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@xxxxxxxxxxx>
Signed-off-by: Antony Antony <antony.antony@xxxxxxxxxxx>
Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
---
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>
