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Message-Id: <20221019083304.107157180@linuxfoundation.org>
Date: Wed, 19 Oct 2022 10:26:46 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
Toke Høiland-Jørgensen <toke@...e.dk>,
Andrii Nakryiko <andrii@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 6.0 319/862] libbpf: Dont require full struct enum64 in UAPI headers
From: Andrii Nakryiko <andrii@...nel.org>
[ Upstream commit 87dbdc230d162bf9ee1ac77c8ade178b6b1e199e ]
Drop the requirement for system-wide kernel UAPI headers to provide full
struct btf_enum64 definition. This is an unexpected requirement that
slipped in libbpf 1.0 and put unnecessary pressure ([0]) on users to have
a bleeding-edge kernel UAPI header from unreleased Linux 6.0.
To achieve this, we forward declare struct btf_enum64. But that's not
enough as there is btf_enum64_value() helper that expects to know the
layout of struct btf_enum64. So we get a bit creative with
reinterpreting memory layout as array of __u32 and accesing lo32/hi32
fields as array elements. Alternative way would be to have a local
pointer variable for anonymous struct with exactly the same layout as
struct btf_enum64, but that gets us into C++ compiler errors complaining
about invalid type casts. So play it safe, if ugly.
[0] Closes: https://github.com/libbpf/libbpf/issues/562
Fixes: d90ec262b35b ("libbpf: Add enum64 support for btf_dump")
Reported-by: Toke Høiland-Jørgensen <toke@...e.dk>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Toke Høiland-Jørgensen <toke@...e.dk>
Link: https://lore.kernel.org/bpf/20220927042940.147185-1-andrii@kernel.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
tools/lib/bpf/btf.h | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 583760df83b4..d421d656a076 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -487,6 +487,8 @@ static inline struct btf_enum *btf_enum(const struct btf_type *t)
return (struct btf_enum *)(t + 1);
}
+struct btf_enum64;
+
static inline struct btf_enum64 *btf_enum64(const struct btf_type *t)
{
return (struct btf_enum64 *)(t + 1);
@@ -494,7 +496,28 @@ static inline struct btf_enum64 *btf_enum64(const struct btf_type *t)
static inline __u64 btf_enum64_value(const struct btf_enum64 *e)
{
- return ((__u64)e->val_hi32 << 32) | e->val_lo32;
+ /* struct btf_enum64 is introduced in Linux 6.0, which is very
+ * bleeding-edge. Here we are avoiding relying on struct btf_enum64
+ * definition coming from kernel UAPI headers to support wider range
+ * of system-wide kernel headers.
+ *
+ * Given this header can be also included from C++ applications, that
+ * further restricts C tricks we can use (like using compatible
+ * anonymous struct). So just treat struct btf_enum64 as
+ * a three-element array of u32 and access second (lo32) and third
+ * (hi32) elements directly.
+ *
+ * For reference, here is a struct btf_enum64 definition:
+ *
+ * const struct btf_enum64 {
+ * __u32 name_off;
+ * __u32 val_lo32;
+ * __u32 val_hi32;
+ * };
+ */
+ const __u32 *e64 = (const __u32 *)e;
+
+ return ((__u64)e64[2] << 32) | e64[1];
}
static inline struct btf_member *btf_members(const struct btf_type *t)
--
2.35.1
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