Bug 914253 patch 3 - Implement separate debug info for fix_linux_stack.py, including the addition of support for .note.gnu.build-id sections that fix-linux-stack.pl did not support. No review.

tools/rb/fix_linux_stack.py

@@ -23,6 +23,7 @@ import re
 import os
 import pty
 import termios
+from StringIO import StringIO
 
 class unbufferedLineConverter:
     """
@@ -51,7 +52,121 @@ class unbufferedLineConverter:
         assert unbufferedLineConverter("cut", ["-c3"]).convert("abcde") == "c"
         print "Pass"
 
+objdump_section_re = re.compile("^ [0-9a-f]* ([0-9a-f ]{8}) ([0-9a-f ]{8}) ([0-9a-f ]{8}) ([0-9a-f ]{8}).*")
+def elf_section(file, section):
+    """
+    Return the requested ELF section of the file as a str, represented
+    as a sequence of bytes.
+    """
+    # We can read the .gnu_debuglink section using either of:
+    #   objdump -s --section=.gnu_debuglink $file
+    #   readelf -x .gnu_debuglink $file
+    # Since readelf prints things backwards on little-endian platforms
+    # for some versions only (backwards on Fedora Core 6, forwards on
+    # Fedora 7), use objdump.
+    objdump = subprocess.Popen(['objdump', '-s', '--section=' + section, file],
+                               stdout=subprocess.PIPE,
+                               # redirect stderr so errors don't get printed
+                               stderr=subprocess.PIPE)
+    (objdump_stdout, objdump_stderr) = objdump.communicate()
+    if objdump.returncode != 0:
+        return None
+    result = ""
+    # Turn hexadecimal dump into the bytes it represents
+    for line in StringIO(objdump_stdout).readlines():
+        m = objdump_section_re.match(line)
+        if m:
+            for gnum in [0, 1, 2, 3]:
+                word = m.groups()[gnum]
+                if word != "        ":
+                    for idx in [0, 2, 4, 6]:
+                        result += chr(int(word[idx:idx+2], 16))
+    return result
+
+# FIXME: Hard-coded to gdb defaults (works on Fedora and Ubuntu).
+global_debug_dir = '/usr/lib/debug';
+
+endian_re = re.compile("\s*Data:\s+.*(little|big) endian.*$")
+
 def separate_debug_file_for(file):
+    """
+    Finds a separated file with the debug sections for a binary.  Such
+    files are commonly installed by debug packages on linux distros.
+    Rules for finding them are documented in:
+    https://sourceware.org/gdb/current/onlinedocs/gdb/Separate-Debug-Files.html
+    """
+    def have_debug_file(debugfile):
+        return os.path.isfile(debugfile)
+
+    endian = None
+    readelf = subprocess.Popen(['readelf', '-h', file],
+                               stdout=subprocess.PIPE)
+    for line in readelf.stdout.readlines():
+        m = endian_re.match(line)
+        if m:
+            endian = m.groups()[0]
+            break
+    readelf.terminate()
+    if endian is None:
+        sys.stderr.write("Could not determine endianness of " + file + "\n")
+        return None
+
+    def word32(s):
+        if type(s) != str or len(s) != 4:
+            raise StandardError("expected 4 byte string input")
+        s = list(s)
+        if endian == "big":
+            s.reverse()
+        return sum(map(lambda idx: ord(s[idx]) * (256 ** idx), range(0, 4)))
+
+    buildid = elf_section(file, ".note.gnu.build-id");
+    if buildid is not None:
+        # The build ID is an ELF note section, so it begins with a
+        # name size (4), a description size (size of contents), a
+        # type (3), and the name "GNU\0".
+        note_header = buildid[0:16]
+        buildid = buildid[16:]
+        #print word32(note_header[0:4])
+        #print word32(note_header[4:8])
+        #print len(buildid)
+        #print word32(note_header[8:12])
+        if word32(note_header[0:4]) != 4 or \
+           word32(note_header[4:8]) != len(buildid) or \
+           word32(note_header[8:12]) != 3 or \
+           note_header[12:16] != "GNU\0":
+            sys.stderr.write("malformed .note.gnu.build_id in " + file + "\n")
+        else:
+            buildid = "".join(map(lambda ch: "%02X" % ord(ch), buildid)).lower()
+            f = os.path.join(global_debug_dir, ".build-id", buildid[0:2], buildid[2:] + ".debug")
+            if have_debug_file(f):
+                return f
+
+    debuglink = elf_section(file, ".gnu_debuglink");
+    if debuglink is not None:
+        # The debuglink section contains a string, ending with a
+        # null-terminator and then 0 to three bytes of padding to fill the
+        # current 32-bit unit.  (This padding is usually null bytes, but
+        # I've seen null-null-H, on Ubuntu x86_64.)  This is followed by
+        # a 4-byte CRC.
+        debuglink_name = debuglink[:-4]
+        null_idx = debuglink_name.find("\0")
+        if null_idx == -1 or null_idx + 4 < len(debuglink_name):
+            sys.stderr.write("Malformed .gnu_debuglink in " + file + "\n")
+            return None
+        debuglink_name = debuglink_name[0:null_idx]
+
+        debuglink_crc = word32(debuglink[-4:])
+
+        dirname = os.path.dirname(file)
+        possible_files = [
+            os.path.join(dirname, debuglink_name),
+            os.path.join(dirname, ".debug", debuglink_name),
+            os.path.join(global_debug_dir, dirname.lstrip("/"), debuglink_name)
+        ]
+        for f in possible_files:
+            if have_debug_file(f):
+                # FIXME: Check the CRC!
+                return f
     return None
 
 addr2lines = {}