Add logging/selective build support

mace/BUILD

+config_setting(
+    name = "android",
+    values = {
+        "crosstool_top": "//external:android/crosstool",
+    },
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
+    name = "android_armv7",
+    values = {
+        "crosstool_top": "//external:android/crosstool",
+        "android_cpu": "armeabi-v7a",
+    },
+    visibility = ["//visibility:public"],
+)
+
+config_setting(
+    name = "android_arm64",
+    values = {
+        "crosstool_top": "//external:android/crosstool",
+        "android_cpu": "arm64-v8a",
+    },
+    visibility = ["//visibility:public"],
+)

mace/core/BUILD

+package(default_visibility = ["//visibility:public"])
+
+cc_library(
+    name = "lib_core",
+    hdrs = [
+        "logging.h"
+        ],
+    srcs = [
+        ],
+    )

mace/core/logging.h

+#ifndef MACE_COMMON_LOGGING_H_
+#define MACE_COMMON_LOGGING_H_
+
+#ifdef __ANDROID__
+#include <android/log.h>
+#else
+#include <cstdio>
+#endif
+
+namespace mace {
+
+const int FATAL = 0;
+const int ERROR = 1;
+const int WARN = 2;
+const int INFO = 3;
+const int DEBUG = 4;
+const int VERBOSE = 5;
+
+namespace internal {
+
+const char *kTag = "MACE";
+
+
+#ifdef __ANDROID__
+
+#define _MACE_LOG_FATAL \
+  do { \
+    __android_log_print(ANDROID_LOG_FATAL, mace::internal::kTag, __VA_ARGS__); \
+    abort(); \
+  } while (0)
+
+#define _MACE_LOG_ERROR(...) \
+  __android_log_print(ANDROID_LOG_ERROR, mace::internal::kTag, __VA_ARGS__)
+#define _MACE_LOG_WARN(...) \
+  __android_log_print(ANDROID_LOG_WARN, mace::internal::kTag, __VA_ARGS__)
+#define _MACE_LOG_INFO(...) \
+  __android_log_print(ANDROID_LOG_INFO, mace::internal::kTag, __VA_ARGS__)
+#define _MACE_LOG_DEBUG(...) \
+  __android_log_print(ANDROID_LOG_DEBUG, mace::internal::kTag, __VA_ARGS__)
+#define _MACE_LOG_VERBOSE(...) \
+  __android_log_print(ANDROID_LOG_VERBOSE, mace::internal::kTag, __VA_ARGS__)
+  
+
+#define LOG(severity, ...) _MACE_LOG_##severity(__VA_ARGS__)
+
+#else // Non Android, just for tests
+
+// TODO(heliangliang): Fix newline
+#define LOG(severity, ...) \
+  do { \
+    printf(__VA_ARGS__); \
+    printf("\n"); \
+  } while (0)
+
+#endif // __ANDROID__
+
+} // namespace internal
+} // namespace mace
+
+#endif // MACE_COMMON_LOGGING_H_

mace/examples/BUILD

 # Examples
+load(
+    "//mace:mace.bzl",
+    "if_android",
+    )
 
 cc_binary(
     name = "helloworld",
     srcs = [
         "helloworld.cc",
         ],
-    linkopts = [
-        "-pie",
-        ]
+    deps = [
+        "//mace/core:lib_core",
+        ],
+    linkopts = if_android(["-pie", "-llog"])
     )

mace/examples/README.md

 Examples
 =======
 
-* Build the example
+* Build the example (e.g., with armeabi-v7a target)
 ```
 bazel build mace/examples:helloworld \
    --crosstool_top=//external:android/crosstool \
@@ -9,7 +9,7 @@ bazel build mace/examples:helloworld \
    --cpu=armeabi-v7a
 ```
 
-* To run adb inside docker, the network should use 'host':
+* To run adb inside docker, the container network should use 'host'
 ```
 docker run -it --net=host mace-dev /bin/bash
 ```
@@ -20,3 +20,8 @@ adb shell "mkdir /data/local/tmp/helloword"
 adb shell push bazel-bin/mace/examples/helloworld /data/local/tmp/helloword
 adb shell /data/local/tmp/helloword/helloworld
 ```
+
+* Check the logs
+```
+adb logcat | grep MACE
+```

mace/examples/helloworld.cc

-#include <cstdio>
+#include "mace/core/logging.h"
 
 int main() {
-  printf("Hello world\n");
+  LOG(INFO, "Hello World");
+
   return 0;
 }

mace/mace.bzl

+# -*- Python -*-
+
+def if_android(a):
+  return select({
+      "//mace:android": a,
+      "//conditions:default": [],
+  })
+
+def if_not_android(a):
+  return select({
+      "//mace:android": [],
+      "//conditions:default": a,
+  })
+
+def if_android_armv7(a):
+  return select({
+      "//mace:android_armv7": a,
+      "//conditions:default": [],
+  })
+
+def if_android_arm64(a):
+  return select({
+      "//mace:android_arm64": a,
+      "//conditions:default": [],
+  })