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modpost,fixdep: 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: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 13:56:01 -05:00 committed by Masahiro Yamada
parent 5967577231
commit 859c817501
3 changed files with 3 additions and 3 deletions
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2
scripts/basic/fixdep.c
View File

@ -160,7 +160,7 @@ struct item {
struct item *next; struct item *next;
unsigned int len; unsigned int len;
unsigned int hash; unsigned int hash;
char name[0]; char name[];
}; };
#define HASHSZ 256 #define HASHSZ 256

2
scripts/mod/modpost.c
View File

@ -166,7 +166,7 @@ struct symbol {
* (only for external modules) **/ * (only for external modules) **/
unsigned int is_static:1; /* 1 if symbol is not global */ unsigned int is_static:1; /* 1 if symbol is not global */
enum export export; /* Type of export */ enum export export; /* Type of export */
char name[0]; char name[];
}; };
static struct symbol *symbolhash[SYMBOL_HASH_SIZE]; static struct symbol *symbolhash[SYMBOL_HASH_SIZE];

2
scripts/mod/modpost.h
View File

@ -111,7 +111,7 @@ buf_write(struct buffer *buf, const char *s, int len);
struct namespace_list { struct namespace_list {
struct namespace_list *next; struct namespace_list *next;
char namespace[0]; char namespace[];
}; };
struct module { struct module {