[PATCH bpf] libbpf: Fix undefined behavior in {get,put}_unaligned_be32()

[Eric Biggers <ebiggers@kernel.org>]

These violate aliasing rules and may be miscompiled unless
-fno-strict-aliasing is used.  Replace them with the standard memcpy()
solution.  Note that compilers know how to optimize this properly.

Fixes: 4a1c9e544b8d ("libbpf: remove linux/unaligned.h dependency for libbpf_sha256()")
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
---
 tools/lib/bpf/libbpf_utils.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/tools/lib/bpf/libbpf_utils.c b/tools/lib/bpf/libbpf_utils.c
index 5d66bc6ff0982..ac3beae54cf67 100644
--- a/tools/lib/bpf/libbpf_utils.c
+++ b/tools/lib/bpf/libbpf_utils.c
@@ -146,20 +146,24 @@ const char *libbpf_errstr(int err)
 		snprintf(buf, sizeof(buf), "%d", err);
 		return buf;
 	}
 }
 
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wpacked"
-#pragma GCC diagnostic ignored "-Wattributes"
-struct __packed_u32 { __u32 __val; } __attribute__((packed));
-#pragma GCC diagnostic pop
-
-#define get_unaligned_be32(p) be32_to_cpu((((struct __packed_u32 *)(p))->__val))
-#define put_unaligned_be32(v, p) do {							\
-	((struct __packed_u32 *)(p))->__val = cpu_to_be32(v);				\
-} while (0)
+static inline __u32 get_unaligned_be32(const void *p)
+{
+	__be32 val;
+
+	memcpy(&val, p, sizeof(val));
+	return be32_to_cpu(val);
+}
+
+static inline void put_unaligned_be32(__u32 val, void *p)
+{
+	__be32 be_val = cpu_to_be32(val);
+
+	memcpy(p, &be_val, sizeof(be_val));
+}
 
 #define SHA256_BLOCK_LENGTH 64
 #define Ch(x, y, z) (((x) & (y)) ^ (~(x) & (z)))
 #define Maj(x, y, z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
 #define Sigma_0(x) (ror32((x), 2) ^ ror32((x), 13) ^ ror32((x), 22))

base-commit: de7342228b7343774d6a9981c2ddbfb5e201044b
-- 
2.51.0