diff options
| author | Gustavo A. R. Silva <gustavoars@kernel.org> | 2020-05-07 21:50:57 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2020-05-11 17:56:47 +0300 |
| commit | 385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0 (patch) | |
| tree | 46fe9e3745705302599a9e8fb89bf176bf755cf2 /tools | |
| parent | b4563facdcae55c83039d5efcc3b45a63da14d2f (diff) | |
| download | linux-385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0.tar.xz | |
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 'tools')
| -rw-r--r-- | tools/lib/bpf/libbpf.c | 2 | ||||
| -rw-r--r-- | tools/lib/bpf/libbpf_internal.h | 2 | ||||
| -rw-r--r-- | tools/testing/selftests/bpf/progs/core_reloc_types.h | 2 |
3 files changed, 3 insertions, 3 deletions
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 6c2f46908f4d..3da66540b54b 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -8352,7 +8352,7 @@ error: struct perf_sample_raw { struct perf_event_header header; uint32_t size; - char data[0]; + char data[]; }; struct perf_sample_lost { diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h index 8c3afbd97747..50d70e90d5f1 100644 --- a/tools/lib/bpf/libbpf_internal.h +++ b/tools/lib/bpf/libbpf_internal.h @@ -153,7 +153,7 @@ struct btf_ext_info_sec { __u32 sec_name_off; __u32 num_info; /* Followed by num_info * record_size number of bytes */ - __u8 data[0]; + __u8 data[]; }; /* The minimum bpf_func_info checked by the loader */ diff --git a/tools/testing/selftests/bpf/progs/core_reloc_types.h b/tools/testing/selftests/bpf/progs/core_reloc_types.h index 6d598cfbdb3e..34d84717c946 100644 --- a/tools/testing/selftests/bpf/progs/core_reloc_types.h +++ b/tools/testing/selftests/bpf/progs/core_reloc_types.h @@ -379,7 +379,7 @@ struct core_reloc_arrays___equiv_zero_sz_arr { struct core_reloc_arrays_substruct c[3]; struct core_reloc_arrays_substruct d[1][2]; /* equivalent to flexible array */ - struct core_reloc_arrays_substruct f[0][2]; + struct core_reloc_arrays_substruct f[][2]; }; struct core_reloc_arrays___fixed_arr { |