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@xxxxxxxxxx>
---
scripts/basic/fixdep.c | 2 +-
scripts/mod/modpost.c | 2 +-
scripts/mod/modpost.h | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index 877ca2c88246..d98540552941 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -160,7 +160,7 @@ struct item {
struct item *next;
unsigned int len;
unsigned int hash;
- char name[0];
+ char name[];
};
#define HASHSZ 256
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 5c3c50c5ec52..4d4b979d76be 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -166,7 +166,7 @@ struct symbol {
* (only for external modules) **/
unsigned int is_static:1; /* 1 if symbol is not global */
enum export export; /* Type of export */
- char name[0];
+ char name[];
};
static struct symbol *symbolhash[SYMBOL_HASH_SIZE];
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 60dca9b7106b..39f6c29fb568 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -111,7 +111,7 @@ buf_write(struct buffer *buf, const char *s, int len);
struct namespace_list {
struct namespace_list *next;
- char namespace[0];
+ char namespace[];
};
struct module {
