In an arm target which is not in gcc svn (see http://gccsdk.riscos.info/) we have the following options defined in its .opt file:

--8<--
mlibscl
Target Report RejectNegative InverseMask(UNIXLIB,LIBSCL)
Compile with the SharedCLibrary headers

munixlib
Target Report RejectNegative Mask(UNIXLIB)
Compile with the UnixLib headers (default)

mmodule
Target Report RejectNegative Negative(munixlib) Mask(MODULE)
Target for RISC OS modules
--8<--

I.e. the mlibscl and munixlib options are exclusive and the option mmodule can only be used with mlibscl (munixlib is default).

When cross-compiling gcc 4.2.0 I get an ICE in the cancel_option() routine:

--8<--
/home/john/gccsdk/gccsdk_svn2/gcc4/arm-unknown-riscos/gcc/xgcc -B/home/john/gccsdk/gccsdk_svn2/gcc4/arm-unknown-riscos/./gcc/ -B/home/john/gccsdk/gccsdk_svn2/gcc4/arm-unknown-riscos/arm-unknown-riscos/libunixlib/ -B/home/john/gccsdk/gccsdk_svn2/gcc4/arm-unknown-riscos/arm-unknown-riscos/libunixlib/.libs/ -isystem /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/libunixlib/include -B/home/john/gccsdk/riscos2/cross/arm-unknown-riscos/bin/ -B/home/john/gccsdk/riscos2/cross/arm-unknown-riscos/lib/ -isystem /home/john/gccsdk/riscos2/cross/arm-unknown-riscos/include -isystem /home/john/gccsdk/riscos2/cross/arm-unknown-riscos/sys-include -L/home/john/gccsdk/gccsdk_svn2/gcc4/arm-unknown-riscos/./ld -O2 -O0 -g -DIN_GCC -DCROSS_COMPILE -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition -isystem ./include -mlibscl -mhard-float -mmodule -I. -Iscl/fpu/module -I/home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc -I/home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/scl/fpu/module -I/home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/../include -I/home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/../libcpp/include -I/home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/../libdecnumber -I../libdecnumber -c -o scl/fpu/module/crti-riscos.o -x assembler-with-cpp /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/config/arm/crti-riscos.asm

Program received signal SIGSEGV, Segmentation fault.
0x00000000004132a1 in cancel_option (opt_idx=35, next_opt_idx=1936942450, orig_next_opt_idx=563)
    at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/opts-common.c:119
119       if (cl_options [next_opt_idx].neg_index == opt_idx)
(gdb) where
#0  0x00000000004132a1 in cancel_option (opt_idx=35, next_opt_idx=1936942450, orig_next_opt_idx=563)
    at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/opts-common.c:119
#1  0x00000000004132f7 in cancel_option (opt_idx=35, next_opt_idx=-1, orig_next_opt_idx=563)
    at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/opts-common.c:123
#2  0x00000000004132f7 in cancel_option (opt_idx=35, next_opt_idx=576, orig_next_opt_idx=563)
    at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/opts-common.c:123
#3  0x00000000004132f7 in cancel_option (opt_idx=35, next_opt_idx=563, orig_next_opt_idx=563)
    at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/opts-common.c:123
#4  0x00000000004135de in prune_options (argcp=0x7fff5a200ef4, argvp=0x7fff5a200ee8)
    at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/opts-common.c:208
#5  0x000000000040e623 in main (argc=43, argv=0x7fff5a201168) at /home/john/gccsdk/gccsdk_svn2/gcc4/srcdir/gcc/gcc.c:6115
--8<--

Investigation learns me that the it goes wrong when calling cancel_option() for the mmodule option.  In the produced options.c file I have:

--8<--
Option 563:
  { "-mmodule",
    "Target for RISC OS modules",
    N_OPTS, 7, 576,
    CL_TARGET | CL_REJECT_NEGATIVE | CL_REPORT,
    &target_flags, CLVC_BIT_SET, MASK_MODULE },

Option 576:
  { "-munixlib",
    "Compile with the UnixLib headers (default)",
    N_OPTS, 8, -1,
    CL_TARGET | CL_REJECT_NEGATIVE | CL_REPORT,
    &target_flags, CLVC_BIT_SET, MASK_UNIXLIB },
--8<--

cancel_option() will recursively call itself when cl_options [next_opt_idx].neg_index != orig_next_opt_idx for the value cl_options [next_opt_idx].neg_index however when the option munixlib is reached, its neg_index is -1 which results in a nonsense situation to continue calling cancel_option().

My proposed fix is:

--8<--
--- gcc/opts-common.c.orig      2007-05-17 14:42:41.000000000 +0200
+++ gcc/opts-common.c   2007-05-17 14:42:21.000000000 +0200
@@ -119,7 +119,8 @@
   if (cl_options [next_opt_idx].neg_index == opt_idx)
     return true;

-  if (cl_options [next_opt_idx].neg_index != orig_next_opt_idx)
+  if (cl_options [next_opt_idx].neg_index >= 0
+      && cl_options [next_opt_idx].neg_index != orig_next_opt_idx)
     return cancel_option (opt_idx, cl_options [next_opt_idx].neg_index,
                          orig_next_opt_idx);
--8<--

which seems to solve my problem.