[RFC PATCH v2 11/15] perf bpf: Synthesize vars to generate bpf prologue

[He Kuang]

After gethered all vars represented in trace_probe_arg, we can now use
functions in libbpf to generate the args prologue.

Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
---
 tools/perf/util/probe-finder.c | 83 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 81 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 6785eab..455ff0f 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1242,6 +1242,67 @@ end:
 	return ret;
 }
 
+/*
+ * Convert args to bpf prologue
+ * 1) First pass for calculating the new program length:
+ *   synthesize_probe_bpf(arg, nargs, NULL, &new_len);
+ *
+ * 2) 2nd pass do the actually convert
+ *   new_prog = malloc(sizeof(struct bpf_insn) * new_len);
+ *   synthesize_probe_bpf(arg, nargs, new_prog, &new_len);
+ */
+static int synthesize_probe_bpf(struct probe_trace_arg *arg,
+				int nargs,
+				char *new_prog,
+				int *new_len)
+{
+	int i;
+	char *new_insn = new_prog;
+
+	if (nargs == 0) {
+		*new_len = 0;
+		return 0;
+	}
+
+	new_insn += bpf_prologue_begin(new_prog);
+	/* Find each argument */
+	for (i = 0; i < nargs; i++) {
+		struct probe_trace_arg_ref *ref = arg[i].ref;
+		unsigned int regn = arg[i].regn;
+
+		/* Print argument value */
+		if (arg[i].value[0] == '@' && ref) {
+			/* TODO parse other arguments */
+			pr_debug("%d%+ld", regn, ref->offset);
+		} else {
+			int depth = 0;
+
+			new_insn += bpf_prologue_arg_deref(
+				get_arch_reg_offset(regn),
+				i + 1,
+				depth++,
+				new_prog ? new_insn : NULL,
+				!ref);
+
+			while (ref) {
+				new_insn += bpf_prologue_arg_deref(
+					ref->offset,
+					i + 1,
+					depth++,
+					new_prog ? new_insn : NULL,
+					!ref->next);
+				ref = ref->next;
+			}
+		}
+	}
+
+	new_insn += bpf_prologue_end(new_prog ? new_insn : NULL,
+					nargs);
+	*new_len = new_insn - new_prog;
+
+	return 0;
+}
+
 /* Add a found probe point into trace event list */
 static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
 {
@@ -1335,6 +1396,8 @@ int debuginfo__find_bpf_prologue(struct debuginfo *dbg,
 			.pf = {.pev = pev, .callback = generate_bpf_prologue},
 			.mod = dbg->mod, .max_tevs = BPF_MAX_TEVS};
 	struct probe_trace_event *tevs;
+	struct probe_trace_event *tev;
+	char *new_prog;
 	int ret;
 
 	/* Allocate result tevs array */
@@ -1347,9 +1410,25 @@ int debuginfo__find_bpf_prologue(struct debuginfo *dbg,
 
 	ret = debuginfo__find_probes(dbg, &tf.pf);
 
-	*result = NULL;
-	*count = 0;
+	tev = &tevs[0];
+
+	synthesize_probe_bpf(tev->args, tev->nargs, NULL, count);
+	if (*count == 0)
+		goto end;
+
+	new_prog = malloc(*count);
+	if (!new_prog) {
+		ret = -ENOMEM;
+		goto end;
+	}
 
+	synthesize_probe_bpf(tev->args, tev->nargs, new_prog, count);
+
+	/* assign result to tvar */
+	*result = (char *)new_prog;
+
+end:
+	/* release tevs */
 	free(tevs);
 	return ret;
 }
-- 
1.8.5.2

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