[RFC PATCH v2 09/15] perf probe: Support $params without debuginfo

[He Kuang <hekuang@huawei.com>]

When probing at function entry, fallback $params to calling regs if no
debuginfo is provided.

Before this path:
  $ perf probe -v --add='generic_perform_write $params'
  ...
  Added new event:
  Writing event: p:probe/generic_perform_write _stext+1246632 $params
  [86152.161204] Parse error at argument[0]. (-22)
  Failed to write event: Invalid argument
    Error: Failed to add events. Reason: Invalid argument (Code: -22)

After this patch:
  $ perf probe -v --add='generic_perform_write $params'
  ...
  Could not open debuginfo. Try to use symbols.
  ...
  Added new event:
  Writing event: p:probe/generic_perform_write _stext+1246632 %di %si %dx %cx %r8 %r9
    probe:generic_perform_write (on generic_perform_write with $params)

  You can now use it in all perf tools, such as:

    perf record -e probe:generic_perform_write -aR sleep 1

  $ perf record -e probe:generic_perform_write dd if=/dev/zero of=/mnt/data/test bs=4k count=3

  $ perf script
  dd  1149 [000] 18574.762652: probe:generic_perform_write: (ffffffff81130770) arg1=0xffff88007c37f600 arg2=0xffff88007ca87e70 arg3=0x0 arg4=0x0 arg5=0x556062e3 arg6=0x12a8010
  dd  1149 [000] 18574.762652: probe:generic_perform_write: (ffffffff81130770) arg1=0xffff88007c37f600 arg2=0xffff88007ca87e70 arg3=0x1000 arg4=0x0 arg5=0x556062e3 arg6=0x12a8010
  dd  1149 [000] 18574.762652: probe:generic_perform_write: (ffffffff81130770) arg1=0xffff88007c37f600 arg2=0xffff88007ca87e70 arg3=0x2000 arg4=0x0 arg5=0x556062e3 arg6=0x12a8010

Signed-off-by: He Kuang <hekuang@huawei.com>
---
 tools/perf/util/probe-event.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index d05b77c..7f9f431 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -46,6 +46,7 @@
 #include "probe-event.h"
 #include "probe-finder.h"
 #include "session.h"
+#include <dwarf-regs.h>
 
 #define MAX_CMDLEN 256
 #define PERFPROBE_GROUP "probe"
@@ -286,6 +287,14 @@ static void clear_probe_trace_events(struct probe_trace_event *tevs, int ntevs)
 		clear_probe_trace_event(tevs + i);
 }
 
+static bool perf_probe_is_function_entry(struct perf_probe_event *pev)
+{
+	if (pev->point.file || pev->point.line || pev->point.lazy_line)
+		return false;
+
+	return true;
+}
+
 #ifdef HAVE_DWARF_SUPPORT
 /*
  * Some binaries like glibc have special symbols which are on the symbol
@@ -1225,6 +1234,33 @@ static int parse_perf_probe_point(char *arg, struct perf_probe_event *pev)
 	return 0;
 }
 
+static char *parse_perf_probe_param(void)
+{
+	int i = 0;
+	struct strbuf sb;
+	bool first = true;
+	const char *reg_str;
+
+	strbuf_init(&sb, 16);
+
+	while (1) {
+		reg_str = get_arch_calling_reg_str(i++);
+		if (!reg_str)
+			break;
+
+		if (first) {
+			strbuf_addf(&sb, "%s", reg_str);
+			first = false;
+		} else
+			strbuf_addf(&sb, " %s", reg_str);
+	}
+
+	if (first)
+		strbuf_add(&sb, "", 1);
+
+	return strbuf_detach(&sb, NULL);
+}
+
 /* Parse perf-probe event argument */
 static int parse_perf_probe_arg(char *str, struct perf_probe_arg *arg)
 {
@@ -2543,6 +2579,12 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
 				goto nomem_out;
 		}
 		for (i = 0; i < tev->nargs; i++) {
+			if (perf_probe_is_function_entry(pev) &&
+				!strcmp(pev->args[i].var, "$params")) {
+				tev->args[i].value = parse_perf_probe_param();
+				continue;
+			}
+
 			if (pev->args[i].name)
 				tev->args[i].name =
 					strdup_or_goto(pev->args[i].name,
-- 
1.8.5.2