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Date:   Mon, 30 Sep 2019 06:07:47 +0000
From:   Song Liu <songliubraving@...com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
CC:     Stephen Kitt <steve@....org>, Alexei Starovoitov <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>,
        Martin Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>
Subject: Re: [PATCH] bpf: use flexible array members, not zero-length



> On Sep 28, 2019, at 10:49 PM, Gustavo A. R. Silva <gustavo@...eddedor.com> wrote:
> 
> 
> 
> On 9/28/19 09:48, Stephen Kitt wrote:
>> 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[];
> 
> I think you should preserve the tab here.

Agreed. 

Besides this:

Acked-by: Song Liu <songliubraving@...com>

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