Bug 914253 patch 9 - Implement CRC checking for .gnu_debuglink section. No review.

This is needed to avoid regressions relative to the perl version because
the perl version failed, due to a missing /, to properly examine two of
the paths, one of which often yields the same filename as the original
file (but whose CRC will fail).

I've tested that this CRC calculation succeeds in cases where it should
succeed.

The observed CRC check failures (so far) on my Ubuntu 14.04 system are
the following links:
  /lib/x86_64-linux-gnu/libc.so.6 -> /lib/x86_64-linux-gnu/libc-2.19.so
  /lib/x86_64-linux-gnu/libpthread.so.0 -> /lib/x86_64-linux-gnu/libpthread-2.19.so
  /usr/lib/x86_64-linux-gnu/libgdk-x11-2.0.so.0 -> /usr/lib/x86_64-linux-gnu/libgdk-x11-2.0.so.0.2400.23
  /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0 -> /usr/lib/x86_64-linux-gnu/libgtk-x11-2.0.so.0.2400.23
which succeed on a later possibility in /usr/lib/debug/.  But optimizing
to check f != file before checking the CRC wouldn't help because of the
naming differences due to symlinks, so I didn't bother.  If we ever want
to optimize away the time doing the CRC checks for these failures, we
could do so by checking if the files are the same path *after* resolving
symlinks.

DONTBUILD

tools/rb/fix-linux-stack.pl

@@ -191,6 +191,7 @@ sub separate_debug_file_for($) {
         $global_debug_dir . dirname($file) . '/' . $basename
     );
     foreach my $result (@possible_results) {
+        print "$file $result " . (-f $result) . "\n";
         if (-f $result) {
             # XXX We should check the hash.
             return $result;

tools/rb/fix_linux_stack.py

@@ -88,6 +88,76 @@ global_debug_dir = '/usr/lib/debug';
 
 endian_re = re.compile("\s*Data:\s+.*(little|big) endian.*$")
 
+# Table of 256 values, per documentation of .gnu_debuglink sections.
+gnu_debuglink_crc32_table = [
+    0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
+    0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
+    0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
+    0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
+    0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
+    0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
+    0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
+    0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
+    0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
+    0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
+    0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
+    0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+    0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
+    0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
+    0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
+    0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
+    0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
+    0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
+    0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
+    0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
+    0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
+    0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
+    0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
+    0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+    0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
+    0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
+    0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
+    0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
+    0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
+    0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
+    0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
+    0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
+    0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
+    0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
+    0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
+    0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+    0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
+    0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
+    0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
+    0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
+    0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
+    0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
+    0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
+    0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
+    0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
+    0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
+    0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
+    0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+    0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
+    0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
+    0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
+    0x2d02ef8d
+]
+
+def gnu_debuglink_crc32(stream):
+    # Note that treats bitwise operators as though integers have an
+    # infinite number of bits (and thus such that negative integers
+    # 1-pad out to infinity).
+    crc = 0xffffffff
+    while True:
+        # Choose to read in 4096 byte chunks.
+        bytes = stream.read(4096)
+        if len(bytes) == 0:
+            break
+        for byte in bytes:
+            crc = gnu_debuglink_crc32_table[(crc ^ ord(byte)) & 0xff] ^ (crc >> 8)
+    return ~crc & 0xffffffff
+
 def separate_debug_file_for(file):
     """
     Finds a separated file with the debug sections for a binary.  Such
@@ -161,8 +231,11 @@ def separate_debug_file_for(file):
         ]
         for f in possible_files:
             if have_debug_file(f):
-                # FIXME: Check the CRC!
-                return f
+                fio = open(f, mode="r")
+                file_crc = gnu_debuglink_crc32(fio)
+                fio.close()
+                if file_crc == debuglink_crc:
+                    return f
     return None
 
 elf_type_re = re.compile("^\s*Type:\s+(\S+)")