[sanitizer] Use runtime checks instead of API level for Android logging

Summary:
Recent Bionic have a slew of `async_safe_*` logging functions that are
basically the liblog ones but included within the libc. They have the advantage
of not allocating memory. `async_safe_write_log` does no formatting and is
likely the best candidate for logging.

Use a weak definition to try and use it. Also, avoid API level checks (as
the toolchain is compiled at a rather low API level) for `__android_log_write`
in favor of a weak definition as well.

Keep the fallback to `syslog` if nothing else was found.

I tried to overhaul the code block to only have a single #if SANITIZER_ANDROID
but I am not particularly attached to the form. LMKWYT.

Reviewers: eugenis

Reviewed By: eugenis

Subscribers: srhines, kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D40100

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@318410 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 38 insertions, 27 deletions

diff --git a/lib/sanitizer_common/sanitizer_linux_libcdep.cc b/lib/sanitizer_common/sanitizer_linux_libcdep.cc
index 0dc437585..3e64e90b5 100644
--- a/lib/sanitizer_common/sanitizer_linux_libcdep.cc
+++ b/lib/sanitizer_common/sanitizer_linux_libcdep.cc
@@ -48,10 +48,6 @@
 #include <android/api-level.h>
 #endif
 
-#if SANITIZER_ANDROID && __ANDROID_API__ < 21
-#include <android/log.h>
-#endif
-
 #if !SANITIZER_ANDROID
 #include <elf.h>
 #include <unistd.h>
@@ -538,12 +534,9 @@ uptr GetRSS() {
   return rss * GetPageSizeCached();
 }
 
-// 64-bit Android targets don't provide the deprecated __android_log_write.
-// Starting with the L release, syslog() works and is preferable to
-// __android_log_write.
 #if SANITIZER_LINUX
 
-#if SANITIZER_ANDROID
+# if SANITIZER_ANDROID
 static atomic_uint8_t android_log_initialized;
 
 void AndroidLogInit() {
@@ -554,35 +547,53 @@ void AndroidLogInit() {
 static bool ShouldLogAfterPrintf() {
   return atomic_load(&android_log_initialized, memory_order_acquire);
 }
-#else
-void AndroidLogInit() {}
 
-static bool ShouldLogAfterPrintf() { return true; }
-#endif  // SANITIZER_ANDROID
+extern "C" SANITIZER_WEAK_ATTRIBUTE
+int async_safe_write_log(int pri, const char* tag, const char* msg);
+extern "C" SANITIZER_WEAK_ATTRIBUTE
+int __android_log_write(int prio, const char* tag, const char* msg);
+
+// ANDROID_LOG_INFO is 4, but can't be resolved at runtime.
+#define SANITIZER_ANDROID_LOG_INFO 4
 
+// async_safe_write_log is basically __android_log_write but is only available
+// in recent versions of Bionic. __android_log_write was deprecated along the
+// way, so fallback to syslog if neither exists. The non-syslog alternatives
+// do not allocate memory and are preferable. Also syslog is broken pre-L, this
+// is another reason why we prefer __android_log_write if available.
 void WriteOneLineToSyslog(const char *s) {
-#if SANITIZER_ANDROID &&__ANDROID_API__ < 21
-  __android_log_write(ANDROID_LOG_INFO, NULL, s);
-#else
-  syslog(LOG_INFO, "%s", s);
-#endif
+  if (&async_safe_write_log) {
+    async_safe_write_log(SANITIZER_ANDROID_LOG_INFO, GetProcessName(), s);
+  } else if (&__android_log_write) {
+    __android_log_write(SANITIZER_ANDROID_LOG_INFO, nullptr, s);
+  } else {
+    syslog(LOG_INFO, "%s", s);
+  }
 }
 
-void LogMessageOnPrintf(const char *str) {
-  if (common_flags()->log_to_syslog && ShouldLogAfterPrintf())
-    WriteToSyslog(str);
-}
+extern "C" SANITIZER_WEAK_ATTRIBUTE
+void android_set_abort_message(const char *);
 
-#if SANITIZER_ANDROID
-extern "C" __attribute__((weak)) void android_set_abort_message(const char *);
 void SetAbortMessage(const char *str) {
-  if (&android_set_abort_message) android_set_abort_message(str);
+  if (&android_set_abort_message)
+    android_set_abort_message(str);
 }
-#else
+# else
+void AndroidLogInit() {}
+
+static bool ShouldLogAfterPrintf() { return true; }
+
+void WriteOneLineToSyslog(const char *s) { syslog(LOG_INFO, "%s", s); }
+
 void SetAbortMessage(const char *str) {}
-#endif
+# endif  // SANITIZER_ANDROID
+
+void LogMessageOnPrintf(const char *str) {
+  if (common_flags()->log_to_syslog && ShouldLogAfterPrintf())
+    WriteToSyslog(str);
+}
 
-#endif // SANITIZER_LINUX
+#endif  // SANITIZER_LINUX
 
 } // namespace __sanitizer