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authorGustavo A. R. Silva <gustavoars@kernel.org>2020-05-07 13:50:57 -0500
committerDaniel Borkmann <daniel@iogearbox.net>2020-05-11 16:56:47 +0200
commit385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0 (patch)
tree46fe9e3745705302599a9e8fb89bf176bf755cf2 /tools/lib
parentb4563facdcae55c83039d5efcc3b45a63da14d2f (diff)
downloadlinux-385bbf7b119a4feb6d6bcf3586f1bb1dd9c5b0a0.tar.bz2
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/lib')
-rw-r--r--tools/lib/bpf/libbpf.c2
-rw-r--r--tools/lib/bpf/libbpf_internal.h2
2 files changed, 2 insertions, 2 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 */