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

Wang Nan
2015-04-30T10:53:40Z

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@huawei.com>
---
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