While working on something else, I found the following:

    /* FIXME (alloca): unsafe if baseclass is really really large. */
    gdb_byte *buf = alloca (TYPE_LENGTH (baseclass));

The attached patch replaces that with a xmalloc/xfree pair.

There are some differences I don't understand between the before- and 
after- gdb.sum files from make check--the diff -u of those files is also 
attached.