[bpf-next,v4,0/3] Annotate kfuncs in .BTF_ids section

  === Description ===

This is a bpf-treewide change that annotates all kfuncs as such inside
BTF_ids. This annotation eventually allows us to automatically generate
kfunc prototypes from bpftool.

We store this metadata inside a yet-unused flags field inside struct
btf_id_set8 (thanks Kumar!). pahole will be taught where to look.

More details about the full chain of events are available in commit 3's
description.

The accompanying pahole and bpftool changes can be viewed
here on these "frozen" branches [0][1].

[0]: https://github.com/danobi/pahole/tree/kfunc_btf-v3-mailed
[1]: https://github.com/danobi/linux/tree/kfunc_bpftool-mailed

=== Changelog ===

Changes from v3:
* Rebase to bpf-next and add missing annotation on new kfunc

Changes from v2:
* Only WARN() for vmlinux kfuncs

Changes from v1:
* Move WARN_ON() up a call level
* Also return error when kfunc set is not properly tagged
* Use BTF_KFUNCS_START/END instead of flags
* Rename BTF_SET8_KFUNC to BTF_SET8_KFUNCS

Daniel Xu (3):
  bpf: btf: Support flags for BTF_SET8 sets
  bpf: btf: Add BTF_KFUNCS_START/END macro pair
  bpf: treewide: Annotate BPF kfuncs in BTF

 Documentation/bpf/kfuncs.rst                  |  8 +++----
 drivers/hid/bpf/hid_bpf_dispatch.c            |  8 +++----
 fs/verity/measure.c                           |  4 ++--
 include/linux/btf_ids.h                       | 21 +++++++++++++++----
 kernel/bpf/btf.c                              |  8 +++++++
 kernel/bpf/cpumask.c                          |  4 ++--
 kernel/bpf/helpers.c                          |  8 +++----
 kernel/bpf/map_iter.c                         |  4 ++--
 kernel/cgroup/rstat.c                         |  4 ++--
 kernel/trace/bpf_trace.c                      |  8 +++----
 net/bpf/test_run.c                            |  8 +++----
 net/core/filter.c                             | 20 +++++++++---------
 net/core/xdp.c                                |  4 ++--
 net/ipv4/bpf_tcp_ca.c                         |  4 ++--
 net/ipv4/fou_bpf.c                            |  4 ++--
 net/ipv4/tcp_bbr.c                            |  4 ++--
 net/ipv4/tcp_cubic.c                          |  4 ++--
 net/ipv4/tcp_dctcp.c                          |  4 ++--
 net/netfilter/nf_conntrack_bpf.c              |  4 ++--
 net/netfilter/nf_nat_bpf.c                    |  4 ++--
 net/xfrm/xfrm_interface_bpf.c                 |  4 ++--
 net/xfrm/xfrm_state_bpf.c                     |  4 ++--
 .../selftests/bpf/bpf_testmod/bpf_testmod.c   |  8 +++----
 23 files changed, 87 insertions(+), 66 deletions(-)
  

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Sun, 28 Jan 2024 18:24:05 -0700 you wrote:
> === Description ===
> 
> This is a bpf-treewide change that annotates all kfuncs as such inside
> .BTF_ids. This annotation eventually allows us to automatically generate
> kfunc prototypes from bpftool.
> 
> We store this metadata inside a yet-unused flags field inside struct
> btf_id_set8 (thanks Kumar!). pahole will be taught where to look.
> 
> [...]

Here is the summary with links:
  - [bpf-next,v4,1/3] bpf: btf: Support flags for BTF_SET8 sets
    https://git.kernel.org/bpf/bpf-next/c/79b47344bbc5
  - [bpf-next,v4,2/3] bpf: btf: Add BTF_KFUNCS_START/END macro pair
    https://git.kernel.org/bpf/bpf-next/c/2747e0ee57c2
  - [bpf-next,v4,3/3] bpf: treewide: Annotate BPF kfuncs in BTF
    https://git.kernel.org/bpf/bpf-next/c/6e7769e6419f

You are awesome, thank you!
  

