trace/kprobes: Allow return probes with offsets and absolute addresses

Since the kernel includes many non-global functions with same names, we
will need to use offsets from other symbols (typically _text/_stext) or
absolute addresses to place return probes on specific functions. Also,
the core register_kretprobe() API never forbid use of offsets or
absolute addresses with kretprobes.

Allow its use with the trace infrastructure. To distinguish kernels that
support this, update ftrace README to explicitly call this out.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/183e7ce2921a08c9c755ee9a5da3134febc6695b.1487770934.git.naveen.n.rao@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index f35109514a015c38de8b2e1da99399fd5f399692..0ed834d6beb0feeb68a35a88f048931923970bfe 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4355,6 +4355,7 @@ static const char readme_msg[] =
        "\t           -:[<group>/]<event>\n"
 #ifdef CONFIG_KPROBE_EVENTS
        "\t    place: [<module>:]<symbol>[+<offset>]|<memaddr>\n"
+  "place (kretprobe): [<module>:]<symbol>[+<offset>]|<memaddr>\n"
 #endif
 #ifdef CONFIG_UPROBE_EVENTS
        "\t    place: <path>:<offset>\n"

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index eadd96ef772f783b7e7d91a33db52522e7a53ade..18775ef182f85507b13cc06f3933bb9e803d9473 100644 (file)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -680,10 +680,6 @@ static int create_trace_kprobe(int argc, char **argv)
                return -EINVAL;
        }
        if (isdigit(argv[1][0])) {
-               if (is_return) {
-                       pr_info("Return probe point must be a symbol.\n");
-                       return -EINVAL;
-               }
                /* an address specified */
                ret = kstrtoul(&argv[1][0], 0, (unsigned long *)&addr);
                if (ret) {
@@ -699,10 +695,6 @@ static int create_trace_kprobe(int argc, char **argv)
                        pr_info("Failed to parse symbol.\n");
                        return ret;
                }
-               if (offset && is_return) {
-                       pr_info("Return probe must be used without offset.\n");
-                       return -EINVAL;
-               }
        }
        argc -= 2; argv += 2;