| Message ID | 20200319212950.GA9155@embeddedor.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 56d8623cedf929bfb1385868e423b978d0e76eea |
| Delegated to: | Jiri Kosina |
| Headers | show |
| Series | [next] intel-ish-hid: ishtp: hbm.h: Replace zero-length array with flexible-array member | expand |
On Thu, 19 Mar 2020, 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/hid/intel-ish-hid/ishtp/hbm.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/hid/intel-ish-hid/ishtp/hbm.h b/drivers/hid/intel-ish-hid/ishtp/hbm.h > index bb85985b1620..7c445b203f2a 100644 > --- a/drivers/hid/intel-ish-hid/ishtp/hbm.h > +++ b/drivers/hid/intel-ish-hid/ishtp/hbm.h > @@ -82,7 +82,7 @@ struct ishtp_msg_hdr { > > struct ishtp_bus_message { > uint8_t hbm_cmd; > - uint8_t data[0]; > + uint8_t data[]; > } __packed; > > /** Applied this one too, thanks Gustavo.
On 3/20/20 6:08 PM, Jiri Kosina wrote: > > Applied this one too, thanks Gustavo. > Awesome. :) Thanks, Jiri. -- Gustavo
diff --git a/drivers/hid/intel-ish-hid/ishtp/hbm.h b/drivers/hid/intel-ish-hid/ishtp/hbm.h index bb85985b1620..7c445b203f2a 100644 --- a/drivers/hid/intel-ish-hid/ishtp/hbm.h +++ b/drivers/hid/intel-ish-hid/ishtp/hbm.h @@ -82,7 +82,7 @@ struct ishtp_msg_hdr { struct ishtp_bus_message { uint8_t hbm_cmd; - uint8_t data[0]; + uint8_t data[]; } __packed; /**
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/hid/intel-ish-hid/ishtp/hbm.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)