Merge branch 'libbpf: Add syscall-specific variant of BPF_KPROBE'

Hengqi Chen says:

====================

Add new macro BPF_KPROBE_SYSCALL, which provides easy access to syscall
input arguments. See [0] and [1] for background.

  [0]: https://github.com/libbpf/libbpf-bootstrap/issues/57
  [1]: https://github.com/libbpf/libbpf/issues/425

v2->v3:
  - Use PT_REGS_SYSCALL_REGS
  - Move selftest to progs/bpf_syscall_macro.c

v1->v2:
  - Use PT_REGS_PARM2_CORE_SYSCALL instead
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

tools/lib/bpf/bpf_tracing.h

@@ -470,4 +470,39 @@ typeof(name(0)) name(struct pt_regs *ctx)				    \
 }									    \
 static __always_inline typeof(name(0)) ____##name(struct pt_regs *ctx, ##args)
 
+#define ___bpf_syscall_args0()           ctx
+#define ___bpf_syscall_args1(x)          ___bpf_syscall_args0(), (void *)PT_REGS_PARM1_CORE_SYSCALL(regs)
+#define ___bpf_syscall_args2(x, args...) ___bpf_syscall_args1(args), (void *)PT_REGS_PARM2_CORE_SYSCALL(regs)
+#define ___bpf_syscall_args3(x, args...) ___bpf_syscall_args2(args), (void *)PT_REGS_PARM3_CORE_SYSCALL(regs)
+#define ___bpf_syscall_args4(x, args...) ___bpf_syscall_args3(args), (void *)PT_REGS_PARM4_CORE_SYSCALL(regs)
+#define ___bpf_syscall_args5(x, args...) ___bpf_syscall_args4(args), (void *)PT_REGS_PARM5_CORE_SYSCALL(regs)
+#define ___bpf_syscall_args(args...)     ___bpf_apply(___bpf_syscall_args, ___bpf_narg(args))(args)
+
+/*
+ * BPF_KPROBE_SYSCALL is a variant of BPF_KPROBE, which is intended for
+ * tracing syscall functions, like __x64_sys_close. It hides the underlying
+ * platform-specific low-level way of getting syscall input arguments from
+ * struct pt_regs, and provides a familiar typed and named function arguments
+ * syntax and semantics of accessing syscall input parameters.
+ *
+ * Original struct pt_regs* context is preserved as 'ctx' argument. This might
+ * be necessary when using BPF helpers like bpf_perf_event_output().
+ *
+ * This macro relies on BPF CO-RE support.
+ */
+#define BPF_KPROBE_SYSCALL(name, args...)				    \
+name(struct pt_regs *ctx);						    \
+static __attribute__((always_inline)) typeof(name(0))			    \
+____##name(struct pt_regs *ctx, ##args);				    \
+typeof(name(0)) name(struct pt_regs *ctx)				    \
+{									    \
+	struct pt_regs *regs = PT_REGS_SYSCALL_REGS(ctx);		    \
+	_Pragma("GCC diagnostic push")					    \
+	_Pragma("GCC diagnostic ignored \"-Wint-conversion\"")		    \
+	return ____##name(___bpf_syscall_args(args));			    \
+	_Pragma("GCC diagnostic pop")					    \
+}									    \
+static __attribute__((always_inline)) typeof(name(0))			    \
+____##name(struct pt_regs *ctx, ##args)
+
 #endif

tools/testing/selftests/bpf/prog_tests/test_bpf_syscall_macro.c

@@ -62,6 +62,12 @@ void test_bpf_syscall_macro(void)
 	ASSERT_EQ(skel->bss->arg4_core, exp_arg4, "syscall_arg4_core_variant");
 	ASSERT_EQ(skel->bss->arg5_core, exp_arg5, "syscall_arg5_core_variant");
 
+	ASSERT_EQ(skel->bss->option_syscall, exp_arg1, "BPF_KPROBE_SYSCALL_option");
+	ASSERT_EQ(skel->bss->arg2_syscall, exp_arg2, "BPF_KPROBE_SYSCALL_arg2");
+	ASSERT_EQ(skel->bss->arg3_syscall, exp_arg3, "BPF_KPROBE_SYSCALL_arg3");
+	ASSERT_EQ(skel->bss->arg4_syscall, exp_arg4, "BPF_KPROBE_SYSCALL_arg4");
+	ASSERT_EQ(skel->bss->arg5_syscall, exp_arg5, "BPF_KPROBE_SYSCALL_arg5");
+
 cleanup:
 	bpf_syscall_macro__destroy(skel);
 }

tools/testing/selftests/bpf/progs/bpf_syscall_macro.c

@@ -21,6 +21,12 @@ unsigned long arg4_core_cx = 0;
 unsigned long arg4_core = 0;
 unsigned long arg5_core = 0;
 
+int option_syscall = 0;
+unsigned long arg2_syscall = 0;
+unsigned long arg3_syscall = 0;
+unsigned long arg4_syscall = 0;
+unsigned long arg5_syscall = 0;
+
 const volatile pid_t filter_pid = 0;
 
 SEC("kprobe/" SYS_PREFIX "sys_prctl")
@@ -58,4 +64,21 @@ int BPF_KPROBE(handle_sys_prctl)
 	return 0;
 }
 
+SEC("kprobe/" SYS_PREFIX "sys_prctl")
+int BPF_KPROBE_SYSCALL(prctl_enter, int option, unsigned long arg2,
+		       unsigned long arg3, unsigned long arg4, unsigned long arg5)
+{
+	pid_t pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid != filter_pid)
+		return 0;
+
+	option_syscall = option;
+	arg2_syscall = arg2;
+	arg3_syscall = arg3;
+	arg4_syscall = arg4;
+	arg5_syscall = arg5;
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";