Add UMA for testing whether device supports memory mapping APK files with executable permissions.

base/android/linker/linker_jni.cc

Index: base/android/linker/linker_jni.cc
diff --git a/base/android/linker/linker_jni.cc b/base/android/linker/linker_jni.cc
index 79dd20103e7add06b2b30dd0550193682cbb7d50..83cc1ada24630ecf525a340bcc588722899ad4a1 100644
--- a/base/android/linker/linker_jni.cc
+++ b/base/android/linker/linker_jni.cc
@@ -15,7 +15,10 @@
 
 #include <android/log.h>
 #include <crazy_linker.h>
+#include <errno.h>
+#include <fcntl.h>
 #include <jni.h>
+#include <limits.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <unistd.h>
@@ -574,6 +577,44 @@ jlong GetRandomBaseLoadAddress(JNIEnv* env, jclass clazz, jlong bytes) {
   return static_cast<jlong>(reinterpret_cast<uintptr_t>(address));
 }
 
+// Check whether the device supports memory mapping APK files with executable
+// permissions.
+//
+// |env| is the current JNI environment handle and is ignored here.

[rmcilroy, 2014/10/10 16:26:08]

not ignored - used for string conversion

[petrcermak, 2014/10/10 17:13:24]

Done.

+// |clazz| is the static class handle for org.chromium.base.Linker,
+// and is ignored here.

[rmcilroy, 2014/10/10 16:26:08]

nit - I would just write "|class| is the static class handle which is not used
here."

[petrcermak, 2014/10/10 17:13:24]

Done.

+// |apkfile_name| is the filename of the APK.
+// Returns true if supported.
+jboolean CheckApkMemoryMappingSupport(JNIEnv* env, jclass clazz,
+                                      jstring apkfile_name) {
+  String apkfile_name_str(env, apkfile_name);
+  const char* apkfile_name_c_str = apkfile_name_str.c_str();
+
+  int fd = TEMP_FAILURE_RETRY(open(apkfile_name_c_str, O_RDONLY));

[rmcilroy, 2014/10/10 16:26:08]

I would avoid the TEMP_FAILURE_RETRY - it's not super critical that this
succeeds and I'm worried that we might end up in a retry loop here if glibc
decides it needs to keep retrying.

[petrcermak, 2014/10/10 17:13:24]

Done.

+  if (fd == -1) {
+    LOG_ERROR("%s: Failed to open %s\n", __FUNCTION__, apkfile_name_c_str);
+    return 0;
+  }
+
+  LOG_INFO("%s: Memory mapping the first page of %s\n", __FUNCTION__,
+           apkfile_name_c_str);
+  void* address = mmap(NULL, PAGE_SIZE, PROT_EXEC, MAP_PRIVATE, fd, 0);
+
+  jboolean success;
+  if (address == MAP_FAILED) {
+    success = 0;

[rmcilroy, 2014/10/10 16:26:08]

/s/0/false (and true for '1' below)

[petrcermak, 2014/10/10 17:13:24]

Done.

+  } else {
+    success = 1;
+    munmap(address, PAGE_SIZE);
+  }
+
+  TEMP_FAILURE_RETRY(close(fd));

[rmcilroy, 2014/10/10 16:26:08]

ditto

[petrcermak, 2014/10/10 17:13:24]

Done.

+
+  LOG_INFO("  %ssupported\n", success ? "" : "NOT ");
+  return success;
+
+}
+
 const JNINativeMethod kNativeMethods[] = {
     {"nativeLoadLibrary",
      "("
@@ -623,7 +664,13 @@ const JNINativeMethod kNativeMethods[] = {
      "J"
      ")"
      "J",
-     reinterpret_cast<void*>(&GetRandomBaseLoadAddress)}, };
+     reinterpret_cast<void*>(&GetRandomBaseLoadAddress)},
+     {"nativeCheckApkMemoryMappingSupport",
+      "("
+      "Ljava/lang/String;"
+      ")"
+      "Z",
+      reinterpret_cast<void*>(&CheckApkMemoryMappingSupport)}, };
 
 }  // namespace