[RFC PATCH v2 08/15] bpf tools: Fetch calling regs to bpf arglist

[He Kuang]

For generating bpf prologue which fetches function formal parameters
when debuginfo is not provided.

Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
---
 tools/lib/bpf/gen_prologue.c | 19 +++++++++++++++++++
 tools/lib/bpf/libbpf.h       |  2 ++
 2 files changed, 21 insertions(+)

diff --git a/tools/lib/bpf/gen_prologue.c b/tools/lib/bpf/gen_prologue.c
index ca8aa1c..d25693a 100644
--- a/tools/lib/bpf/gen_prologue.c
+++ b/tools/lib/bpf/gen_prologue.c
@@ -106,3 +106,22 @@ unsigned int bpf_prologue_end(char *new_prog, int nargs)
 
 	return (char *)new_insn - new_prog;
 }
+
+unsigned int bpf_prologue_formal_parameters(char *new_prog, int offset,
+					int index)
+{
+	struct bpf_insn *new_insn;
+
+	if (index >= BPF_PROLOGUE_NRARGS_MAX)
+		return 0;
+
+	new_insn = (struct bpf_insn *)new_prog;
+
+	/* load ctx to r3 */
+	if (new_prog)
+		*new_insn = BPF_LDX_MEM(BPF_DW, BPF_REG_ARG2 + index,
+				BPF_REG_ARG1, offset);
+	new_insn++;
+
+	return (char *)new_insn - new_prog;
+}
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index cf22a6a..9d6d4f7 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -72,5 +72,7 @@ unsigned int bpf_prologue_arg_deref(int offset,
 				int depth,
 				char *new_prog,
 				bool last);
+unsigned int bpf_prologue_formal_parameters(char *new_prog, int offset,
+					int index);
 
 #endif
-- 
1.8.5.2

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