bpf: Add support to inline bpf_get_func_ip helper on x86

Adding support to inline it on x86, because it's single
load instruction.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220316122419.933957-6-jolsa@kernel.org

kernel/bpf/verifier.c

@@ -13678,7 +13678,7 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			continue;
 		}
 
-		/* Implement bpf_get_func_ip inline. */
+		/* Implement tracing bpf_get_func_ip inline. */
 		if (prog_type == BPF_PROG_TYPE_TRACING &&
 		    insn->imm == BPF_FUNC_get_func_ip) {
 			/* Load IP address from ctx - 16 */
@@ -13693,6 +13693,25 @@ static int do_misc_fixups(struct bpf_verifier_env *env)
 			continue;
 		}
 
+#ifdef CONFIG_X86
+		/* Implement kprobe_multi bpf_get_func_ip inline. */
+		if (prog_type == BPF_PROG_TYPE_KPROBE &&
+		    eatype == BPF_TRACE_KPROBE_MULTI &&
+		    insn->imm == BPF_FUNC_get_func_ip) {
+			/* Load IP address from ctx (struct pt_regs) ip */
+			insn_buf[0] = BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_1,
+						  offsetof(struct pt_regs, ip));
+
+			new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, 1);
+			if (!new_prog)
+				return -ENOMEM;
+
+			env->prog = prog = new_prog;
+			insn      = new_prog->insnsi + i + delta;
+			continue;
+		}
+#endif
+
 patch_call_imm:
 		fn = env->ops->get_func_proto(insn->imm, env->prog);
 		/* all functions that have prototype and verifier allowed

kernel/trace/bpf_trace.c

@@ -1039,6 +1039,7 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_kprobe = {
 
 BPF_CALL_1(bpf_get_func_ip_kprobe_multi, struct pt_regs *, regs)
 {
+	/* This helper call is inlined by verifier on x86. */
 	return instruction_pointer(regs);
 }