netdev - Re: [PATCH v2 bpf-next] libbpf: fix false uninitialized variable warning

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Message-ID: <327815ee-9a10-cab3-c8f8-8ceeafa0877f@iogearbox.net>
Date:   Thu, 30 Apr 2020 16:25:45 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jakub Sitnicki <jakub@...udflare.com>,
        Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH v2 bpf-next] libbpf: fix false uninitialized variable
 warning

On 4/30/20 10:13 AM, Jakub Sitnicki wrote:
> On Thu, Apr 30, 2020 at 04:14 AM CEST, Andrii Nakryiko wrote:
>> Some versions of GCC falsely detect that vi might not be initialized. That's
>> not true, but let's silence it with NULL initialization.
>>
>> Signed-off-by: Andrii Nakryiko <andriin@...com>
>> ---
>>   tools/lib/bpf/libbpf.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index d86ff8214b96..977add1b73e2 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -5003,8 +5003,8 @@ static int bpf_object__collect_map_relos(struct bpf_object *obj,
>>   					 GElf_Shdr *shdr, Elf_Data *data)
>>   {
>>   	int i, j, nrels, new_sz, ptr_sz = sizeof(void *);
>> +	const struct btf_var_secinfo *vi = NULL;
>>   	const struct btf_type *sec, *var, *def;
>> -	const struct btf_var_secinfo *vi;
>>   	const struct btf_member *member;
>>   	struct bpf_map *map, *targ_map;
>>   	const char *name, *mname;
> 
> Alternatively we could borrow the kernel uninitialized_var macro:
> 
> include/linux/compiler-clang.h:#define uninitialized_var(x) x = *(&(x))
> include/linux/compiler-gcc.h:#define uninitialized_var(x) x = x

We could do that potentially, at least to mark such locations explicitly,
although I wonder if it's not more churn than anything else adding the
infra for it. But generally no objections from my side.

Anyway, applied this one, thanks!