netdev - [PATCH v2 bpf-next 3/9] libbpf: simplify endianness check

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Date:   Wed, 29 May 2019 10:36:05 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <andrii.nakryiko@...il.com>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>,
        <kernel-team@...com>
CC:     Andrii Nakryiko <andriin@...com>
Subject: [PATCH v2 bpf-next 3/9] libbpf: simplify endianness check

Rewrite endianness check to use "more canonical" way, using
compiler-defined macros, similar to few other places in libbpf. It also
is more obvious and shorter.

Acked-by: Song Liu <songliubraving@...com>
Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/lib/bpf/libbpf.c | 37 ++++++++++++-------------------------
 1 file changed, 12 insertions(+), 25 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 5af331cb8e4f..fe700ef1135d 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -607,31 +607,18 @@ static int bpf_object__elf_init(struct bpf_object *obj)
 	return err;
 }
 
-static int
-bpf_object__check_endianness(struct bpf_object *obj)
-{
-	static unsigned int const endian = 1;
-
-	switch (obj->efile.ehdr.e_ident[EI_DATA]) {
-	case ELFDATA2LSB:
-		/* We are big endian, BPF obj is little endian. */
-		if (*(unsigned char const *)&endian != 1)
-			goto mismatch;
-		break;
-
-	case ELFDATA2MSB:
-		/* We are little endian, BPF obj is big endian. */
-		if (*(unsigned char const *)&endian != 0)
-			goto mismatch;
-		break;
-	default:
-		return -LIBBPF_ERRNO__ENDIAN;
-	}
-
-	return 0;
-
-mismatch:
-	pr_warning("Error: endianness mismatch.\n");
+static int bpf_object__check_endianness(struct bpf_object *obj)
+{
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+	if (obj->efile.ehdr.e_ident[EI_DATA] == ELFDATA2LSB)
+		return 0;
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	if (obj->efile.ehdr.e_ident[EI_DATA] == ELFDATA2MSB)
+		return 0;
+#else
+# error "Unrecognized __BYTE_ORDER__"
+#endif
+	pr_warning("endianness mismatch.\n");
 	return -LIBBPF_ERRNO__ENDIAN;
 }
 
-- 
2.17.1