netdev - [PATCH] bpf: use flexible array members, not zero-length

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Message-Id: <20190928144814.27002-1-steve@sk2.org>
Date:   Sat, 28 Sep 2019 16:48:14 +0200
From:   Stephen Kitt <steve@....org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Cc:     linux-doc@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org,
        "Gustavo A . R . Silva" <gustavo@...eddedor.com>,
        Stephen Kitt <steve@....org>
Subject: [PATCH] bpf: use flexible array members, not zero-length

This switches zero-length arrays in variable-length structs to C99
flexible array members. GCC will then ensure that the arrays are
always the last element in the struct.

Coccinelle:
@@
identifier S, fld;
type T;
@@

struct S {
  ...
- T fld[0];
+ T fld[];
  ...
};

Signed-off-by: Stephen Kitt <steve@....org>
---
 Documentation/bpf/btf.rst       | 2 +-
 tools/lib/bpf/libbpf.c          | 2 +-
 tools/lib/bpf/libbpf_internal.h | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/bpf/btf.rst b/Documentation/bpf/btf.rst
index 4d565d202ce3..24ce50fc1fc1 100644
--- a/Documentation/bpf/btf.rst
+++ b/Documentation/bpf/btf.rst
@@ -670,7 +670,7 @@ func_info for each specific ELF section.::
         __u32   sec_name_off; /* offset to section name */
         __u32   num_info;
         /* Followed by num_info * record_size number of bytes */
-        __u8    data[0];
+        __u8    data[];
      };
 
 Here, num_info must be greater than 0.
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index e0276520171b..c02ea0e1a588 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -5577,7 +5577,7 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
 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 2e83a34f8c79..26eaa3f594aa 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -86,7 +86,7 @@ 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 */
-- 
2.20.1