[PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Julian Brown]

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Hi,

This patch fixes the case where the diagnostic on attempting to assemble 
files containing ARM instructions on processors which don't support them 
isn't very helpful (e.g. "instruction not supported -- `nop'"). Thumb 
mode is made the default on such cores, and attempts to use the ".arm" 
directive or ARM instructions is faulted.

Tested with "make check" with cross to arm-none-eabi, with a small test 
case added.

OK to apply on mainline? CSL branch?

Cheers,

Julian

ChangeLog (gas):

     * config/tc-arm.c (arm_thumb_only, arm_thumb_only_except): Add
     static vars.
     (md_assemble): Disable ARM instructions on non-ARM-supporting cores.
     (autoselect_thumb_from_cpu_variant): New function. Switch on Thumb
     mode automatically based on cpu variant.
     (md_begin): Call above function.
     (s_arm_cpu, s_arm_arch): Likewise.

ChangeLog (gas/testsuite):

     * gas/arm/noarm.s: Add test for disabled ARM insns.
     * gas/arm/noarm.d: Drive test for above.
     * gas/arm/noarm.l: Expected error output.

ChangeLog (include/opcode):

     * arm.h (THUMB_ONLY): New macro. Architectures which support only
     Thumb instructions.
     (THUMB_ONLY_EXCEPT): Bits set here negate the above cases.

[-- Attachment #2: v7m-no-arm-2 --]
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Index: gas/config/tc-arm.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-arm.c,v
retrieving revision 1.250.2.15
diff -c -p -r1.250.2.15 tc-arm.c
*** gas/config/tc-arm.c	5 May 2006 18:31:28 -0000	1.250.2.15
--- gas/config/tc-arm.c	11 May 2006 21:13:09 -0000
*************** static const arm_feature_set fpu_neon_ex
*** 215,220 ****
--- 215,224 ----
  static const arm_feature_set fpu_vfp_v3_or_neon_ext =
    ARM_FEATURE (0, FPU_NEON_EXT_V1 | FPU_VFP_EXT_V3);
  
+ static const arm_feature_set arm_thumb_only = ARM_FEATURE (THUMB_ONLY, 0);
+ static const arm_feature_set arm_thumb_only_except =
+   ARM_FEATURE (THUMB_ONLY_EXCEPT, 0);
+ 
  static int mfloat_abi_opt = -1;
  /* Record user cpu selection for object attributes.  */
  static arm_feature_set selected_cpu = ARM_ARCH_NONE;
*************** md_assemble (char *str)
*** 13484,13490 ****
  	ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
  				arm_ext_v6t2);
      }
!   else
      {
        /* Check that this instruction is supported for this CPU.  */
        if (!opcode->avariant ||
--- 13488,13495 ----
  	ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
  				arm_ext_v6t2);
      }
!   else if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_thumb_only)
!            || ARM_CPU_HAS_FEATURE (cpu_variant, arm_thumb_only_except))
      {
        /* Check that this instruction is supported for this CPU.  */
        if (!opcode->avariant ||
*************** md_assemble (char *str)
*** 13517,13522 ****
--- 13522,13532 ----
  	ARM_MERGE_FEATURE_SETS (arm_arch_used, arm_arch_used,
  				*opcode->avariant);
      }
+   else
+     {
+       as_bad (_("attempt to use ARM instruction on Thumb-only core `%s'"), str);
+       return;
+     }
    output_inst (str);
  }
  
*************** set_constant_flonums (void)
*** 18296,18301 ****
--- 18306,18322 ----
        abort ();
  }
  
+ /* Auto-select Thumb mode if it's the only available instruction set for the
+    given architecture.  */
+ 
+ static void
+ autoselect_thumb_from_cpu_variant (void)
+ {
+   if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_thumb_only)
+       && !ARM_CPU_HAS_FEATURE (cpu_variant, arm_thumb_only_except))
+     opcode_select (16);
+ }
+ 
  void
  md_begin (void)
  {
*************** md_begin (void)
*** 18396,18401 ****
--- 18417,18424 ----
  
    ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
  
+   autoselect_thumb_from_cpu_variant ();
+ 
    arm_arch_used = thumb_arch_used = arm_arch_none;
  
