Small fixes to malloc debug.

- Change the printed name from pointer to allocation to be explicit about
  what is wrong.
- Change the signal to be SIGRTMAX - 19 instead of SIGRTMIN. This should
  prevent problems if we have to reserve other real time signals.

Bug: 28218530
Change-Id: Ic7d9c471929264d8e47bafaffc16e099840c9e71

libc/malloc_debug/Config.cpp

@@ -273,7 +273,7 @@ bool Config::SetFromProperties() {
   fill_free_value = DEFAULT_FILL_FREE_VALUE;
   front_guard_value = DEFAULT_FRONT_GUARD_VALUE;
   rear_guard_value = DEFAULT_REAR_GUARD_VALUE;
-  backtrace_signal = SIGRTMIN + 10;
+  backtrace_signal = SIGRTMAX - 19;
   free_track_backtrace_num_frames = 16;
 
   // Parse the options are of the format:

libc/malloc_debug/FreeTrackData.cpp

@@ -48,7 +48,7 @@ void FreeTrackData::LogFreeError(const Header* header, const uint8_t* pointer) {
   uint8_t fill_free_value = debug_->config().fill_free_value;
   for (size_t i = 0; i < header->usable_size; i++) {
     if (pointer[i] != fill_free_value) {
-      error_log("  pointer[%zu] = 0x%02x (expected 0x%02x)", i, pointer[i], fill_free_value);
+      error_log("  allocation[%zu] = 0x%02x (expected 0x%02x)", i, pointer[i], fill_free_value);
     }
   }
   auto back_iter = backtraces_.find(header);

libc/malloc_debug/GuardData.cpp

@@ -57,7 +57,7 @@ void GuardData::LogFailure(const Header* header, const void* pointer, const void
   const uint8_t* real = reinterpret_cast<const uint8_t*>(data);
   for (size_t i = 0; i < cmp_mem_.size(); i++, pointer_idx++) {
     if (real[i] != expected[i]) {
-      error_log("  pointer[%d] = 0x%02x (expected 0x%02x)", pointer_idx, real[i], expected[i]);
+      error_log("  allocation[%d] = 0x%02x (expected 0x%02x)", pointer_idx, real[i], expected[i]);
     }
   }