On 11/25/23 7:54 PM, Alexei Starovoitov wrote:
On Sat, Nov 25, 2023 at 4:52 PM Yonghong Song yonghong.song@linux.dev wrote:
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.
I suspect we will forget to remove this "workaround" and people will start copy pasting it. Let's change the test instead to avoid bitfield access.
Agree. Avoiding bitfield access is definitely a solution. I just checked llvm preserve_static_offset (not merged yet), it seems to be able to fix the issue as well.
Applying patch https://reviews.llvm.org/D133361 to latest llvm-project, and with the following patch on top of patch 6,
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diff --git a/tools/testing/selftests/bpf/progs/test_tunnel_kern.c b/tools/testing/selftests/bpf/progs/test_tunnel_kern.c index ec7e04e012ae..11cbb12b4029 100644 --- a/tools/testing/selftests/bpf/progs/test_tunnel_kern.c +++ b/tools/testing/selftests/bpf/progs/test_tunnel_kern.c @@ -6,7 +6,10 @@ * 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 +#if __has_attribute(preserve_static_offset) +struct __attribute__((preserve_static_offset)) erspan_md2; +struct __attribute__((preserve_static_offset)) erspan_metadata; +#endif #include "vmlinux.h" #include <bpf/bpf_helpers.h> #include <bpf/bpf_endian.h> @@ -25,12 +28,12 @@ * 172.16.1.200 */ #define ASSIGNED_ADDR_VETH1 0xac1001c8
struct vxlanhdr { __be32 vx_flags; __be32 vx_vni; } __attribute__((packed));
int bpf_skb_set_fou_encap(struct __sk_buff *skb_ctx, struct bpf_fou_encap *encap, int type) __ksym; int bpf_skb_get_fou_encap(struct __sk_buff *skb_ctx, @@ -174,9 +177,13 @@ int erspan_set_tunnel(struct __sk_buff *skb) __u8 hwid = 7;
md.version = 2; +#if __has_attribute(preserve_static_offset) md.u.md2.dir = direction; md.u.md2.hwid = hwid & 0xf; md.u.md2.hwid_upper = (hwid >> 4) & 0x3; +#else + /* Change bit-field store to byte(s)-level stores. */ +#endif #endif
ret = bpf_skb_set_tunnel_opt(skb, &md, sizeof(md));
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Eduard, could you double check whether this is a valid use case to solve this kind of issue with preserve_static_offset attribute?