Change the way some maps are printed.

Before, an anonymous map wound up printing the pc as relative.
Unfortunately, this meant that it was impossible to tell the actual
pc. The new code prints the map name as <anonymous:map_start> and
still prints the pc as relative.

In addition, add the start of the map for map names that begin with a
'[' character.

Bug: 25844836
Change-Id: Ie0b6149dde258fe13f0e5a3e5739d85374512f4b

2 files changed, 33 insertions, 10 deletions

diff --git a/libbacktrace/Backtrace.cpp b/libbacktrace/Backtrace.cpp
index 9ead452cf..555e8cf20 100644
--- a/libbacktrace/Backtrace.cpp
+++ b/libbacktrace/Backtrace.cpp
@@ -93,16 +93,26 @@ std::string Backtrace::FormatFrameData(size_t frame_num) {
 }
 
 std::string Backtrace::FormatFrameData(const backtrace_frame_data_t* frame) {
-  const char* map_name;
-  if (BacktraceMap::IsValid(frame->map) && !frame->map.name.empty()) {
-    map_name = frame->map.name.c_str();
+  uintptr_t relative_pc;
+  std::string map_name;
+  if (BacktraceMap::IsValid(frame->map)) {
+    relative_pc = BacktraceMap::GetRelativePc(frame->map, frame->pc);
+    if (!frame->map.name.empty()) {
+      map_name = frame->map.name.c_str();
+      if (map_name[0] == '[' && map_name[map_name.size() - 1] == ']') {
+        map_name.resize(map_name.size() - 1);
+        map_name += StringPrintf(":%" PRIPTR "]", frame->map.start);
+      }
+    } else {
+      map_name = StringPrintf("<anonymous:%" PRIPTR ">", frame->map.start);
+    }
   } else {
     map_name = "<unknown>";
+    relative_pc = frame->pc;
   }
 
-  uintptr_t relative_pc = BacktraceMap::GetRelativePc(frame->map, frame->pc);
-
-  std::string line(StringPrintf("#%02zu pc %" PRIPTR "  %s", frame->num, relative_pc, map_name));
+  std::string line(StringPrintf("#%02zu pc %" PRIPTR "  ", frame->num, relative_pc));
+  line += map_name;
   // Special handling for non-zero offset maps, we need to print that
   // information.
   if (frame->map.offset != 0) {
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 9ebd63913..ce04817db 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -775,16 +775,29 @@ TEST(libbacktrace, format_test) {
             backtrace->FormatFrameData(&frame));
 
   // Check map name empty, but exists.
-  frame.map.start = 1;
-  frame.map.end = 1;
+  frame.pc = 0xb0020;
+  frame.map.start = 0xb0000;
+  frame.map.end = 0xbffff;
   frame.map.load_base = 0;
 #if defined(__LP64__)
-  EXPECT_EQ("#01 pc 0000000000000001  <unknown>",
+  EXPECT_EQ("#01 pc 0000000000000020  <anonymous:00000000000b0000>",
 #else
-  EXPECT_EQ("#01 pc 00000001  <unknown>",
+  EXPECT_EQ("#01 pc 00000020  <anonymous:000b0000>",
 #endif
             backtrace->FormatFrameData(&frame));
 
+  // Check map name begins with a [.
+  frame.pc = 0xc0020;
+  frame.map.start = 0xc0000;
+  frame.map.end = 0xcffff;
+  frame.map.load_base = 0;
+  frame.map.name = "[anon:thread signal stack]";
+#if defined(__LP64__)
+  EXPECT_EQ("#01 pc 0000000000000020  [anon:thread signal stack:00000000000c0000]",
+#else
+  EXPECT_EQ("#01 pc 00000020  [anon:thread signal stack:000c0000]",
+#endif
+            backtrace->FormatFrameData(&frame));
 
   // Check relative pc is set and map name is set.
   frame.pc = 0x12345679;