[RFC PATCH 4/6] perf bpf: Convert arglist to bpf prologue

[He Kuang]

When all arguments in bpf config section are collected in register and
offset form, this patch will fetch them from bpf context register and
place them as bpf input parameters.

Bpf prologue is generated as the following steps:
1. alloc dst address in stack -> r1
2. set size -> r2
3. fetch base register and offset -> r3
4. call BPF_FUNC_probe_read
5. loop 1
6. save intermediate result and process next arg
7. restore intermediate result to arg2~5

Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
---
 tools/perf/util/probe-event.c | 94 +++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/probe-event.h |  6 +++
 2 files changed, 100 insertions(+)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index d05b77c..c307cd7 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-loader.h"
 
 #define MAX_CMDLEN 256
 #define PERFPROBE_GROUP "probe"
@@ -1684,6 +1685,99 @@ static int synthesize_probe_trace_arg(struct probe_trace_arg *arg,
 	return buf - tmp;
 }
 
+#define BPF_STRBUF_ADD(buf, statement)		\
+	strbuf_add(buf,				\
+		&statement,			\
+		sizeof(struct bpf_insn))
+
+#define BPF_STRBUF_ADD_BUF(statement) BPF_STRBUF_ADD(buf, statement)
+
+int synthesize_probe_trace_arg_bpf_begin(struct strbuf *buf)
+{
+	/* save arg1 to ctx */
+	BPF_STRBUF_ADD_BUF(BPF_MOV64_REG(BPF_REG_CTX, BPF_REG_ARG1));
+	return 0;
+}
+
+int synthesize_probe_trace_arg_bpf_end(struct probe_trace_arg *arg,
+				struct strbuf *buf, int num)
+{
+	int i;
+
+	for (i = 0; i < num; i++) {
+		/* restore r7~10 to arg2~5*/
+		BPF_STRBUF_ADD_BUF(
+			BPF_MOV64_REG(BPF_REG_ARG2 + i, BPF_REG_7 + i));
+	}
+
+	/* assign result to tvar */
+	arg->insns = buf->buf;
+	arg->insns_cnt = (int)(buf->len/sizeof(struct bpf_insn));
+
+	return 0;
+}
+
+int synthesize_probe_trace_arg_bpf(struct probe_trace_arg *arg,
+				struct strbuf *buf, int index)
+{
+	struct probe_trace_arg_ref *ref = arg->ref;
+	int depth = 0;
+	int size = arg->reg_size;
+
+	if (size < 0)
+		return -EINVAL;
+
+	/* Special case: @XXX */
+	if (arg->value[0] == '@' && arg->ref)
+			ref = ref->next;
+
+	/* Print argument value */
+	if (arg->value[0] == '@' && arg->ref)
+		/* TODO parse other arguments */
+		pr_debug("%d%+ld", arg->regn,
+				 arg->ref->offset);
+	else {
+		/* load ctx to r3 */
+		BPF_STRBUF_ADD_BUF(
+			BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_CTX,
+				arg->regn * size));
+	}
+
+	/* parse and traslate to bpf bytecode */
+	while (ref) {
+		/* r3 offset */
+		BPF_STRBUF_ADD_BUF(
+			BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, ref->offset));
+
+		/* clear stack space */
+		BPF_STRBUF_ADD_BUF(BPF_ALU64_IMM(BPF_MOV, BPF_REG_1, 0));
+		BPF_STRBUF_ADD_BUF(
+			BPF_STX_MEM(BPF_DW, BPF_REG_FP, BPF_REG_1, -size));
+
+		/* set stack space to r1 */
+		BPF_STRBUF_ADD_BUF(BPF_MOV64_REG(BPF_REG_1, BPF_REG_FP));
+		BPF_STRBUF_ADD_BUF(BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -size));
+
+		/* r2 for size */
+		BPF_STRBUF_ADD_BUF(BPF_ALU64_IMM(BPF_MOV, BPF_REG_2, size));
+
+		/* call BPF_FUNC_probe_read */
+		BPF_STRBUF_ADD_BUF(BPF_EMIT_CALL(BPF_FUNC_probe_read));
+
+		/* result in stack, move to r3 */
+		BPF_STRBUF_ADD_BUF(
+			BPF_LDX_MEM(BPF_DW, BPF_REG_3, BPF_REG_FP, -size));
+
+		depth++;
+		ref = ref->next;
+	};
+
+	/* store intermediate results to r7~10 */
+	BPF_STRBUF_ADD_BUF(BPF_MOV64_REG(BPF_REG_7 + index, BPF_REG_3));
+
+	return 0;
+}
+
 char *synthesize_probe_trace_command(struct probe_trace_event *tev)
 {
 	struct probe_trace_point *tp = &tev->point;
diff --git a/tools/perf/util/probe-event.h b/tools/perf/util/probe-event.h
index 842d6c4..3b6c284 100644
--- a/tools/perf/util/probe-event.h
+++ b/tools/perf/util/probe-event.h
@@ -109,6 +109,12 @@ extern char *synthesize_perf_probe_command(struct perf_probe_event *pev);
 extern char *synthesize_probe_trace_command(struct probe_trace_event *tev);
 extern int synthesize_perf_probe_arg(struct perf_probe_arg *pa, char *buf,
 				     size_t len);
+/* generate bpf prologue from debuginfo */
+extern int synthesize_probe_trace_arg_bpf(struct probe_trace_arg *arg,
+					struct strbuf *buf, int index);
+extern int synthesize_probe_trace_arg_bpf_begin(struct strbuf *buf);
+extern int synthesize_probe_trace_arg_bpf_end(struct probe_trace_arg *arg,
+					struct strbuf *buf, int num);
 
 /* Check the perf_probe_event needs debuginfo */
 extern bool perf_probe_event_need_dwarf(struct perf_probe_event *pev);
-- 
1.8.5.2

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