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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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 14:23:02 -05:00 committed by David S. Miller
parent 57829ea468
commit 60da7d0bc7
2 changed files with 5 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/sparc/kernel/cpumap.c
View File

@ -50,7 +50,7 @@ struct cpuinfo_tree {
/* Offsets into nodes[] for each level of the tree */ /* Offsets into nodes[] for each level of the tree */
struct cpuinfo_level level[CPUINFO_LVL_MAX]; struct cpuinfo_level level[CPUINFO_LVL_MAX];
struct cpuinfo_node nodes[0]; struct cpuinfo_node nodes[];
}; };

8
arch/sparc/kernel/ds.c
View File

@ -87,7 +87,7 @@ struct ds_reg_req {
__u64 handle; __u64 handle;
__u16 major; __u16 major;
__u16 minor; __u16 minor;
char svc_id[0]; char svc_id[];
}; };
struct ds_reg_ack { struct ds_reg_ack {
@ -701,12 +701,12 @@ struct ds_var_hdr {
struct ds_var_set_msg { struct ds_var_set_msg {
struct ds_var_hdr hdr; struct ds_var_hdr hdr;
char name_and_value[0]; char name_and_value[];
}; };
struct ds_var_delete_msg { struct ds_var_delete_msg {
struct ds_var_hdr hdr; struct ds_var_hdr hdr;
char name[0]; char name[];
}; };
struct ds_var_resp { struct ds_var_resp {
@ -989,7 +989,7 @@ struct ds_queue_entry {
struct ds_info *dp; struct ds_info *dp;
int req_len; int req_len;
int __pad; int __pad;
u64 req[0]; u64 req[];
}; };
static void process_ds_work(void) static void process_ds_work(void)