On 2/3/24 19:45, Manu Bretelle wrote:
> On Sat, Feb 03, 2024 at 03:40:24PM +0100, Jiri Olsa wrote:
>> On Fri, Feb 02, 2024 at 03:09:05PM -0800, Manu Bretelle wrote:
>>> On Sun, Jan 28, 2024 at 06:24:05PM -0700, Daniel Xu wrote:
>>>> === Description ===
>>>>
>>>> This is a bpf-treewide change that annotates all kfuncs as such inside
>>>> .BTF_ids. This annotation eventually allows us to automatically generate
>>>> kfunc prototypes from bpftool.
>>>>
>>>> We store this metadata inside a yet-unused flags field inside struct
>>>> btf_id_set8 (thanks Kumar!). pahole will be taught where to look.
>>>>
>>>> More details about the full chain of events are available in commit 3's
>>>> description.
>>>>
>>>> The accompanying pahole and bpftool changes can be viewed
>>>> here on these "frozen" branches [0][1].
>>>>
>>>> [0]: https://github.com/danobi/pahole/tree/kfunc_btf-v3-mailed
>>>> [1]: https://github.com/danobi/linux/tree/kfunc_bpftool-mailed
>>>
>>>
>>> I hit a similar issue to [0] on master
>>> 943b043aeecc ("selftests/bpf: Fix bench runner SIGSEGV")
>>>  when cross-compiling on x86_64 (LE) to s390x (BE).
>>> I do have CONFIG_DEBUG_INFO_BTF enable and the issue would not trigger if
>>> I disabled CONFIG_DEBUG_INFO_BTF (and with the fix mentioned in [0]).
>>>
>>> What seems to happen is that `tools/resolve_btfids` is ran in the context of the
>>> host endianess and if I printk before the WARN_ON:
>>> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
>>> index ef380e546952..a9ed7a1a4936 100644
>>>   --- a/kernel/bpf/btf.c
>>>   +++ b/kernel/bpf/btf.c
>>>   @@ -8128,6 +8128,7 @@ int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
>>>            * WARN() for initcall registrations that do not check errors.
>>>            */
>>>           if (!(kset->set->flags & BTF_SET8_KFUNCS)) {
>>>   +        printk("Flag 0x%08X, expected 0x%08X\n", kset->set->flags, BTF_SET8_KFUNCS);
>>>                   WARN_ON(!kset->owner);
>>>                   return -EINVAL;
>>>           }
>>>
>>> the boot logs would show:
>>>   Flag 0x01000000, expected 0x00000001
>>>
>>> The issue did not happen prior to
>>> 6f3189f38a3e ("bpf: treewide: Annotate BPF kfuncs in BTF")
>>> has only 0 was written before.
>>>
>>> It seems [1] will be addressing cross-compilation, but it did not fix it as is
>>> by just applying on top of master, so probably some of the changes will also need
>>> to be ported to `tools/include/linux/btf_ids.h`?
>>
>> the fix in [1] is fixing flags in set8's pairs, but not the global flags
>>
>> it looks like Viktor's fix should now also swap that as well? like in the
>> change below on top of Viktor's changes (untested)
>>
>> jirka
>>
>>
>> ---
>> diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
>> index d01603ef6283..c44d57fec390 100644
>> --- a/tools/bpf/resolve_btfids/main.c
>> +++ b/tools/bpf/resolve_btfids/main.c
>> @@ -706,6 +706,8 @@ static int sets_patch(struct object *obj)
>>  			 * correctly translate everything.
>>  			 */
>>  			if (need_bswap) {
>> +				set8->flags = bswap_32(set8->flags);
>> +
>>  				for (i = 0; i < cnt; i++) {
>>  					set8->pairs[i].flags =
>>  						bswap_32(set8->pairs[i].flags);
>>
> 
> That should work. Here are a few tests I ran:
> 
> $ md5sum /tmp/kbuild-s390x/vmlinux.*
> eb658e51e089f3c5b2c8909a29dc9997  /tmp/kbuild-s390x/vmlinux.a
> # plain vmlinux before running resolv_btfids (all 0s)
> ea907cd46a1a73b8276b5f2a82af00ca  /tmp/kbuild-s390x/vmlinux.before_resolv
> # x86_64 resolv_btfids on master without Viktor's patch
> 980a40c3a3ff563d1c2d1ebdd5071a23  /tmp/kbuild-s390x/vmlinux.resolv_native
> # x86_64 resolv_btfids on master with Viktor's patch
> b986d19e242719ebea41c578235da662  /tmp/kbuild-s390x/vmlinux.resolv_native_patch_viktor
> # x86_64 resolv_btfids on master with Viktor's patch and your suggested patch
> 4edd8752ff01129945bd442689b1927b  /tmp/kbuild-s390x/vmlinux.resolv_native_patch_viktor_patched
> # s390x resolv_btfids run with qemu-s390x-static
> 4edd8752ff01129945bd442689b1927b  /tmp/kbuild-s390x/vmlinux.resolv_s390x
> 
> 
> and some hexdiff of those binaries:
> 
> 
> # difference between master's native build and s390x build.... has byte swapping for set8 and others
> diff -ruN <(xxd /tmp/kbuild-s390x/vmlinux.resolv_s390x) <(xxd /tmp/kbuild-s390x/vmlinux.resolv_native) > diff_s390x_native.diff
> https://gist.github.com/chantra/c3d58637a08a6f7340953dc155bb18cc
> 
> # difference betwee Viktor's version and  s390x build.... squinting my eyes I only see the global set8 is missing
> diff -ruN <(xxd /tmp/kbuild-s390x/vmlinux.resolv_s390x) <(xxd /tmp/kbuild-s390x/vmlinux.resolv_native_patch_viktor) > diff_s390x_native_viktor.diff
> https://gist.github.com/chantra/61cfff02b456ae72d3c0161ce1897097

Thanks for the testing Manu!

Jiri's suggested fix is now a part of [1].

Viktor

[1] https://lore.kernel.org/bpf/cover.1707157553.git.vmalik@redhat.com/

> 
> Have a good weekend all!
> 
> Manu
>