On Fri, 9 Dec 2016 15:19:38 +0100
Marcin Nowakowski <[email protected]> wrote:
> Commit 265a5b7ee3eb ("kprobes/trace: Fix kprobe selftest for gcc 4.6")
> has added __used attribute to kprobe_trace_selftest_target to ensure
> that the method is listed in kallsyms table.
>
> However, even though the method remains in the kernel image, the actual
> call is optimised away as there are no side efects and the return value
> is never checked.
Nice catch :)
>
> Add a return value check and a 'noinline' attribute to ensure that an
> inlined copy of the method is not used by the caller. Also add checks
> that verify that the kprobe was really hit, as at the moment the tests
> show positive results despite the test method being optimised away.
>
> Finally, add __init annotations to find_trace_probe_file() and
> kprobe_trace_selftest_target() as they are only called from within an
> __init method.
Right.
Looks good to me.
Acked-by: Masami Hiramatsu <[email protected]>
Thanks!
>
> Signed-off-by: Marcin Nowakowski <[email protected]>
> ---
> kernel/trace/trace_kprobe.c | 28 +++++++++++++++++++++++-----
> 1 file changed, 23 insertions(+), 5 deletions(-)
>
> v2: no changes
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index a2af1bc..a133ecd 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1361,18 +1361,18 @@ fs_initcall(init_kprobe_trace);
>
>
> #ifdef CONFIG_FTRACE_STARTUP_TEST
> -
> /*
> * The "__used" keeps gcc from removing the function symbol
> - * from the kallsyms table.
> + * from the kallsyms table. 'noinline' makes sure that there
> + * isn't an inlined version used by the test method below
> */
> -static __used int kprobe_trace_selftest_target(int a1, int a2, int a3,
> - int a4, int a5, int a6)
> +static __used __init noinline int
> +kprobe_trace_selftest_target(int a1, int a2, int a3, int a4, int a5, int a6)
> {
> return a1 + a2 + a3 + a4 + a5 + a6;
> }
>
> -static struct trace_event_file *
> +static struct __init trace_event_file *
> find_trace_probe_file(struct trace_kprobe *tk, struct trace_array *tr)
> {
> struct trace_event_file *file;
> @@ -1450,12 +1450,25 @@ static __init int kprobe_trace_self_tests_init(void)
>
> ret = target(1, 2, 3, 4, 5, 6);
>
> + /*
> + * Not expecting an error here, the check is only to prevent the
> + * optimizer from removing the call to target() as otherwise there
> + * are no side-effects and the call is never performed.
> + */
> + if (ret != 21)
> + warn++;
> +
> /* Disable trace points before removing it */
> tk = find_trace_kprobe("testprobe", KPROBE_EVENT_SYSTEM);
> if (WARN_ON_ONCE(tk == NULL)) {
> pr_warn("error on getting test probe.\n");
> warn++;
> } else {
> + if (trace_kprobe_nhit(tk) != 1) {
> + pr_warn("incorrect number of testprobe hits\n");
> + warn++;
> + }
> +
> file = find_trace_probe_file(tk, top_trace_array());
> if (WARN_ON_ONCE(file == NULL)) {
> pr_warn("error on getting probe file.\n");
> @@ -1469,6 +1482,11 @@ static __init int kprobe_trace_self_tests_init(void)
> pr_warn("error on getting 2nd test probe.\n");
> warn++;
> } else {
> + if (trace_kprobe_nhit(tk) != 1) {
> + pr_warn("incorrect number of testprobe2 hits\n");
> + warn++;
> + }
> +
> file = find_trace_probe_file(tk, top_trace_array());
> if (WARN_ON_ONCE(file == NULL)) {
> pr_warn("error on getting probe file.\n");
> --
> 2.7.4
>
--
Masami Hiramatsu <[email protected]>
