gdb: take libstdc++ pretty printers from host, not external/

libstdc++ comes with a python script to help gdb pretty-print some useful
C++ types (unique_ptr, vector, etc.). Our current gdb script takes this
script from external/, but unfortunately the script we have in external/
is from Fedora 20, written for Python 2, while some systems' gdb have
Python 3 so this script doesn't work.

The more sensible thing to do - given that we're already using (by default)
the build machine's libstdc++, and its gdb, is to run the script installed
on the build machine. This is what this patch does, unfortunately in an
ugly way and not a very robust way (namely, if two versions of
libstdc++ are installed, it picks one arbitrarily). But I can't figure
out a cleaner way to do this.

Fixes cloudius/gcc-bin/#1

Signed-off-by: Nadav Har'El <[email protected]>
Signed-off-by: Pekka Enberg <[email protected]>

scripts/loader.py

@@ -4,6 +4,7 @@
 import re
 import os, os.path
 import heapq
+import fnmatch
 from glob import glob
 from collections import defaultdict
 
@@ -1012,12 +1013,31 @@ def continue_handler(event):
 gdb.events.cont.connect(continue_handler)
 
 def setup_libstdcxx():
-    gcc = external + '/gcc.bin'
-    sys.path += [gcc + '/usr/share/gdb/auto-load/usr/lib64',
-                 glob(gcc + '/usr/share/gcc-*/python')[0],
-                 ]
-    main = glob(gcc + '/usr/share/gdb/auto-load/usr/lib64/libstdc++.so.*.py')[0]
-    exec(compile(open(main).read(), main, 'exec'))
+    # A libstdc++ installation is normally acommpanied by a python script
+    # like /usr/share/gdb/auto-load/usr/lib64/libstdc++.so.6.0.20-gdb.py
+    # to be loaded into gdb and helps pretty-print various STL types in gdb.
+    # Normally, this script is automatically loaded by gdb when the
+    # "libstdc++.so.6.0.20" shared object is loaded into the debugger.
+    # But because OSv is statically linked, we miss that auto-loading, so we
+    #  need to look for, and run, this script explicitly.
+    sys.path += [glob('/usr/share/gcc-*/python')[0]]
+    for base, dirnames, filenames in os.walk(gdb.PYTHONDIR + '/../auto-load'):
+        for filename in fnmatch.filter(filenames, 'libstdc++.so.*-gdb.py'):
+            script = os.path.join(base, filename)
+            exec(compile(open(script).read(), script, 'exec'))
+            return
+    # The following commented code is similar, but takes the python script
+    # from external/ instead of the one installed on the system. This might
+    # be useful if "make build_env=external" was used. However, there's a
+    # snag - the Python script we have in external/ might not be compatible
+    # with the version of Python installed on the system (there's right now
+    # a transition between Python 2 and Python 3 making things difficult).
+    #gcc = external + '/gcc.bin'
+    #sys.path += [gcc + '/usr/share/gdb/auto-load/usr/lib64',
+    #             glob(gcc + '/usr/share/gcc-*/python')[0],
+    #             ]
+    #main = glob(gcc + '/usr/share/gdb/auto-load/usr/lib64/libstdc++.so.*.py')[0]
+    #exec(compile(open(main).read(), main, 'exec'))
 
 def sig_to_string(sig):
     '''Convert a tracepoing signature to a string'''