[PATCH v4 13/18] perf clang jit: Allow jitted perf hook access BPF maps

[Wang Nan]

Newly introduced jit-helpers.[ch] defines a series of helpers which helps
jitted perf hook functions accessing BPF maps defined in their BPF scripts.
The helpers fetches fd of 'struct bpf_map' from 'struct bpf_object' and the
address of 'struct bpf_map_def' in jitted file. 'struct bpf_object' is the
context passed to hooks.

Jit helpers added in this commits are all leading with 'perf_'. We don't use
'bpf_' prefix because in following commits 'bpf_' prefix is going to be assigned
to kernel side BPF map operations. Same operation has different protocol for
kernel and user.

 Example:

  $ cat ./test.c
  /*******************************************************/
  #define SEC(name) __attribute__((section(name), used))
  #define BPF_MAP_TYPE_ARRAY 2
  #define BPF_MAP_TYPE_PERF_EVENT_ARRAY 4
  #define BPF_FUNC_map_lookup_elem 1
  static void *(*bpf_map_lookup_elem)(void *map, void *key) =
      (void *) BPF_FUNC_map_lookup_elem;
  struct bpf_map_def {
      unsigned int type;
      unsigned int key_size;
      unsigned int value_size;
      unsigned int max_entries;
  };
  struct bpf_map_def SEC("maps") counter = {
      .type = BPF_MAP_TYPE_ARRAY,
      .key_size = sizeof(int),
      .value_size = sizeof(int),
      .max_entries = 1,
  };
  extern int perf_map_update_elem(void *ctx, struct bpf_map_def *map,
                         void *key, void *value, unsigned long flags);
  extern int perf_map_lookup_elem(void *ctx, struct bpf_map_def *map,
                         void *key, void *value);
  SEC("sys_close=SyS_close")
  int sys_close(void *ctx)
  {
      int key = 0;
      int *value;
      value = bpf_map_lookup_elem(&counter, &key);
      if (!value)
          return 0;
      __sync_fetch_and_add(value, 1);
      return 0;
  }
  extern int printf(const char *fmt, ...);
  SEC("perfhook:record_start")
  void record_start(void *ctx)
  {
      int key = 0;
      int value = 100000000;
      printf("Welcom to perf record\n");
      perf_map_update_elem(ctx, &counter, &key, &value, 0);
  }

  SEC("perfhook:record_end")
  void record_end(void *ctx)
  {
      int key = 0;
      int value;
      perf_map_lookup_elem(ctx, &counter, &key, &value);
      printf("Goodbye, perf record, value=%d\n", value);
  }
  char _license[] SEC("license") = "GPL";
  int _version SEC("version") = LINUX_VERSION_CODE;
  /*******************************************************/
  $ sudo perf record  -e ./test.c echo Hehe
  Welcom to perf record
  Hehe
  [ perf record: Woken up 1 times to write data ]
  Goodbye, perf record, value=100000644
  [ perf record: Captured and wrote 0.014 MB perf.data ]

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Acked-by: Alexei Starovoitov <ast@xxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
---
 tools/perf/util/Build         |  1 +
 tools/perf/util/c++/clang.cpp |  9 ++++++-
 tools/perf/util/jit-helpers.c | 57 +++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/jit-helpers.h | 28 +++++++++++++++++++++
 4 files changed, 94 insertions(+), 1 deletion(-)
 create mode 100644 tools/perf/util/jit-helpers.c
 create mode 100644 tools/perf/util/jit-helpers.h

diff --git a/tools/perf/util/Build b/tools/perf/util/Build
index 3840e3a..e42ae4f 100644
--- a/tools/perf/util/Build
+++ b/tools/perf/util/Build
@@ -125,6 +125,7 @@ libperf-$(CONFIG_DWARF) += genelf_debug.o
 endif
 
 libperf-y += perf-hooks.o
+libperf-y += jit-helpers.o
 
 libperf-$(CONFIG_CXX) += c++/
 
diff --git a/tools/perf/util/c++/clang.cpp b/tools/perf/util/c++/clang.cpp
index 684855c..1bd92ea 100644
--- a/tools/perf/util/c++/clang.cpp
+++ b/tools/perf/util/c++/clang.cpp
@@ -38,6 +38,7 @@
 #include "llvm-utils.h"
 #include "util-cxx.h"
 #include "perf-hooks.h"
+#include "jit-helpers.h"
 
 namespace perf {
 
@@ -199,12 +200,18 @@ PerfModule::toBPFObject(void)
 	return std::move(Buffer);
 }
 
