[PATCH net-next] selftests: bpf: modify urandom_read and link it non-statically

[Ivan Vecera]

After some experiences I found that urandom_read does not need to be
linked statically. When the 'read' syscall call is moved to separate
non-inlined function then bpf_get_stackid() is able to find
the executable in stack trace and extract its build_id from it.

Signed-off-by: Ivan Vecera <ivecera@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/Makefile       |  2 +-
 tools/testing/selftests/bpf/urandom_read.c | 15 +++++++++++----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 2aed37ea61a4..c33900a8fec0 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -69,7 +69,7 @@ TEST_CUSTOM_PROGS = $(OUTPUT)/urandom_read
 all: $(TEST_CUSTOM_PROGS)
 
 $(OUTPUT)/urandom_read: $(OUTPUT)/%: %.c
-	$(CC) -o $@ -static $< -Wl,--build-id
+	$(CC) -o $@ $< -Wl,--build-id
 
 BPFOBJ := $(OUTPUT)/libbpf.a
 
diff --git a/tools/testing/selftests/bpf/urandom_read.c b/tools/testing/selftests/bpf/urandom_read.c
index 9de8b7cb4e6d..db781052758d 100644
--- a/tools/testing/selftests/bpf/urandom_read.c
+++ b/tools/testing/selftests/bpf/urandom_read.c
@@ -7,11 +7,19 @@
 
 #define BUF_SIZE 256
 
+static __attribute__((noinline))
+void urandom_read(int fd, int count)
+{
+       char buf[BUF_SIZE];
+       int i;
+
+       for (i = 0; i < count; ++i)
+               read(fd, buf, BUF_SIZE);
+}
+
 int main(int argc, char *argv[])
 {
 	int fd = open("/dev/urandom", O_RDONLY);
-	int i;
-	char buf[BUF_SIZE];
 	int count = 4;
 
 	if (fd < 0)
@@ -20,8 +28,7 @@ int main(int argc, char *argv[])
 	if (argc == 2)
 		count = atoi(argv[1]);
 
-	for (i = 0; i < count; ++i)
-		read(fd, buf, BUF_SIZE);
+	urandom_read(fd, count);
 
 	close(fd);
 	return 0;
-- 
2.19.2