> On Feb 11, 2022, at 3:54 PM, Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> On Thu, 10 Feb 2022 17:49:15 -0800 Song Liu wrote:
>> bpf_prog_pack causes build error with powerpc ppc64_defconfig:
>>
>> kernel/bpf/core.c:830:23: error: variably modified 'bitmap' at file scope
>> 830 | unsigned long bitmap[BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)];
>> | ^~~~~~
>
> No idea what this error means but...
v2 (which has applied to bpf-next) has more information about this.
Basically, BPF_PROG_CHUNK_COUNT contains a global variable for ppc.
>
>> Fix it by turning bitmap into a 0-length array.
>>
>> Fixes: 57631054fae6 ("bpf: Introduce bpf_prog_pack allocator")
>> Reported-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
>> Signed-off-by: Song Liu <song@xxxxxxxxxx>
>> ---
>> kernel/bpf/core.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>> index 42d96549a804..44623c9b5bb1 100644
>> --- a/kernel/bpf/core.c
>> +++ b/kernel/bpf/core.c
>> @@ -827,7 +827,7 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
>> struct bpf_prog_pack {
>> struct list_head list;
>> void *ptr;
>> - unsigned long bitmap[BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)];
>> + unsigned long bitmap[];
>
> This is really asking to be DECLARE_BITMAP(), does that fix the issue?
I am afraid DECLARE_BITMAP() will hit the same error here.
>
>> };
>>
>> #define BPF_PROG_MAX_PACK_PROG_SIZE BPF_PROG_PACK_SIZE
>> @@ -840,7 +840,7 @@ static struct bpf_prog_pack *alloc_new_pack(void)
>> {
>> struct bpf_prog_pack *pack;
>>
>> - pack = kzalloc(sizeof(*pack), GFP_KERNEL);
>> + pack = kzalloc(sizeof(*pack) + BITS_TO_BYTES(BPF_PROG_CHUNK_COUNT), GFP_KERNEL);
>
> Otherwise you may want to use struct_size(pack, bitmap, BITS...).
> One of the bots will soon send us a patch to do that.
Since v2 has applied to bpf-next, I will send another follow-up patch to
use struct_size, unless some bot get it first.
Thanks,
Song