+#define __stringify_1(x)	#x
+#define __stringify(x)		__stringify_1(x)
 static std::map<const std::string, const void *> exported_funcs =
 {
-#define EXPORT(f) {#f, (const void *)&f}
+#define EXPORT(f) {__stringify(f), (const void *)&f}
 	EXPORT(test__clang_callback),
 	EXPORT(printf),
 	EXPORT(puts),
+	EXPORT(JIT_HELPER_FUNC_NAME(map_update_elem)),
+	EXPORT(JIT_HELPER_FUNC_NAME(map_lookup_elem)),
+	EXPORT(JIT_HELPER_FUNC_NAME(map_get_next_key)),
+	EXPORT(JIT_HELPER_FUNC_NAME(map_pin)),
 #undef EXPORT
 };
 
diff --git a/tools/perf/util/jit-helpers.c b/tools/perf/util/jit-helpers.c
new file mode 100644
index 0000000..1a37a20
--- /dev/null
+++ b/tools/perf/util/jit-helpers.c
@@ -0,0 +1,57 @@
+/*
+ * jit-helper.c
+ *
+ * Copyright (C) 2016 Wang Nan <wangnan0@xxxxxxxxxx>
+ * Copyright (C) 2016 Huawei Inc.
+ *
+ * Provide helpers which can be invoked by jit scripts attached to
+ * perf hooks.
+ */
+
+#include <util/jit-helpers.h>
+#include <util/bpf-loader.h>
+#include <bpf/libbpf.h>
+#include <bpf/bpf.h>
+
+#include "asm/bug.h"
+
+static int get_bpf_map_fd(struct bpf_object *obj, void *map)
+{
+	int fd;
+	char errbuf[BUFSIZ];
+
+	fd = bpf__map_fd(obj, map);
+	if (fd < 0) {
+		bpf__strerror_map_fd(obj, map, fd, errbuf, sizeof(errbuf));
+		WARN_ONCE(fd < 0, "Failed to get map fd: %s\n", errbuf);
+	}
+	return fd;
+}
+
+#define PARAMS(args...) args
+#define DEFINE_JIT_BPF_MAP_HELPER(name, proto, args)			\
+	JIT_BPF_MAP_HELPER(name, proto) {				\
+		int map_fd = get_bpf_map_fd(ctx, map);			\
+									\
+		if (map_fd < 0)						\
+			return map_fd;					\
+		return bpf_map_##name(map_fd, args);			\
+	}
+
+DEFINE_JIT_BPF_MAP_HELPER(update_elem,
+			  PARAMS(void *key, void *value, u64 flags),
+			  PARAMS(key, value, flags))
+
+DEFINE_JIT_BPF_MAP_HELPER(lookup_elem,
+			  PARAMS(void *key, void *value),
+			  PARAMS(key, value))
+
+DEFINE_JIT_BPF_MAP_HELPER(get_next_key,
+			  PARAMS(void *key, void *next_key),
+			  PARAMS(key, next_key))
+
+#define bpf_map_pin bpf_obj_pin
+DEFINE_JIT_BPF_MAP_HELPER(pin,
+			  PARAMS(const char *pathname),
+			  PARAMS(pathname));
+#undef bpf_map_pin
diff --git a/tools/perf/util/jit-helpers.h b/tools/perf/util/jit-helpers.h
new file mode 100644
index 0000000..b1f7479
--- /dev/null
+++ b/tools/perf/util/jit-helpers.h
@@ -0,0 +1,28 @@
+#ifndef JIT_HELPERS_H
+#define JIT_HELPERS_H
+
+#include <stdint.h>
+#include <util/perf-hooks.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define JIT_HELPER_FUNC_NAME(name) perf_##name
+
+#define JIT_HELPER(type, name, ...) \
+type JIT_HELPER_FUNC_NAME(name)(__VA_ARGS__)
+
+#define JIT_BPF_MAP_HELPER(name, ...) \
+	JIT_HELPER(int, map_##name, void *ctx, void *map, ##__VA_ARGS__)
+
+extern JIT_BPF_MAP_HELPER(update_elem, void *key, void *value, uint64_t flags);
+extern JIT_BPF_MAP_HELPER(lookup_elem, void *key, void *value);
+extern JIT_BPF_MAP_HELPER(get_next_key, void *key, void *next_key);
+extern JIT_BPF_MAP_HELPER(pin, const char *pathname);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
-- 
2.10.1