Using e.g.

	.arch_extension simd
	.arch_extension nocrypto

so far resulted in SIMD support getting disabled, which I can't see being
the purpose of the "no"-prefixed variants of architecture extension
specifications.

Of course it is questionable whether the current, counter intuitive
behavior needs to be retained, and the new behavior perhaps be made work
through e.g. a newly recognized "no-" prefix.

gas/
2013-04-08  Jan Beulich <jbeulich@suse.com>

	* gas/config/tc-arm.c (struct arm_option_extension_value_table):
	Split field "value" into fields "merge_value" and "clear_value".
	(arm_extensions): Adjust initializer accordingly.

--- 2013-04-08/gas/config/tc-arm.c
+++ 2013-04-08/gas/config/tc-arm.c
@@ -24064,40 +24064,51 @@ struct arm_option_extension_value_table
 {
   char *name;
   size_t name_len;
-  const arm_feature_set value;
+  const arm_feature_set merge_value;
+  const arm_feature_set clear_value;
   const arm_feature_set allowed_archs;
 };
 
 /* The following table must be in alphabetical order with a NULL last entry.
    */
-#define ARM_EXT_OPT(N, V, AA) { N, sizeof (N) - 1, V, AA }
+#define ARM_EXT_OPT(N, M, C, AA) { N, sizeof (N) - 1, M, C, AA }
 static const struct arm_option_extension_value_table arm_extensions[] =
 {
-  ARM_EXT_OPT ("crc",  ARCH_CRC_ARMV8, ARM_FEATURE (ARM_EXT_V8, 0)),
+  ARM_EXT_OPT ("crc",  ARCH_CRC_ARMV8, ARCH_CRC_ARMV8,
+				   ARM_FEATURE (ARM_EXT_V8, 0)),
   ARM_EXT_OPT ("crypto", FPU_ARCH_CRYPTO_NEON_VFP_ARMV8,
+			 ARM_FEATURE (0, FPU_CRYPTO_ARMV8),
 				   ARM_FEATURE (ARM_EXT_V8, 0)),
-  ARM_EXT_OPT ("fp",     FPU_ARCH_VFP_ARMV8,
+  ARM_EXT_OPT ("fp",     FPU_ARCH_VFP_ARMV8, ARM_FEATURE (0, FPU_VFP_ARMV8),
 				   ARM_FEATURE (ARM_EXT_V8, 0)),
   ARM_EXT_OPT ("idiv",	ARM_FEATURE (ARM_EXT_ADIV | ARM_EXT_DIV, 0),
+			ARM_FEATURE (ARM_EXT_ADIV | ARM_EXT_DIV, 0),
 				   ARM_FEATURE (ARM_EXT_V7A | ARM_EXT_V7R, 0)),
-  ARM_EXT_OPT ("iwmmxt",ARM_FEATURE (0, ARM_CEXT_IWMMXT),	ARM_ANY),
-  ARM_EXT_OPT ("iwmmxt2",
-			ARM_FEATURE (0, ARM_CEXT_IWMMXT2),	ARM_ANY),
-  ARM_EXT_OPT ("maverick",
-                        ARM_FEATURE (0, ARM_CEXT_MAVERICK),	ARM_ANY),
+  ARM_EXT_OPT ("iwmmxt",ARM_FEATURE (0, ARM_CEXT_IWMMXT),
+			ARM_FEATURE (0, ARM_CEXT_IWMMXT), ARM_ANY),
+  ARM_EXT_OPT ("iwmmxt2", ARM_FEATURE (0, ARM_CEXT_IWMMXT2),
+			  ARM_FEATURE (0, ARM_CEXT_IWMMXT2), ARM_ANY),
+  ARM_EXT_OPT ("maverick", ARM_FEATURE (0, ARM_CEXT_MAVERICK),
+			   ARM_FEATURE (0, ARM_CEXT_MAVERICK), ARM_ANY),
   ARM_EXT_OPT ("mp",	ARM_FEATURE (ARM_EXT_MP, 0),
+			ARM_FEATURE (ARM_EXT_MP, 0),
 				   ARM_FEATURE (ARM_EXT_V7A | ARM_EXT_V7R, 0)),
   ARM_EXT_OPT ("simd",   FPU_ARCH_NEON_VFP_ARMV8,
+			 ARM_FEATURE(0, FPU_NEON_ARMV8),
 				   ARM_FEATURE (ARM_EXT_V8, 0)),
   ARM_EXT_OPT ("os",	ARM_FEATURE (ARM_EXT_OS, 0),
+			ARM_FEATURE (ARM_EXT_OS, 0),
 				   ARM_FEATURE (ARM_EXT_V6M, 0)),
   ARM_EXT_OPT ("sec",	ARM_FEATURE (ARM_EXT_SEC, 0),
+			ARM_FEATURE (ARM_EXT_SEC, 0),
 				   ARM_FEATURE (ARM_EXT_V6K | ARM_EXT_V7A, 0)),
   ARM_EXT_OPT ("virt",	ARM_FEATURE (ARM_EXT_VIRT | ARM_EXT_ADIV
 				     | ARM_EXT_DIV, 0),
+			ARM_FEATURE (ARM_EXT_VIRT, 0),
 				   ARM_FEATURE (ARM_EXT_V7A, 0)),
-  ARM_EXT_OPT ("xscale",ARM_FEATURE (0, ARM_CEXT_XSCALE),	ARM_ANY),
-  { NULL, 0, ARM_ARCH_NONE, ARM_ARCH_NONE }
+  ARM_EXT_OPT ("xscale",ARM_FEATURE (0, ARM_CEXT_XSCALE),
+			ARM_FEATURE (0, ARM_CEXT_XSCALE), ARM_ANY),
+  { NULL, 0, ARM_ARCH_NONE, ARM_ARCH_NONE, ARM_ARCH_NONE }
 };
 #undef ARM_EXT_OPT
 
@@ -24272,9 +24283,9 @@ arm_parse_extension (char *str, const ar
 
 	    /* Add or remove the extension.  */
 	    if (adding_value)
-	      ARM_MERGE_FEATURE_SETS (*ext_set, *ext_set, opt->value);
+	      ARM_MERGE_FEATURE_SETS (*ext_set, *ext_set, opt->merge_value);
 	    else
-	      ARM_CLEAR_FEATURE (*ext_set, *ext_set, opt->value);
+	      ARM_CLEAR_FEATURE (*ext_set, *ext_set, opt->clear_value);
 
 	    break;
 	  }
@@ -24994,9 +25005,10 @@ s_arm_arch_extension (int ignored ATTRIB
 	  }
 
 	if (adding_value)
-	  ARM_MERGE_FEATURE_SETS (selected_cpu, selected_cpu, opt->value);
+	  ARM_MERGE_FEATURE_SETS (selected_cpu, selected_cpu,
+				  opt->merge_value);
 	else
-	  ARM_CLEAR_FEATURE (selected_cpu, selected_cpu, opt->value);
+	  ARM_CLEAR_FEATURE (selected_cpu, selected_cpu, opt->clear_value);
 
 	mcpu_cpu_opt = &selected_cpu;
 	ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);