From: Andrii Nakryiko <andriin@fb.com>
To: <bpf@vger.kernel.org>, <netdev@vger.kernel.org>, <ast@fb.com>,
<daniel@iogearbox.net>, <yhs@fb.com>
Cc: <andrii.nakryiko@gmail.com>, <kernel-team@fb.com>,
Andrii Nakryiko <andriin@fb.com>
Subject: [PATCH v2 bpf-next 03/12] selftests/bpf: add BPF_CORE_READ relocatable read macro
Date: Tue, 30 Jul 2019 12:53:59 -0700 [thread overview]
Message-ID: <20190730195408.670063-4-andriin@fb.com> (raw)
In-Reply-To: <20190730195408.670063-1-andriin@fb.com>
Add BPF_CORE_READ macro used in tests to do bpf_core_read(), which
automatically captures offset relocation.
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
tools/testing/selftests/bpf/bpf_helpers.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index f804f210244e..81bc51293d11 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -501,4 +501,23 @@ struct pt_regs;
(void *)(PT_REGS_FP(ctx) + sizeof(ip))); })
#endif
+/*
+ * BPF_CORE_READ abstracts away bpf_probe_read() call and captures offset
+ * relocation for source address using __builtin_preserve_access_index()
+ * built-in, provided by Clang.
+ *
+ * __builtin_preserve_access_index() takes as an argument an expression of
+ * taking an address of a field within struct/union. It makes compiler emit
+ * a relocation, which records BTF type ID describing root struct/union and an
+ * accessor string which describes exact embedded field that was used to take
+ * an address. See detailed description of this relocation format and
+ * semantics in comments to struct bpf_offset_reloc in libbpf_internal.h.
+ *
+ * This relocation allows libbpf to adjust BPF instruction to use correct
+ * actual field offset, based on target kernel BTF type that matches original
+ * (local) BTF, used to record relocation.
+ */
+#define BPF_CORE_READ(dst, src) \
+ bpf_probe_read(dst, sizeof(*src), __builtin_preserve_access_index(src))
+
#endif
--
2.17.1
next prev parent reply other threads:[~2019-07-30 19:54 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-30 19:53 [PATCH v2 bpf-next 00/12] CO-RE offset relocations Andrii Nakryiko
2019-07-30 19:53 ` [PATCH v2 bpf-next 01/12] libbpf: add .BTF.ext offset relocation section loading Andrii Nakryiko
2019-07-30 21:19 ` Song Liu
2019-07-30 19:53 ` [PATCH v2 bpf-next 02/12] libbpf: implement BPF CO-RE offset relocation algorithm Andrii Nakryiko
2019-07-30 23:43 ` Song Liu
2019-07-30 23:55 ` Andrii Nakryiko
2019-07-31 0:16 ` Song Liu
2019-07-31 0:39 ` Song Liu
2019-07-31 1:00 ` Andrii Nakryiko
2019-07-31 5:19 ` Song Liu
2019-07-31 6:52 ` Andrii Nakryiko
2019-07-31 8:29 ` Song Liu
2019-07-31 17:18 ` Andrii Nakryiko
2019-07-31 17:46 ` Song Liu
2019-07-30 19:53 ` Andrii Nakryiko [this message]
2019-07-30 21:24 ` [PATCH v2 bpf-next 03/12] selftests/bpf: add BPF_CORE_READ relocatable read macro Song Liu
2019-07-30 21:26 ` Andrii Nakryiko
2019-07-30 21:33 ` Song Liu
2019-07-30 19:54 ` [PATCH v2 bpf-next 04/12] selftests/bpf: add CO-RE relocs testing setup Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 05/12] selftests/bpf: add CO-RE relocs struct flavors tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 06/12] selftests/bpf: add CO-RE relocs nesting tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 07/12] selftests/bpf: add CO-RE relocs array tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 08/12] selftests/bpf: add CO-RE relocs enum/ptr/func_proto tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 09/12] selftests/bpf: add CO-RE relocs modifiers/typedef tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 10/12] selftests/bpf: add CO-RE relocs ptr-as-array tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 11/12] selftests/bpf: add CO-RE relocs ints tests Andrii Nakryiko
2019-07-30 19:54 ` [PATCH v2 bpf-next 12/12] selftests/bpf: add CO-RE relocs misc tests Andrii Nakryiko
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