array with flexible-array | Date | Thu, 7 May 2020 20:08:40 +0000 |
| |
> -----Original Message----- > From: Gustavo A. R. Silva <gustavoars@kernel.org> > Sent: Thursday, May 07, 2020 21:54 > To: Winkler, Tomas <tomas.winkler@intel.com> > Cc: linux-kernel@vger.kernel.org > Subject: [PATCH] treewide: Replace zero-length array with flexible-array
Ack.
> > 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> > --- > samples/mei/mei-amt-version.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/samples/mei/mei-amt-version.c b/samples/mei/mei-amt-version.c > index 32234481ad7d..ad3e56042f96 100644 > --- a/samples/mei/mei-amt-version.c > +++ b/samples/mei/mei-amt-version.c > @@ -267,7 +267,7 @@ struct amt_host_if_msg_header { struct > amt_host_if_resp_header { > struct amt_host_if_msg_header header; > uint32_t status; > - unsigned char data[0]; > + unsigned char data[]; > } __attribute__((packed)); > > const uuid_le MEI_IAMTHIF = UUID_LE(0x12f80028, 0xb4b7, 0x4b2d, \
| |