[hjl@gnu-6 bitfield]$ make
/usr/gcc-4.4-ix86/bin/gcc -g   -c -o main.o main.c
/usr/gcc-4.4-ix86/bin/gcc -g   -c -o i386-opc.o i386-opc.c
/usr/gcc-4.4-ix86/bin/gcc -o main main.o i386-opc.o
./gdb -batch -x gdb.cmd main
Breakpoint 1 at 0x4004a8: file main.c, line 8.

Breakpoint 1, main () at main.c:8
8		  i386_optab[0].opcode_modifier.modrm);
$1 = {d = 1, w = 1, s = 0, modrm = 1, shortform = 0, jump = 0, jumpdword = 0, 
  jumpbyte = 0, jumpintersegment = 0, floatmf = 0, floatr = 0, floatd = 0, 
  size16 = 0, size32 = 0, size64 = 0, ignoresize = 0, defaultsize = 0, 
  no_bsuf = 0, no_wsuf = 0, no_lsuf = 0, no_ssuf = 1, no_qsuf = 0, 
  no_ldsuf = 1, fwait = 0, isstring = 0, regkludge = 0, firstxmm0 = 0, 
  implicit1stxmm0 = 0, byteokintel = 0, todword = 0, toqword = 0, 
  addrprefixop0 = 0, isprefix = 0, immext = 0, norex64 = 0, rex64 = 0, 
  ugh = 0, vex = 0, vex256 = 0, vexnds = 0, vexndd = 0, vexw0 = 0, vexw1 = 0, 
  vex0f = 0, vex0f38 = 0, vex0f3a = 0, vex3sources = 0, veximmext = 0, 
  sse2avx = 0, noavx = 0, oldgcc = 0, attmnemonic = 0, attsyntax = 0, 
  intelsyntax = 0}
$2 = 0
i386_optab[0].opcode_modifier.modrm: 1

Program exited normally.
[hjl@gnu-6 bitfield]$ 

i386_optab[0].opcode_modifier.modrm should be 1 not 0.

The testcase is at

http://sourceware.org/bugzilla/attachment.cgi?id=4152&action=view