The patch titled
Subject: mm: replace zero-length array with flexible-array member
has been added to the -mm tree. Its filename is
mm-replace-zero-length-array-with-flexible-array-member.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-replace-zero-length-array-with-flexible-array-member.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-replace-zero-length-array-with-flexible-array-member.patch
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From: chenqiwu <chenqiwu@xxxxxxxxxx>
Subject: mm: replace zero-length array with flexible-array member
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")
Link: http://lkml.kernel.org/r/1586599916-15456-1-git-send-email-qiwuchen55@xxxxxxxxx
Signed-off-by: chenqiwu <chenqiwu@xxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: Qian Cai <cai@xxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm.h | 2 +-
include/linux/mmzone.h | 2 +-
include/linux/swap.h | 2 +-
3 files changed, 3 insertions(+), 3 deletions(-)
--- a/include/linux/mm.h~mm-replace-zero-length-array-with-flexible-array-member
+++ a/include/linux/mm.h
@@ -1718,7 +1718,7 @@ struct frame_vector {
unsigned int nr_frames; /* Number of frames stored in ptrs array */
bool got_ref; /* Did we pin pages by getting page ref? */
bool is_pfns; /* Does array contain pages or pfns? */
- void *ptrs[0]; /* Array of pinned pfns / pages. Use
+ void *ptrs[]; /* Array of pinned pfns / pages. Use
* pfns_vector_pages() or pfns_vector_pfns()
* for access */
};
--- a/include/linux/mmzone.h~mm-replace-zero-length-array-with-flexible-array-member
+++ a/include/linux/mmzone.h
@@ -1147,7 +1147,7 @@ struct mem_section_usage {
DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION);
#endif
/* See declaration of similar field in struct zone */
- unsigned long pageblock_flags[0];
+ unsigned long pageblock_flags[];
};
void subsection_map_init(unsigned long pfn, unsigned long nr_pages);
--- a/include/linux/swap.h~mm-replace-zero-length-array-with-flexible-array-member
+++ a/include/linux/swap.h
@@ -275,7 +275,7 @@ struct swap_info_struct {
*/
struct work_struct discard_work; /* discard worker */
struct swap_cluster_list discard_clusters; /* discard clusters list */
- struct plist_node avail_lists[0]; /*
+ struct plist_node avail_lists[]; /*
* entries in swap_avail_heads, one
* entry per node.
* Must be last as the number of the
_
Patches currently in -mm which might be from chenqiwu@xxxxxxxxxx are
mm-swapfile-use-list_prevnext_entry-instead-of-open-coding.patch
mm-replace-zero-length-array-with-flexible-array-member.patch
