[PATCH v2 bpf] selftests/bpf: fix static assert compilation issue for test_cls_*.c

[PATCH v2 bpf] selftests/bpf: fix static assert compilation issue for test_cls_*.c

[Alan Maguire]

commit bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")

...was backported to stable trees such as 5.15. The problem is that with older
LLVM/clang (14/15) - which is often used for older kernels - we see compilation
failures in BPF selftests now:

In file included from progs/test_cls_redirect_subprogs.c:2:
progs/test_cls_redirect.c:90:2: error: static assertion expression is not an integral constant expression
        sizeof(flow_ports_t) !=
        ^~~~~~~~~~~~~~~~~~~~~~~
progs/test_cls_redirect.c:91:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
                offsetofend(struct bpf_sock_tuple, ipv4.dport) -
                ^
progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
        (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
         ^
tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
                                 ^
In file included from progs/test_cls_redirect_subprogs.c:2:
progs/test_cls_redirect.c:95:2: error: static assertion expression is not an integral constant expression
        sizeof(flow_ports_t) !=
        ^~~~~~~~~~~~~~~~~~~~~~~
progs/test_cls_redirect.c:96:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
                offsetofend(struct bpf_sock_tuple, ipv6.dport) -
                ^
progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
        (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
         ^
tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
                                 ^
2 errors generated.
make: *** [Makefile:594: tools/testing/selftests/bpf/test_cls_redirect_subprogs.bpf.o] Error 1

The problem is the new offsetof() does not play nice with static asserts.
Given that the context is a static assert (and CO-RE relocation is not
needed at compile time), offsetof() usage can be replaced by restoring
the original offsetof() definition as __builtin_offsetof().

Fixes: bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")
Reported-by: Colm Harrington <colm.harrington@oracle.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

---
Changes since v1:

- simplified to restore offsetof() definition in test_cls_redirect.h,
  and added explanatory comment (Yonghong)
---
 tools/testing/selftests/bpf/progs/test_cls_redirect.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/test_cls_redirect.h b/tools/testing/selftests/bpf/progs/test_cls_redirect.h
index 76eab0aacba0..233b089d1fba 100644
--- a/tools/testing/selftests/bpf/progs/test_cls_redirect.h
+++ b/tools/testing/selftests/bpf/progs/test_cls_redirect.h
@@ -12,6 +12,15 @@
 #include <linux/ipv6.h>
 #include <linux/udp.h>
 
+/* offsetof() is used in static asserts, and the libbpf-redefined CO-RE
+ * friendly version breaks compilation for older clang versions <= 15
+ * when invoked in a static assert.  Restore original here.
+ */
+#ifdef offsetof
+#undef offsetof
+#define offsetof(type, member) __builtin_offsetof(type, member)
+#endif
+
 struct gre_base_hdr {
 	uint16_t flags;
 	uint16_t protocol;
-- 
2.39.3

Re: [PATCH v2 bpf] selftests/bpf: fix static assert compilation issue for test_cls_*.c

[Yipeng Zou]

在 2023/8/2 15:39, Alan Maguire 写道:
> commit bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")
>
> ...was backported to stable trees such as 5.15. The problem is that with older
> LLVM/clang (14/15) - which is often used for older kernels - we see compilation
> failures in BPF selftests now:
>
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:90:2: error: static assertion expression is not an integral constant expression
>          sizeof(flow_ports_t) !=
>          ^~~~~~~~~~~~~~~~~~~~~~~
> progs/test_cls_redirect.c:91:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
>                  offsetofend(struct bpf_sock_tuple, ipv4.dport) -
>                  ^
> progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
>          (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
>           ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
>                                   ^
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:95:2: error: static assertion expression is not an integral constant expression
>          sizeof(flow_ports_t) !=
>          ^~~~~~~~~~~~~~~~~~~~~~~
> progs/test_cls_redirect.c:96:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
>                  offsetofend(struct bpf_sock_tuple, ipv6.dport) -
>                  ^
> progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
>          (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
>           ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
>                                   ^
> 2 errors generated.
> make: *** [Makefile:594: tools/testing/selftests/bpf/test_cls_redirect_subprogs.bpf.o] Error 1
>
> The problem is the new offsetof() does not play nice with static asserts.
> Given that the context is a static assert (and CO-RE relocation is not
> needed at compile time), offsetof() usage can be replaced by restoring
> the original offsetof() definition as __builtin_offsetof().
>
> Fixes: bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")
> Reported-by: Colm Harrington <colm.harrington@oracle.com>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
>
> ---
> Changes since v1:
>
> - simplified to restore offsetof() definition in test_cls_redirect.h,
>    and added explanatory comment (Yonghong)
> ---
>   tools/testing/selftests/bpf/progs/test_cls_redirect.h | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/progs/test_cls_redirect.h b/tools/testing/selftests/bpf/progs/test_cls_redirect.h
> index 76eab0aacba0..233b089d1fba 100644
> --- a/tools/testing/selftests/bpf/progs/test_cls_redirect.h
> +++ b/tools/testing/selftests/bpf/progs/test_cls_redirect.h
> @@ -12,6 +12,15 @@
>   #include <linux/ipv6.h>
>   #include <linux/udp.h>
>   
> +/* offsetof() is used in static asserts, and the libbpf-redefined CO-RE
> + * friendly version breaks compilation for older clang versions <= 15
> + * when invoked in a static assert.  Restore original here.
> + */
> +#ifdef offsetof
> +#undef offsetof
> +#define offsetof(type, member) __builtin_offsetof(type, member)
> +#endif
> +

