Re: [PATCH bpf-next] selftests/bpf: Fix test_attach_probe for powerpc uprobes

On Mon, Mar 01, 2021 at 02:58:53PM -0800, Yonghong Song wrote:

On 3/1/21 11:04 AM, Jiri Olsa wrote:

quoted

When testing uprobes we the test gets GEP (Global Entry Point)
address from kallsyms, but then the function is called locally
so the uprobe is not triggered.

Fixing this by adjusting the address to LEP (Local Entry Point)
for powerpc arch.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
  .../selftests/bpf/prog_tests/attach_probe.c    | 18 +++++++++++++++++-
  1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index a0ee87c8e1ea..c3cfb48d3ed0 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c

@@ -2,6 +2,22 @@
  #include <test_progs.h>
  #include "test_attach_probe.skel.h"
+#if defined(__powerpc64__)
+/*
+ * We get the GEP (Global Entry Point) address from kallsyms,
+ * but then the function is called locally, so we need to adjust
+ * the address to get LEP (Local Entry Point).

Any documentation in the kernel about this behavior? This will
help to validate the change without trying with powerpc64 qemu...

we got similar fix in perf:

7b6ff0bdbf4f perf probe ppc64le: Fixup function entry if using kallsyms lookup

CC-ing few other folks from ppc land for more info

jirka

quoted

+ */
+#define LEP_OFFSET 8
+
+static ssize_t get_offset(ssize_t offset)
+{
+	return offset + LEP_OFFSET;
+}
+#else
+#define get_offset(offset) (offset)
+#endif
+
  ssize_t get_base_addr() {
  	size_t start, offset;
  	char buf[256];

@@ -36,7 +52,7 @@ void test_attach_probe(void)
  	if (CHECK(base_addr < 0, "get_base_addr",
  		  "failed to find base addr: %zd", base_addr))
  		return;
-	uprobe_offset = (size_t)&get_base_addr - base_addr;
+	uprobe_offset = get_offset((size_t)&get_base_addr - base_addr);
  	skel = test_attach_probe__open_and_load();
  	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))