From: Andrii Nakryiko <andriin@fb.com>
Date: Tue, 15 Oct 2019 11:28:48 -0700
Subject: libbpf: Add BPF-side definitions of supported field relocation kinds
Patch-mainline: v5.5-rc1
Git-commit: 01340e31915bc73bf33a8f912ff1b74d514b8d79
References: bsc#1155518
Add enum definition for Clang's __builtin_preserve_field_info()
second argument (info_kind). Currently only byte offset and existence
are supported. Corresponding Clang changes introducing this built-in can
be found at [0]
[0] https://reviews.llvm.org/D67980
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20191015182849.3922287-5-andriin@fb.com
Acked-by: Gary Lin <glin@suse.com>
---
tools/lib/bpf/bpf_core_read.h | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
--- a/tools/lib/bpf/bpf_core_read.h
+++ b/tools/lib/bpf/bpf_core_read.h
@@ -3,6 +3,28 @@
#define __BPF_CORE_READ_H__
/*
+ * enum bpf_field_info_kind is passed as a second argument into
+ * __builtin_preserve_field_info() built-in to get a specific aspect of
+ * a field, captured as a first argument. __builtin_preserve_field_info(field,
+ * info_kind) returns __u32 integer and produces BTF field relocation, which
+ * is understood and processed by libbpf during BPF object loading. See
+ * selftests/bpf for examples.
+ */
+enum bpf_field_info_kind {
+ BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
+ BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
+};
+
+/*
+ * Convenience macro to check that field actually exists in target kernel's.
+ * Returns:
+ * 1, if matching field is present in target kernel;
+ * 0, if no matching field found.
+ */
+#define bpf_core_field_exists(field) \
+ __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
+
+/*
* 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.
@@ -12,7 +34,7 @@
* 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.
+ * semantics in comments to struct bpf_field_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