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| author |   Gustavo A. R. Silva <gustavoars@kernel.org> | 2020-05-07 13:50:57 -0500 |
|---|---|---|
| committer |   Daniel Borkmann <daniel@iogearbox.net> | 2020-05-11 16:56:47 +0200 |
| commit | 385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0 (patch) | |
| tree | 46fe9e3745705302599a9e8fb89bf176bf755cf2 /kernel/bpf | |
| parent | bpf, runqslower: include proper uapi/bpf.h (diff) | |
| download | linux-dev-385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0.tar.xz linux-dev-385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0.zip | |
bpf, libbpf: 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200507185057.GA13981@embeddedor
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/queue_stack_maps.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c index f697647ceb54..30e1373fd437 100644 --- a/kernel/bpf/queue_stack_maps.c +++ b/kernel/bpf/queue_stack_maps.c @@ -19,7 +19,7 @@ struct bpf_queue_stack { u32 head, tail; u32 size; /* max_entries + 1 */ - char elements[0] __aligned(8); + char elements[] __aligned(8); }; static struct bpf_queue_stack *bpf_queue_stack(struct bpf_map *map) |