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SubjectRe: [PATCH 05/15] bpf: avoid gcc-10 stringop-overflow warning
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On 4/30/20 11:30 PM, Arnd Bergmann wrote:
> gcc-10 warns about accesses to zero-length arrays:
>
> kernel/bpf/core.c: In function 'bpf_patch_insn_single':
> cc1: warning: writing 8 bytes into a region of size 0 [-Wstringop-overflow=]
> In file included from kernel/bpf/core.c:21:
> include/linux/filter.h:550:20: note: at offset 0 to object 'insnsi' with size 0 declared here
> 550 | struct bpf_insn insnsi[0];
> | ^~~~~~
>
> In this case, we really want to have two flexible-array members,
> but that is not possible. Removing the union to make insnsi a
> flexible-array member while leaving insns as a zero-length array
> fixes the warning, as nothing writes to the other one in that way.
>
> This trick only works on linux-3.18 or higher, as older versions
> had additional members in the union.
>
> Fixes: 60a3b2253c41 ("net: bpf: make eBPF interpreter images read-only")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Not pretty but looks okay to me, both have the same offset afterwards
in the pahole dump as well.

struct bpf_prog {
[...]
unsigned int (*bpf_func)(const void *, const struct bpf_insn *); /* 48 8 */
struct sock_filter insns[0]; /* 56 0 */
struct bpf_insn insnsi[]; /* 56 0 */

/* size: 56, cachelines: 1, members: 21 */
/* sum members: 50, holes: 1, sum holes: 4 */
/* sum bitfield members: 10 bits, bit holes: 1, sum bit holes: 6 bits */
/* last cacheline: 56 bytes */
};

Applied to bpf-next, thanks!

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