| Message ID | 20200228132323.GA20181@embeddedor (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next] sunrpc: Replace zero-length array with flexible-array member | expand |
On Fri, Feb 28, 2020 at 07:23:23AM -0600, 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] I don't understand the quoted sentences at all. But I assume you're telling me that sizeof(struct svc_deferred_req) won't be changed by this patch, so, good, applied. Thanks! --b. > > 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> > --- > include/linux/sunrpc/svc.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h > index 1afe38eb33f7..7f0a83451bc0 100644 > --- a/include/linux/sunrpc/svc.h > +++ b/include/linux/sunrpc/svc.h > @@ -380,7 +380,7 @@ struct svc_deferred_req { > struct cache_deferred_req handle; > size_t xprt_hlen; > int argslen; > - __be32 args[0]; > + __be32 args[]; > }; > > struct svc_process_info { > -- > 2.25.0
On 3/2/20 13:58, J. Bruce Fields wrote: > On Fri, Feb 28, 2020 at 07:23:23AM -0600, 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] > > I don't understand the quoted sentences at all. But I assume you're > telling me that sizeof(struct svc_deferred_req) won't be changed by this > patch, so, good, applied. Thanks! > Correct! :) Thanks -- Gustavo > --b. > >> >> 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> >> --- >> include/linux/sunrpc/svc.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h >> index 1afe38eb33f7..7f0a83451bc0 100644 >> --- a/include/linux/sunrpc/svc.h >> +++ b/include/linux/sunrpc/svc.h >> @@ -380,7 +380,7 @@ struct svc_deferred_req { >> struct cache_deferred_req handle; >> size_t xprt_hlen; >> int argslen; >> - __be32 args[0]; >> + __be32 args[]; >> }; >> >> struct svc_process_info { >> -- >> 2.25.0
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h index 1afe38eb33f7..7f0a83451bc0 100644 --- a/include/linux/sunrpc/svc.h +++ b/include/linux/sunrpc/svc.h @@ -380,7 +380,7 @@ struct svc_deferred_req { struct cache_deferred_req handle; size_t xprt_hlen; int argslen; - __be32 args[0]; + __be32 args[]; }; struct svc_process_info {
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> --- include/linux/sunrpc/svc.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)