Implement __isOSVersionAtLeast for Android

[jiyong]

Summary

Add the implementation of __isOSVersionAtLeast for Android. Currently,
only the major version is checked against the API level of the platform
which is an integer. The API level is retrieved by reading the system
property ro.build.version.sdk (and optionally ro.build.version.codename
to see if the platform is released or not).

Patch by [e-mail]

Bug: 150860940
Bug: 134795810
Test: m

[jiyong]

Thanks Stephen. I now have the account here and ready to contribute. Let me fix the clang format errors.

[jiyong]

Re-formatted using clang-format

[jiyong]

Hi Reviewers,

This is a gentle ping asking for review.

[jiyong]

Handle the case when the system properties don't exist (e.g. on host)

[srhines]

Sorry, Jiyong, I had forgotten to subscribe llvm-commits when I first uploaded this (because it's part of compiler-rt and doesn't seem to have a default rule to add them). In any case, this patch LGTM, and I am going to go ahead and approve it since this only affects Android. Let's give it 24 hours for anyone else to comment before committing though (especially since I messed up with the original upload/review).

[jiyong]

No worries, and thanks for reviewing. I will wait for one another day.

[jiyong]

+24 hours has passed. Stephen, could you land this? (I don't think I have the privileged to do so, do I?)

[MaskRay]

Hi, git commits can set author and committer separately, please see https://llvm.org/docs/DeveloperPolicy.html#commit-messages https://llvm.org/docs/DeveloperPolicy.html#attribution-of-changes :)

Bug: 150860940
Bug: 134795810
Test: m

And this is not Gerrit. Such tags in the description can be distracting.

[smeenai]

compiler-rt/lib/builtins/os_version_check.c

232–234

This is inconsistent with android_get_device_api_level, which returns -1 on failure instead (per https://developer.android.com/ndk/reference/group/apilevels#android_get_device_api_level). How come a different behavior was chosen here? I don't know if it's at all likely for reading this property to fail anyway, but if it does, it seems confusing for an availability check to go in the opposite direction as a manual check based on android_get_device_api_level.

[jiyong]

compiler-rt/lib/builtins/os_version_check.c

232–234

How come a different behavior was chosen here?

The reasoning behind this code is that the exceptional case has to be resolved by this runtime library (in isOSVersionAtLeast), not by application, and isOSVersionAtLeast has no means of reporting an error; it returns boolean. So, when ro.build.version.sdk doesn't exist isOSVersionAtLeast can't help but return one of these three:

(1) return false regardless of Major

(2) return Major >= a_reasonably_old_api_level

(3) return true regardless of Major

We thought (1) is bad because it renders all APIs as unavailable, which probably doesn't reflect the reality. (2) is not good because people have different opinions on what a_reasonably_old_api_level should be. So we picked (3) as the least worst option.

The situation is different when users use android_get_device_api_level manually. If it returns -1, they can fallback to check the availability of the symbol manually by calling dlsym or similar.

---

Nevertheless, practically speaking, ro.build.version.sdk is guaranteed to exist. So this behavior won't be triggered anyway.

[smeenai]

compiler-rt/lib/builtins/os_version_check.c

232–234

That makes sense, thanks.

compiler-rt/lib/builtins/os_version_check.c

if (Major > GlobalMajor)
     return 0;
   if (Minor < GlobalMinor)
     return 1;
   if (Minor > GlobalMinor)
     return 0;
   return Subminor <= GlobalSubminor;
 }
 
+#elif __ANDROID__
+
+#include <pthread.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/system_properties.h>
+
+static int SdkVersion;
+static int IsPreRelease;
+
+static void readSystemProperties(void) {
+  char buf[PROP_VALUE_MAX];
+
+  if (__system_property_get("ro.build.version.sdk", buf) == 0) {
+    // When the system property doesn't exist, defaults to future API level.
+    SdkVersion = __ANDROID_API_FUTURE__;
+  } else {
+    SdkVersion = atoi(buf);
+  }
+
+  if (__system_property_get("ro.build.version.codename", buf) == 0) {
+    IsPreRelease = 1;
+  } else {
+    IsPreRelease = strcmp(buf, "REL") != 0;
+  }
+  return;
+}
+
+int32_t __isOSVersionAtLeast(int32_t Major, int32_t Minor, int32_t Subminor) {
+  (int32_t) Minor;
+  (int32_t) Subminor;
+  static pthread_once_t once = PTHREAD_ONCE_INIT;
+  pthread_once(&once, readSystemProperties);
+
+  return SdkVersion >= Major ||
+         (IsPreRelease && Major == __ANDROID_API_FUTURE__);
+}
+
 #else
 
 // Silence an empty translation unit warning.
 typedef int unused;
 
 #endif