[RFC PATCH 06/22] perf bpf: check swap according to EHDR.

[Wang Nan]

Check endianess according to EHDR to support loading eBPF objects into
big endian machines. Code is taken from util/symbol-elf.c.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
---
 tools/perf/util/bpf-loader.c | 28 ++++++++++++++++++++++++++++
 tools/perf/util/bpf-loader.h |  1 +
 2 files changed, 29 insertions(+)

diff --git a/tools/perf/util/bpf-loader.c b/tools/perf/util/bpf-loader.c
index 3eb7504..14d76f6 100644
--- a/tools/perf/util/bpf-loader.c
+++ b/tools/perf/util/bpf-loader.c
@@ -76,6 +76,7 @@ static struct bpf_obj *bpf_obj_alloc(const char *path)
 	if (!obj)
 		goto out;
 
+	obj->needs_swap = false;
 	obj->elf.fd = -1;
 	return obj;
 out:
@@ -131,6 +132,31 @@ errout:
 	return err;
 }
 
+static int
+bpf_obj_swap_init(struct bpf_obj *obj)
+{
+	static unsigned int const endian = 1;
+
+	obj->needs_swap = false;
+
+	switch (obj->elf.ehdr.e_ident[EI_DATA]) {
+	case ELFDATA2LSB:
+		/* We are big endian, BPF obj is little endian. */
+		if (*(unsigned char const *)&endian != 1)
+			obj->needs_swap = true;
+		return 0;
+
+	case ELFDATA2MSB:
+		/* We are little endian, BPF obj is big endian. */
+		if (*(unsigned char const *)&endian != 0)
+			obj->needs_swap = true;
+		return 0;
+
+	default:
+		return -EINVAL;
+	}
+}
+
 int bpf__load(const char *path)
 {
 	struct bpf_obj *obj;
@@ -151,6 +177,8 @@ int bpf__load(const char *path)
 
 	if ((err = bpf_obj_elf_init(obj)))
 		goto out;
+	if ((err = bpf_obj_swap_init(obj)))
+		goto out;
 
 	list_add(&obj->list, &bpf_obj_list);
 	return 0;
diff --git a/tools/perf/util/bpf-loader.h b/tools/perf/util/bpf-loader.h
index 6a6651b..c27b0ac 100644
--- a/tools/perf/util/bpf-loader.h
+++ b/tools/perf/util/bpf-loader.h
@@ -22,6 +22,7 @@ struct bpf_obj {
 	/* All bpf objs should be linked together. */
 	struct list_head list;
 	char *path;
+	bool needs_swap;
 
 	/*
 	 * Information when doing elf related work. Only valid if fd
-- 
1.8.3.4

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