Re: [PATCH ipsec-next v1 6/7] bpf: selftests: test_tunnel: Disable CO-RE relocations

On 11/22/23 1:20 PM, Daniel Xu wrote:

Switching to vmlinux.h definitions seems to make the verifier very unhappy with bitfield accesses. The error is:

 ; md.u.md2.dir = direction;
 33: (69) r1 = *(u16 *)(r2 +11)
 misaligned stack access off (0x0; 0x0)+-64+11 size 2

It looks like disabling CO-RE relocations seem to make the error go away.

Thanks for reporting. I did some preliminary investigation and the failure is due to that we do not support CORE-based bitfield store yet. Besides disabling CORE-relocation as in this patch, there are a few ways to do this: - Change the code to avoid bitfield store and use 1/2/4/8 byte(s) store. A little bit ugly but it should work. - Use to-be-supported 'preserve_static_offset' (https://reviews.llvm.org/D133361) to preserve the offset. This might work (I didn't try it yet). - Eduard did some early study trying to remove CORE attribute (preserve_access_index) from UAPI structures. In this particular case, erspan_metadata is in /usr/include/linux/erspan.h.

We will also investigate whether we could store bitfield store directly with CORE.

Co-developed-by: Antony Antony antony.antony@secunet.com Signed-off-by: Antony Antony antony.antony@secunet.com Signed-off-by: Daniel Xu dxu@dxuuu.xyz

---

tools/testing/selftests/bpf/progs/test_tunnel_kern.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/tools/testing/selftests/bpf/progs/test_tunnel_kern.c b/tools/testing/selftests/bpf/progs/test_tunnel_kern.c index 3065a716544d..ec7e04e012ae 100644 --- a/tools/testing/selftests/bpf/progs/test_tunnel_kern.c +++ b/tools/testing/selftests/bpf/progs/test_tunnel_kern.c @@ -6,6 +6,7 @@

• modify it under the terms of version 2 of the GNU General Public
• License as published by the Free Software Foundation.

*/ +#define BPF_NO_PRESERVE_ACCESS_INDEX

This is a temporary workaround and hopefully we can lift it in the near future. Please add a comment here with prefix 'Workaround' to explain why this is needed and later on we can earliy search the keyword and remember to tackle this.

#include "vmlinux.h" #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h>