[ARM] Remove ARMv6S-M special casing

=== Context ===

This patch is part of a patch series to add support for ARMv8-R
architecture. Its purpose is to remove special casing for ARMv6S-M
autodetection.

=== Motivation ===

Currently, SWI and SVC mnemonics are enabled for ARMv4T and successor
architectures with extra checks in the handler function (do_t_swi) to
give an error message when ARMv6-M is targeted and some more special
casing in aeabi_set_public_attributes. This was made to exclude these
mnemonics for ARMv6-M unless the OS extension is in use.

However this logic is superfluous: there is already code to check
whether an instruction is available based on the feature bit it is part
of and whether the targeted architecture has that feature bit. This
patch aims at removing that unneeded complexity.

=== Patch description ===

The OS extension is already limited to the ARMv6-M architecture so all
this patch does is redefined availability of the ARM_EXT_OS feature bit
to not be present for ARM_ARCH_V6M. ARM_ARCH_V6SM does not need any
change either because it already includes ARM_EXT_OS.

The patch also make sure that the error message that was given by
do_t_swi when SWI/SVC is unavailable is still the same by detecting the
situation in md_assemble.

2017-06-24  Thomas Preud'homme  <thomas.preudhomme@arm.com>

gas/
	* config/tc-arm.c (arm_ext_v6m): Delete.
	(arm_ext_v7m): Delete.
	(arm_ext_m): Remove ARM_EXT_OS from the set of feature defined M
	profile.
	(arm_arch_v6m_only): Delete.
	(do_t_swi): Remove special case for ARMv6S-M.
	(md_assemble): Display error message previously in do_t_swi when
	SVC is not available.
	(insns): Guard swi and svc by arm_ext_os for Thumb mode.
	(aeabi_set_public_attributes): Remove special case for ARMv6S-M.

include/
	* opcode/arm.h (ARM_AEXT_V4TxM): Add ARM_EXT_OS bit to the set.
	(ARM_AEXT_V4T): Likewise.
	(ARM_AEXT_V5TxM): Likewise.
	(ARM_AEXT_V5T): Likewise.
	(ARM_AEXT_V6M): Mask off ARM_EXT_OS bit.

2 files changed, 24 insertions, 26 deletions

diff --git a/gas/ChangeLog b/gas/ChangeLog
index e5130e7..84dd4bf 100644
--- a/gas/ChangeLog
+++ b/gas/ChangeLog
@@ -1,3 +1,16 @@
+2017-06-24  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* config/tc-arm.c (arm_ext_v6m): Delete.
+	(arm_ext_v7m): Delete.
+	(arm_ext_m): Remove ARM_EXT_OS from the set of feature defined M
+	profile.
+	(arm_arch_v6m_only): Delete.
+	(do_t_swi): Remove special case for ARMv6S-M.
+	(md_assemble): Display error message previously in do_t_swi when
+	SVC is not available.
+	(insns): Guard swi and svc by arm_ext_os for Thumb mode.
+	(aeabi_set_public_attributes): Remove special case for ARMv6S-M.
+
 2017-05-11  Andrew Waterman  <andrew@sifive.com>
 
 	* config/tc-riscv.c (riscv_ip): Changes as_warn to as_bad for improper
diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
index 18d3a20..5eb088c 100644
--- a/gas/config/tc-arm.c
+++ b/gas/config/tc-arm.c
@@ -189,7 +189,6 @@ static const arm_feature_set arm_ext_v5j = ARM_FEATURE_CORE_LOW (ARM_EXT_V5J);
 static const arm_feature_set arm_ext_v6 = ARM_FEATURE_CORE_LOW (ARM_EXT_V6);
 static const arm_feature_set arm_ext_v6k = ARM_FEATURE_CORE_LOW (ARM_EXT_V6K);
 static const arm_feature_set arm_ext_v6t2 = ARM_FEATURE_CORE_LOW (ARM_EXT_V6T2);
-static const arm_feature_set arm_ext_v6m = ARM_FEATURE_CORE_LOW (ARM_EXT_V6M);
 static const arm_feature_set arm_ext_v6_notm =
   ARM_FEATURE_CORE_LOW (ARM_EXT_V6_NOTM);
 static const arm_feature_set arm_ext_v6_dsp =
@@ -207,7 +206,7 @@ static const arm_feature_set ATTRIBUTE_UNUSED arm_ext_v7m = ARM_FEATURE_CORE_LOW
 #endif
 static const arm_feature_set arm_ext_v8 = ARM_FEATURE_CORE_LOW (ARM_EXT_V8);
 static const arm_feature_set arm_ext_m =
-  ARM_FEATURE_CORE (ARM_EXT_V6M | ARM_EXT_OS | ARM_EXT_V7M,
+  ARM_FEATURE_CORE (ARM_EXT_V6M | ARM_EXT_V7M,
 		    ARM_EXT2_V8M | ARM_EXT2_V8M_MAIN);
 static const arm_feature_set arm_ext_mp = ARM_FEATURE_CORE_LOW (ARM_EXT_MP);
 static const arm_feature_set arm_ext_sec = ARM_FEATURE_CORE_LOW (ARM_EXT_SEC);
@@ -244,9 +243,6 @@ static const arm_feature_set fpu_any = FPU_ANY;
 static const arm_feature_set arm_arch_full ATTRIBUTE_UNUSED = ARM_FEATURE (-1, -1, -1);
 static const arm_feature_set arm_arch_t2 = ARM_ARCH_THUMB2;
 static const arm_feature_set arm_arch_none = ARM_ARCH_NONE;
-#ifdef OBJ_ELF
-static const arm_feature_set arm_arch_v6m_only = ARM_ARCH_V6M_ONLY;
-#endif
 
