simpleperf: support libraries without build ids when recording.

Simpleperf can download unstripped libraries on device and use them
for unwinding during recording, through `app_profiler.py -lib` and
`simpleperf record --symfs` options. But it doesn't support libraries
without build ids.

To support them:
1. In app_profiler.py, download libraries without build ids in native
   lib dir.
2. In DebugElfFileFinder in dso.cpp, check path with the same basename
   in symfs_dir.

Also add document for downloading unstripped libraries on device.

Bug: none
Test: run simpleperf_unit_test.
Test: run test.py.
Change-Id: I5d9015e683f2ecb992d425a42f1f7303307b2cea

1 files changed, 7 insertions, 2 deletions

diff --git a/simpleperf/dso.cpp b/simpleperf/dso.cpp
index ff3e41f8..6db0f6b7 100644
--- a/simpleperf/dso.cpp
+++ b/simpleperf/dso.cpp
@@ -135,14 +135,19 @@ std::string DebugElfFileFinder::FindDebugFile(const std::string& dso_path, bool
       }
     }
   }
-  // 2. Try concatenating symfs_dir and dso_path.
   if (!symfs_dir_.empty()) {
+    // 2. Try concatenating symfs_dir and dso_path.
     std::string path = GetPathInSymFsDir(dso_path);
     if (check_path(path)) {
       return path;
     }
+    // 3. Try concatenating symfs_dir and basename of dso_path.
+    path = symfs_dir_ + OS_PATH_SEPARATOR + android::base::Basename(dso_path);
+    if (check_path(path)) {
+      return path;
+    }
   }
-  // 3. Try concatenating /usr/lib/debug and dso_path.
+  // 4. Try concatenating /usr/lib/debug and dso_path.
   // Linux host can store debug shared libraries in /usr/lib/debug.
   if (check_path("/usr/lib/debug" + dso_path)) {
     return "/usr/lib/debug" + dso_path;