Add Android standalone log target (#6590)

Summary:

Add a standalone Android log target to enable ExecuTorch logging to logcat when not using JNI bindings.

Differential Revision: D65268257

Author: GregoryComer

extension/android/BUCK

@@ -1,4 +1,5 @@
 load("@fbsource//tools/build_defs/android:fb_android_library.bzl", "fb_android_library")
+load("@fbsource//tools/build_defs:fb_xplat_cxx_library.bzl", "fb_xplat_cxx_library")
 
 oncall("executorch")
 
@@ -39,3 +40,17 @@ fb_android_library(
         "//fbandroid/libraries/soloader/java/com/facebook/soloader/nativeloader:nativeloader",
     ],
 )
+
+fb_xplat_cxx_library(
+    name = "log_provider",
+    srcs = ["jni/log.cpp"],
+    compiler_flags = [
+        "-frtti",
+        "-fexceptions",
+        "-Wno-unused-variable",
+    ],
+    deps = [
+        "//xplat/executorch/runtime/platform:platform",
+    ],
+    visibility = ["PUBLIC"],
+)

extension/android/jni/BUCK

@@ -25,7 +25,7 @@ executorch_generated_lib(
 
 fb_android_cxx_library(
     name = "executorch_jni",
-    srcs = ["jni_layer.cpp"],
+    srcs = ["jni_layer.cpp", "log.cpp"],
     headers = ["jni_layer_constants.h"],
     allow_jni_merging = False,
     compiler_flags = [
@@ -49,7 +49,7 @@ fb_android_cxx_library(
 
 fb_android_cxx_library(
     name = "executorch_jni_full",
-    srcs = ["jni_layer.cpp"],
+    srcs = ["jni_layer.cpp", "log.cpp"],
     headers = ["jni_layer_constants.h"],
     allow_jni_merging = False,
     compiler_flags = [

extension/android/jni/jni_layer.cpp

@@ -33,33 +33,6 @@
 #include <fbjni/ByteBuffer.h>
 #include <fbjni/fbjni.h>
 
-#ifdef __ANDROID__
-#include <android/log.h>
-
-// For Android, write to logcat
-void et_pal_emit_log_message(
-    et_timestamp_t timestamp,
-    et_pal_log_level_t level,
-    const char* filename,
-    const char* function,
-    size_t line,
-    const char* message,
-    size_t length) {
-  int android_log_level = ANDROID_LOG_UNKNOWN;
-  if (level == 'D') {
-    android_log_level = ANDROID_LOG_DEBUG;
-  } else if (level == 'I') {
-    android_log_level = ANDROID_LOG_INFO;
-  } else if (level == 'E') {
-    android_log_level = ANDROID_LOG_ERROR;
-  } else if (level == 'F') {
-    android_log_level = ANDROID_LOG_FATAL;
-  }
-
-  __android_log_print(android_log_level, "ExecuTorch", "%s", message);
-}
-#endif
-
 using namespace executorch::extension;
 using namespace torch::executor;
 

extension/android/jni/log.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <executorch/runtime/platform/log.h>
+#include <executorch/runtime/platform/platform.h>
+#include <executorch/runtime/platform/runtime.h>
+
+#ifdef __ANDROID__
+#include <android/log.h>
+
+// For Android, write to logcat
+void et_pal_emit_log_message(
+    et_timestamp_t timestamp,
+    et_pal_log_level_t level,
+    const char* filename,
+    const char* function,
+    size_t line,
+    const char* message,
+    size_t length) {
+  int android_log_level = ANDROID_LOG_UNKNOWN;
+  if (level == 'D') {
+    android_log_level = ANDROID_LOG_DEBUG;
+  } else if (level == 'I') {
+    android_log_level = ANDROID_LOG_INFO;
+  } else if (level == 'E') {
+    android_log_level = ANDROID_LOG_ERROR;
+  } else if (level == 'F') {
+    android_log_level = ANDROID_LOG_FATAL;
+  }
+
+  __android_log_print(android_log_level, "ExecuTorch", "%s", message);
+}
+#endif