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authorGustavo A. R. Silva <gustavo@embeddedor.com>2020-03-23 21:30:22 -0500
committerGustavo A. R. Silva <gustavo@embeddedor.com>2020-04-18 15:44:56 -0500
commit6e88abb862898f55d083071e4423000983dcfe63 (patch)
tree50a16dc5580485af8e88062795edd61e866927bf
parentd6cdad870358128c1e753e6258e295ab8a5a2429 (diff)
uapi: linux: fiemap.h: 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") Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
-rw-r--r--include/uapi/linux/fiemap.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/uapi/linux/fiemap.h b/include/uapi/linux/fiemap.h
index 8c0bc24d5d95..7a900b2377b6 100644
--- a/include/uapi/linux/fiemap.h
+++ b/include/uapi/linux/fiemap.h
@@ -34,7 +34,7 @@ struct fiemap {
__u32 fm_mapped_extents;/* number of extents that were mapped (out) */
__u32 fm_extent_count; /* size of fm_extents array (in) */
__u32 fm_reserved;
- struct fiemap_extent fm_extents[0]; /* array of mapped extents (out) */
+ struct fiemap_extent fm_extents[]; /* array of mapped extents (out) */
};
#define FIEMAP_MAX_OFFSET (~0ULL)