Oh, I just hit this too, and It's work for me.

Tested-by: Yipeng Zou <zouyipeng@huawei.com>

>   struct gre_base_hdr {
>   	uint16_t flags;
>   	uint16_t protocol;

-- 
Regards,
Yipeng Zou

Re: [PATCH v2 bpf] selftests/bpf: fix static assert compilation issue for test_cls_*.c

[Yonghong Song]

On 8/2/23 12:39 AM, Alan Maguire wrote:
> commit bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")
> 
> ...was backported to stable trees such as 5.15. The problem is that with older
> LLVM/clang (14/15) - which is often used for older kernels - we see compilation
> failures in BPF selftests now:
> 
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:90:2: error: static assertion expression is not an integral constant expression
>          sizeof(flow_ports_t) !=
>          ^~~~~~~~~~~~~~~~~~~~~~~
> progs/test_cls_redirect.c:91:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
>                  offsetofend(struct bpf_sock_tuple, ipv4.dport) -
>                  ^
> progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
>          (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
>           ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
>                                   ^
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:95:2: error: static assertion expression is not an integral constant expression
>          sizeof(flow_ports_t) !=
>          ^~~~~~~~~~~~~~~~~~~~~~~
> progs/test_cls_redirect.c:96:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
>                  offsetofend(struct bpf_sock_tuple, ipv6.dport) -
>                  ^
> progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
>          (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
>           ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
>                                   ^
> 2 errors generated.
> make: *** [Makefile:594: tools/testing/selftests/bpf/test_cls_redirect_subprogs.bpf.o] Error 1
> 
> The problem is the new offsetof() does not play nice with static asserts.
> Given that the context is a static assert (and CO-RE relocation is not
> needed at compile time), offsetof() usage can be replaced by restoring
> the original offsetof() definition as __builtin_offsetof().
> 
> Fixes: bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")
> Reported-by: Colm Harrington <colm.harrington@oracle.com>
> Signed-off-by: Alan Maguire <alan.maguire@oracle.com>

Acked-by: Yonghong Song <yonghong.song@linux.dev>

Re: [PATCH v2 bpf] selftests/bpf: fix static assert compilation issue for test_cls_*.c

[patchwork-bot+netdevbpf]

Hello:

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

On Wed,  2 Aug 2023 08:39:06 +0100 you wrote:
> commit bdeeed3498c7 ("libbpf: fix offsetof() and container_of() to work with CO-RE")
> 
> ...was backported to stable trees such as 5.15. The problem is that with older
> LLVM/clang (14/15) - which is often used for older kernels - we see compilation
> failures in BPF selftests now:
> 
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:90:2: error: static assertion expression is not an integral constant expression
>         sizeof(flow_ports_t) !=
>         ^~~~~~~~~~~~~~~~~~~~~~~
> progs/test_cls_redirect.c:91:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
>                 offsetofend(struct bpf_sock_tuple, ipv4.dport) -
>                 ^
> progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
>         (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
>          ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
>                                  ^
> In file included from progs/test_cls_redirect_subprogs.c:2:
> progs/test_cls_redirect.c:95:2: error: static assertion expression is not an integral constant expression
>         sizeof(flow_ports_t) !=
>         ^~~~~~~~~~~~~~~~~~~~~~~
> progs/test_cls_redirect.c:96:3: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression
>                 offsetofend(struct bpf_sock_tuple, ipv6.dport) -
>                 ^
> progs/test_cls_redirect.c:32:3: note: expanded from macro 'offsetofend'
>         (offsetof(TYPE, MEMBER) + sizeof((((TYPE *)0)->MEMBER)))
>          ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:86:33: note: expanded from macro 'offsetof'
>                                  ^
> 2 errors generated.
> make: *** [Makefile:594: tools/testing/selftests/bpf/test_cls_redirect_subprogs.bpf.o] Error 1
> 
> [...]

Here is the summary with links:
  - [v2,bpf] selftests/bpf: fix static assert compilation issue for test_cls_*.c
    https://git.kernel.org/bpf/bpf-next/c/416c6d01244e

You are awesome, thank you!
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