On 2022/10/13 08:50, Martin KaFai Lau wrote:
> On 10/12/22 5:58 AM, Chengming Zhou wrote:
>> When tracing a kernel function with arg type is u32*, btf_ctx_access()
>> would report error: arg2 type INT is not a struct.
>>
>> The commit bb6728d75611 ("bpf: Allow access to int pointer arguments
>> in tracing programs") added support for int pointer, but don't skip
>> modifiers before checking it's type. This patch fixes it.
>
> A selftest is needed. You can refer to the selftest added in the patch set [0] of the commit bb6728d75611.
>
> This belongs to bpf-next. Please tag it as bpf-next and also v2 in the next revision:
> Documentation/bpf/bpf_devel_QA.rst (Q: How do I indicate which tree....)
>
> [0]: https://lore.kernel.org/bpf/20211208193245.172141-2-jolsa@xxxxxxxxxx/
Thanks for these helpful references, will do.
>
>>
>> Fixes: bb6728d75611 ("bpf: Allow access to int pointer arguments in tracing programs")
>> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>> ---
>> kernel/bpf/btf.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>> index eba603cec2c5..2b343c42ed10 100644
>> --- a/kernel/bpf/btf.c
>> +++ b/kernel/bpf/btf.c
>> @@ -5316,8 +5316,8 @@ static bool is_int_ptr(struct btf *btf, const struct btf_type *t)
>> /* t comes in already as a pointer */
>> t = btf_type_by_id(btf, t->type);
>> - /* allow const */
>> - if (BTF_INFO_KIND(t->info) == BTF_KIND_CONST)
>> + /* skip modifiers */
>> + while (btf_type_is_modifier(t))
>
> There is btf_type_skip_modifiers() that should be useful here.
Ok, will change to use this.
>
>> t = btf_type_by_id(btf, t->type);
>> return btf_type_is_int(t);
>