 static const arm_feature_set arm_cext_iwmmxt2 =
   ARM_FEATURE_COPROC (ARM_CEXT_IWMMXT2);
@@ -13120,17 +13116,6 @@ do_t_sxth (void)
 static void
 do_t_swi (void)
 {
-  /* We have to do the following check manually as ARM_EXT_OS only applies
-     to ARM_EXT_V6M.  */
-  if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v6m))
-    {
-      if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_os)
-	  /* This only applies to the v6m however, not later architectures.  */
-	  && ! ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v7))
-	as_bad (_("SVC is not permitted on this architecture"));
-      ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used, arm_ext_os);
-    }
-
   inst.reloc.type = BFD_RELOC_ARM_SWI;
 }
 
@@ -18471,7 +18456,10 @@ md_assemble (char *str)
 	  || (thumb_mode == 1
 	      && !ARM_CPU_HAS_FEATURE (variant, *opcode->tvariant)))
 	{
-	  as_bad (_("selected processor does not support `%s' in Thumb mode"), str);
+	  if (opcode->tencode == do_t_swi)
+	    as_bad (_("SVC is not permitted on this architecture"));
+	  else
+	    as_bad (_("selected processor does not support `%s' in Thumb mode"), str);
 	  return;
 	}
       if (inst.cond != COND_ALWAYS && !unified_syntax
@@ -19295,8 +19283,6 @@ static const struct asm_opcode insns[] =
  tC3("ldmia",	8900000, _ldmia,    2, (RRw, REGLST), ldmstm, t_ldmstm),
  tC3("ldmfd",	8900000, _ldmia,    2, (RRw, REGLST), ldmstm, t_ldmstm),
 
- TCE("swi",	f000000, df00,     1, (EXPi),        swi, t_swi),
- TCE("svc",	f000000, df00,     1, (EXPi),        swi, t_swi),
  tCE("b",	a000000, _b,	   1, (EXPr),	     branch, t_branch),
  TCE("bl",	b000000, f000f800, 1, (EXPr),	     bl, t_branch23),
 
@@ -19324,6 +19310,12 @@ static const struct asm_opcode insns[] =
  TCE("rsb",	0600000, ebc00000, 3, (RR, oRR, SH), arit, t_rsb),
  TC3("rsbs",	0700000, ebd00000, 3, (RR, oRR, SH), arit, t_rsb),
 
+#undef THUMB_VARIANT
+#define THUMB_VARIANT  & arm_ext_os
+
+ TCE("swi",	f000000, df00,     1, (EXPi),        swi, t_swi),
+ TCE("svc",	f000000, df00,     1, (EXPi),        swi, t_swi),
+
 #undef  THUMB_VARIANT
 #define THUMB_VARIANT  & arm_ext_v6
 
@@ -26804,13 +26796,6 @@ aeabi_set_public_attributes (void)
       if (ARM_CPU_HAS_FEATURE (thumb_arch_used, arm_arch_any))
 	ARM_MERGE_FEATURE_SETS (flags, flags, arm_ext_v4t);
 
-      /* We need to make sure that the attributes do not identify us as v6S-M
-	 when the only v6S-M feature in use is the Operating System
-	 Extensions.  */
-      if (ARM_CPU_HAS_FEATURE (flags, arm_ext_os))
-	if (!ARM_CPU_HAS_FEATURE (flags, arm_arch_v6m_only))
-	  ARM_CLEAR_FEATURE (flags, flags, arm_ext_os);
-
       /* Code run during relaxation relies on selected_cpu being set.  */
       selected_cpu = flags;
     }