GNU bug report logs - #6551
[PATCH] hash: extend module to deal with non-pointer keys

Previous Next

Full log

View this message in rfc822 format

From: Jim Meyering <jim <at> meyering.net>
To: Paul Eggert <eggert <at> CS.UCLA.EDU>
Cc: bug-coreutils <at> gnu.org, bug-gnulib <at> gnu.org, 6524 <at> debbugs.gnu.org
Subject: bug#6551: [PATCH] hash: extend module to deal with non-pointer keys
Date: Fri, 02 Jul 2010 21:17:20 +0200

Paul Eggert wrote:

> On 07/01/10 15:59, Jim Meyering wrote:
>
>> Can you give me a backtrace?
>> Even if your patch is clearly better, I'd like to know
>> how my code is malfunctioning.
>
> Sure.  This uses your older patch, not the newer gnulib one.
>
> Program received signal SIGABRT, Aborted.
> 0x0012d422 in __kernel_vsyscall ()
> (gdb) where
> #0  0x0012d422 in __kernel_vsyscall ()
> #1  0x00158651 in *__GI_raise (sig=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:64
> #2  0x0015ba82 in *__GI_abort () at abort.c:92
> #3  0x08054826 in hash_insert0 (table=0x805f208, entry=0x8017384d, matched_ent=0x0) at hash.c:1078
> #4  0x0804bdba in di_set_insert (dis=0x805e2f4, dev=2049, ino=380435) at di-set.c:264
> #5  0x0804ab0f in hash_ins (argc=52, argv=0xbffff304) at du.c:335
> #6  process_file (argc=52, argv=0xbffff304) at du.c:467
> #7  du_files (argc=52, argv=0xbffff304) at du.c:592
> #8  main (argc=52, argv=0xbffff304) at du.c:962
>
> The test case, by the way, is "./du ../../cu*", where the
> globbing pattern expands to 51 directories, each a copy of coreutils,
> with several hard links because many are git clones of each other.
> Arf arf!  (I'm eating my own dog food.)

Thanks again for the report.
However, while I was able to reproduce it (on Paul's system)
and debug it, it appears to be due to a miscompilation of di-set.o
when using a private copy of gcc-4.5.0.  When I recompiled
that one file with gcc-Ubuntu 4.4.3-4ubuntu5 and -g -O2
or with 4.5.0 and -g -O, the code works as expected.

The problem arose in the di_ent_compare function and its use
of the tiny decode_ptr.  For the record, here they are:

    static struct di_ent
    decode_ptr (struct di_ent const *v)
    {
      if (!is_encoded_ptr (v))
        return *v;

      struct di_ent di;
      di.u.ptr = (void *) v;
      return di;
    }

    /* Compare two di_ent structs.
       Return true if they are the same.  */
    static bool
    di_ent_compare (void const *x, void const *y)
    {
      struct di_ent a = decode_ptr (x);
      struct di_ent b = decode_ptr (y);
      if (a.u.di4.mode != b.u.di4.mode)
        return false;

      if (a.u.di4.mode == DI_MODE_4)
        return (a.u.di4.short_ino == b.u.di4.short_ino
                && a.u.di4.mapped_dev == b.u.di4.mapped_dev);

      if (a.u.di8.mode == DI_MODE_8)
        return (a.u.di8.short_ino == b.u.di8.short_ino
                && a.u.di8.mapped_dev == b.u.di8.mapped_dev);

      return (a.u.full.ino == b.u.full.ino
              && a.u.full.dev == b.u.full.dev);
    }

Even though they're obviously distinct encoded values (see the
hexadecimal values below), di_ent_compare (aka table->comparator)
reports they're equal when using gcc-4.5.0 -g -O2, and that causes
the failed assertion:

    (gdb) p table->comparator (entry, bucket->data)
    $9 = true
    (gdb) p bucket->data
    $10 = (void *) 0x80143c4d
    (gdb) p entry
    $11 = (const void *) 0x80173851

I expect to push this series shortly.
Paul, if you end up improving further, you're welcome to revert
any pieces that are no longer used.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.