disassembler bug

[Roland McGrath <roland at redhat dot com>]

cf https://bugzilla.redhat.com/show_bug.cgi?id=469739

This manifests with:

	$ rpm -qf /usr/lib64/libavcodec.so.51
	ffmpeg-libs-0.4.9-0.52.20080908.fc10.x86_64
	$ eu-objdump -d /usr/lib64/libavcodec.so.51 > d
	eu-objdump: i386_disasm.c:354: x86_64_disasm: Assertion `avail > 0' failed.
	Aborted (core dumped)
	$ 

It first goes off the rails with a mis-disassembly.  But even if confused
and/or having bogus input, it shouldn't hit an assert.  So there are
probably two bugs to fix.  The first wrongly-shown instruction:

	$ objdump -d /tmp/foo.o

	/tmp/foo.o:     file format elf64-x86-64


	Disassembly of section .text:

	0000000000000000 <.text>:
	   0:	0f 0f 00 bf          	pavgusb (%rax),%mm0
	   4:	0f 0f 0c 30 bf       	pavgusb (%rax,%rsi,1),%mm1
	$ eu-objdump -d /tmp/foo.o
	/tmp/foo.o: elf64-elf_x86_64

	Disassembly of section .text:

	       0:    0f                       pop     %cs
	       1:    0f                       pop     %cs
	       2:    00 bf 0f 0f 0c 30        add     %bh,0x300c0f0f(%rdi)
	       8:    bf                       mov     (bad)

That is a big file full of wacky SSE or whatnot instructions, so probably a
good test to check that all the disassemblies from eu-objdump match those
from objdump, not just this first one I noticed.


Thanks,
Roland