tracing/probe: Add immediate parameter support

Add immediate value parameter (\1234) support to
probe events. This allows you to specify an immediate
(or dummy) parameter instead of fetching from memory
or register.

This feature looks odd, but imagine when you put a probe
on a code to trace some data. If the code is compiled into
2 instructions and 1 instruction has a value but other has
nothing since it is optimized out.
In that case, you can not fold those into one event, even
if ftrace supported multiple probes on one event.
With this feature, you can set a dummy value like
foo=\deadbeef instead of something like foo=%di.

Link: http://lkml.kernel.org/r/156095690733.28024.13258186548822649469.stgit@devnote2
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index fbb314b..5599305 100644 (file)
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -52,6 +52,7 @@ Synopsis of kprobe_events
   $retval      : Fetch return value.(\*2)
   $comm                : Fetch current task comm.
   +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*3)(\*4)
+  \IMM         : Store an immediate value to the argument.
   NAME=FETCHARG : Set NAME as the argument name of FETCHARG.
   FETCHARG:TYPE : Set TYPE as the type of FETCHARG. Currently, basic types
                  (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types

diff --git a/Documentation/trace/uprobetracer.rst b/Documentation/trace/uprobetracer.rst
index 6e75a6c..98cde99 100644 (file)
--- a/Documentation/trace/uprobetracer.rst
+++ b/Documentation/trace/uprobetracer.rst
@@ -45,6 +45,7 @@ Synopsis of uprobe_tracer
    $retval     : Fetch return value.(\*1)
    $comm       : Fetch current task comm.
    +|-[u]OFFS(FETCHARG) : Fetch memory at FETCHARG +|- OFFS address.(\*2)(\*3)
+   \IMM                : Store an immediate value to the argument.
    NAME=FETCHARG     : Set NAME as the argument name of FETCHARG.
    FETCHARG:TYPE     : Set TYPE as the type of FETCHARG. Currently, basic types
                       (u8/u16/u32/u64/s8/s16/s32/s64), hexadecimal types

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c7797a8..fb4003c 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4848,7 +4848,7 @@ static const char readme_msg[] =
 #else
        "\t           $stack<index>, $stack, $retval, $comm,\n"
 #endif
-       "\t           +|-[u]<offset>(<fetcharg>)\n"
+       "\t           +|-[u]<offset>(<fetcharg>), \\imm-value\n"
        "\t     type: s8/16/32/64, u8/16/32/64, x8/16/32/64, string, symbol,\n"
        "\t           b<bit-width>@<bit-offset>/<container-size>, ustring,\n"
        "\t           <type>\\[<array-size>\\]\n"

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index f8c3c65..fb90bae 100644 (file)
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -316,6 +316,17 @@ inval_var:
        return -EINVAL;
 }
 
+static int str_to_immediate(char *str, unsigned long *imm)
+{
+       if (isdigit(str[0]))
+               return kstrtoul(str, 0, imm);
+       else if (str[0] == '-')
+               return kstrtol(str, 0, (long *)imm);
+       else if (str[0] == '+')
+               return kstrtol(str + 1, 0, (long *)imm);
+       return -EINVAL;
+}
+
 /* Recursive argument parser */
 static int
 parse_probe_arg(char *arg, const struct fetch_type *type,
@@ -444,6 +455,13 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
                        code->offset = offset;
                }
                break;
+       case '\\':      /* Immediate value */
+               ret = str_to_immediate(arg + 1, &code->immediate);
+               if (ret)
+                       trace_probe_log_err(offs + 1, BAD_IMM);
+               else
+                       code->op = FETCH_OP_IMM;
+               break;
        }
        if (!ret && code->op == FETCH_OP_NOP) {
                /* Parsed, but do not find fetch method */

diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 2dcc4e3..cc113b8 100644 (file)
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -408,6 +408,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
        C(BAD_VAR,              "Invalid $-valiable specified"),        \
        C(BAD_REG_NAME,         "Invalid register name"),               \
        C(BAD_MEM_ADDR,         "Invalid memory address"),              \
+       C(BAD_IMM,              "Invalid immediate value"),             \
        C(FILE_ON_KPROBE,       "File offset is not available with kprobe"), \
        C(BAD_FILE_OFFS,        "Invalid file offset value"),           \
        C(SYM_ON_UPROBE,        "Symbol is not available with uprobe"), \