done in v3. Thanks!

On Mon, Jan 25, 2021 at 9:37 PM Andrii Nakryiko
[off-list ref] wrote:

On Sun, Jan 24, 2021 at 11:54 AM Andrei Matei [off-list ref] wrote:

quoted

Add a higher-level test (C BPF program) for the new functionality -
variable access stack reads and writes.

Signed-off-by: Andrei Matei <redacted>
---
 .../selftests/bpf/prog_tests/stack_var_off.c  | 56 +++++++++++++++++++
 .../selftests/bpf/progs/test_stack_var_off.c  | 43 ++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/stack_var_off.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_stack_var_off.c

diff --git a/tools/testing/selftests/bpf/prog_tests/stack_var_off.c b/tools/testing/selftests/bpf/prog_tests/stack_var_off.c
new file mode 100644
index 000000000000..c4c47fb0f0af
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/stack_var_off.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <test_progs.h>
+#include "test_stack_var_off.skel.h"
+
+int dummy;
+
+noinline void uprobed_function(char *s, int len)
+{
+       /* Do something to keep the compiler from removing the function.
+        */
+       dummy++;
+}
+
+void test_stack_var_off(void)
+{
+       int duration = 0;
+       struct bpf_link *uprobe_link;
+       struct test_stack_var_off *skel;
+       size_t uprobe_offset;
+       ssize_t base_addr;
+       char s[100];
+
+       base_addr = get_base_addr();
+       if (CHECK(base_addr < 0, "get_base_addr",
+                 "failed to find base addr: %zd", base_addr))
+               return;
+       uprobe_offset = (size_t)&uprobed_function - base_addr;
+
+       skel = test_stack_var_off__open_and_load();
+       if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+               return;
+       if (CHECK(!skel->bss, "check_bss", ".bss wasn't mmap()-ed\n"))
+               goto cleanup;
+
+       uprobe_link = bpf_program__attach_uprobe(skel->progs.uprobe,
+                                                false /* retprobe */,
+                                                0 /* self pid */,
+                                                "/proc/self/exe",
+                                                uprobe_offset);
+       if (CHECK(IS_ERR(uprobe_link), "attach_uprobe",
+                 "err %ld\n", PTR_ERR(uprobe_link)))
+               goto cleanup;
+       skel->links.uprobe = uprobe_link;
+
+       /* trigger uprobe */
+       s[0] = 1;
+       s[1] = 10;
+       uprobed_function(&s[0], 2);

I don't think uprobe() is essential to this test and just obscured
what is being tested. I'd just use a global variable to pass whatever
input data you need and use usleep(1), just like lots of other tests.

quoted

+
+       if (CHECK(skel->bss->uprobe_res != 10, "check_uprobe_res",
+                 "wrong uprobe res: %d\n", skel->bss->uprobe_res))
+               goto cleanup;
+
+cleanup:
+       test_stack_var_off__destroy(skel);
+}

diff --git a/tools/testing/selftests/bpf/progs/test_stack_var_off.c b/tools/testing/selftests/bpf/progs/test_stack_var_off.c
new file mode 100644
index 000000000000..44f982684541
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_stack_var_off.c

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2017 Facebook
+
+#include <linux/ptrace.h>
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+int uprobe_res;
+
+SEC("uprobe/func")
+int BPF_KPROBE(uprobe, char *s, int len)
+{
+       /* This BPF program performs variable-offset reads and writes on a
+        * stack-allocated buffer.
+        */
+       char buf[16];
+       unsigned long idx;
+       char out;
+
+       /* Zero-out the buffer so we can read anywhere inside it. */
+       __builtin_memset(&buf, 0, 16);
+       /* Copy the contents of s from user-space. */
+       len &= 0xf;
+       if (bpf_probe_read_user(&buf, len, s)) {
+               bpf_printk("error reading user mem\n");
+               return 1;
+       }
+       /* Index into the buffer at an unknown offset that comes from the
+        * buffer itself. This is a variable-offset stack read.
+        */
+       idx = buf[0];
+       idx &= 0xf;
+       out = buf[idx];
+       /* Append something to the buffer. The position where we append it
+        * is unknown. This is a variable-offset stack write.
+        */
+       buf[len] = buf[idx];
+       uprobe_res = out;
+       return 0;
+}
+
+char _license[] SEC("license") = "GPL";
--

2.27.0