[RFC PATCH v2 12/15] perf bpf: Generate bpf prologue without debuginfo

[He Kuang]

When probing at function entry, fallback to generate bpf prologue by
calling args if '$param' is the only args and no debuginfo is provided.

Signed-off-by: He Kuang <heku...@huawei.com>
---
 tools/perf/util/probe-event.c | 54 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index ccbf4d9..0de5879 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 <bpf/libbpf.h>
 #include <dwarf-regs.h>
 
 #define MAX_CMDLEN 256
@@ -287,6 +288,45 @@ static void clear_probe_trace_events(struct 
probe_trace_event *tevs, int ntevs)
                clear_probe_trace_event(tevs + i);
 }
 
+static int convert_parameters_to_bpf_prologue(char *new_prog, int *new_len)
+{
+       char *new_insn = new_prog;
+       int i;
+       int offset;
+
+       /* Find each argument */
+       for (i = 0; i < BPF_PROLOGUE_NRARGS_MAX; i++) {
+               offset = get_arch_calling_reg_offset(i);
+               if (offset < 0)
+                       break;
+
+               new_insn += bpf_prologue_formal_parameters(
+                       new_prog ? new_insn : NULL,
+                       offset, i);
+       }
+       *new_len = new_insn - new_prog;
+
+       return 0;
+}
+
+static int get_bpf_prologue_default(char **result, int *count)
+{
+       char *new_prog;
+
+       convert_parameters_to_bpf_prologue(NULL, count);
+       if (*count == 0)
+               return 0;
+
+       new_prog = malloc(*count);
+       if (!new_prog)
+               return -ENOMEM;
+
+       convert_parameters_to_bpf_prologue(new_prog, count);
+       *result = (char *)new_prog;
+
+       return 0;
+}
+
 static bool perf_probe_is_function_entry(struct perf_probe_event *pev)
 {
        if (pev->point.file || pev->point.line || pev->point.lazy_line)
@@ -931,7 +971,13 @@ int get_bpf_prologue(struct perf_probe_event *pev, char 
**result, int *count)
        if (!dinfo) {
                if (need_dwarf)
                        return -ENOENT;
-               pr_debug("Could not open debuginfo. Try to use symbols.\n");
+               pr_debug("Could not open debuginfo. Generate default 
prologue.\n");
+
+               if (perf_probe_is_function_entry(pev) &&
+                       pev->nargs == 1 &&
+                       !strcmp(pev->args[0].var, "$params"))
+                       return get_bpf_prologue_default(result, count);
+
                return 0;
        }
 
@@ -943,6 +989,12 @@ int get_bpf_prologue(struct perf_probe_event *pev, char 
**result, int *count)
 }
 #else  /* !HAVE_DWARF_SUPPORT */
 
+int get_bpf_prologue(struct perf_probe_event *pev __maybe_unused,
+               char **result, int *count)
+{
+       return -ENOTSUP;
+}
+
 static int
 find_perf_probe_point_from_dwarf(struct probe_trace_point *tp __maybe_unused,
                                 struct perf_probe_point *pp __maybe_unused,
-- 
1.8.5.2

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