sparc64: Replace zero-length array with flexible-array

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>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/sparc/kernel/cpumap.c b/arch/sparc/kernel/cpumap.c
index 1cb62bfeaa1ff8dd0777f2834991cc65d353fc99..f07ea88a83af3126cc87eb9dc5f36033ca4e3cd9 100644 (file)
--- a/arch/sparc/kernel/cpumap.c
+++ b/arch/sparc/kernel/cpumap.c
@@ -50,7 +50,7 @@ struct cpuinfo_tree {
 
        /* Offsets into nodes[] for each level of the tree */
        struct cpuinfo_level level[CPUINFO_LVL_MAX];
-       struct cpuinfo_node  nodes[0];
+       struct cpuinfo_node  nodes[];
 };
 
 

diff --git a/arch/sparc/kernel/ds.c b/arch/sparc/kernel/ds.c
index 75232cbd58bf520695fb1509397419520ae6d13e..522e5b51050c710bd22ef0d14dd672553f95ae0d 100644 (file)
--- a/arch/sparc/kernel/ds.c
+++ b/arch/sparc/kernel/ds.c
@@ -87,7 +87,7 @@ struct ds_reg_req {
        __u64                   handle;
        __u16                   major;
        __u16                   minor;
-       char                    svc_id[0];
+       char                    svc_id[];
 };
 
 struct ds_reg_ack {
@@ -701,12 +701,12 @@ struct ds_var_hdr {
 
 struct ds_var_set_msg {
        struct ds_var_hdr               hdr;
-       char                            name_and_value[0];
+       char                            name_and_value[];
 };
 
 struct ds_var_delete_msg {
        struct ds_var_hdr               hdr;
-       char                            name[0];
+       char                            name[];
 };
 
 struct ds_var_resp {
@@ -989,7 +989,7 @@ struct ds_queue_entry {
        struct ds_info                  *dp;
        int                             req_len;
        int                             __pad;
-       u64                             req[0];
+       u64                             req[];
 };
 
 static void process_ds_work(void)