  #if defined OBJ_COFF || defined OBJ_ELF
*************** s_arm_cpu (int ignored ATTRIBUTE_UNUSED)
*** 19457,19462 ****
--- 19480,19486 ----
  	    selected_cpu_name[i] = 0;
  	  }
  	ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
+         autoselect_thumb_from_cpu_variant ();
  	*input_line_pointer = saved_char;
  	demand_empty_rest_of_line ();
  	return;
*************** s_arm_arch (int ignored ATTRIBUTE_UNUSED
*** 19490,19495 ****
--- 19514,19520 ----
  	selected_cpu = opt->value;
  	strcpy(selected_cpu_name, opt->name);
  	ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
+         autoselect_thumb_from_cpu_variant ();
  	*input_line_pointer = saved_char;
  	demand_empty_rest_of_line ();
  	return;
Index: gas/testsuite/gas/arm/noarm.d
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.d
diff -N gas/testsuite/gas/arm/noarm.d
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.d	11 May 2006 21:13:09 -0000
***************
*** 0 ****
--- 1,3 ----
+ # name: Disallow ARM instructions on V7M
+ # as: 
+ # error-output: noarm.l
Index: gas/testsuite/gas/arm/noarm.l
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.l
diff -N gas/testsuite/gas/arm/noarm.l
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.l	11 May 2006 21:13:09 -0000
***************
*** 0 ****
--- 1,3 ----
+ [^:]*: Assembler messages:
+ [^:]*:11: Error: selected processor does not support ARM opcodes
+ [^:]*:12: Error: attempt to use ARM instruction on Thumb-only core `nop'
Index: gas/testsuite/gas/arm/noarm.s
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.s
diff -N gas/testsuite/gas/arm/noarm.s
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.s	11 May 2006 21:13:09 -0000
***************
*** 0 ****
--- 1,12 ----
+         .arch armv7a
+         .syntax unified
+ 	.text
+ func:
+ 	nop
+ 	movw r0, #0
+ 
+ 	.arch armv7
+ 	nop
+ 	movw r0, #0
+ 	.arm
+ 	nop
Index: include/opcode/arm.h
===================================================================
RCS file: /cvs/src/src/include/opcode/arm.h,v
retrieving revision 1.9.2.1
diff -c -p -r1.9.2.1 arm.h
*** include/opcode/arm.h	3 Apr 2006 00:03:34 -0000	1.9.2.1
--- include/opcode/arm.h	11 May 2006 21:13:10 -0000
***************
*** 45,50 ****
--- 45,55 ----
  #define ARM_EXT_V7R	 0x00200000	/* Arm V7R.                */
  #define ARM_EXT_V7M	 0x00400000	/* Arm V7M.                */
  
+ /* A bitmask of architecture versions which support only Thumb instructions,
+    and exceptions containing bits which nullify that situation.  */
+ #define THUMB_ONLY	  (ARM_EXT_V7 | ARM_EXT_V7M)
+ #define THUMB_ONLY_EXCEPT (ARM_EXT_V7A | ARM_EXT_V7R)
+ 
  /* Co-processor space extensions.  */
  #define ARM_CEXT_XSCALE   0x00000001	/* Allow MIA etc.          */
  #define ARM_CEXT_MAVERICK 0x00000002	/* Use Cirrus/DSP coprocessor.  */

Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Paul Brook]

On Thursday 11 May 2006 22:23, Julian Brown wrote:
> + #define THUMB_ONLY      (ARM_EXT_V7 | ARM_EXT_V7M)
> + #define THUMB_ONLY_EXCEPT (ARM_EXT_V7A | ARM_EXT_V7R)

I don't think these are necessary.  In opcode_select we already have:

          if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
            as_bad (_("selected processor does not support ARM opcodes"));

That condition should be ok whenever we need to check for a Thumb-only core.

> *************** md_begin (void)
> *** 18396,18401 ****
> --- 18417,18424 ----
>  
>     ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
>  
> +   autoselect_thumb_from_cpu_variant ();
> +
>     arm_arch_used = thumb_arch_used = arm_arch_none;

Defaulting to thumb mode if a Thumb only core is specified on the commandline 
ok I guess, however...
  
>   #if defined OBJ_COFF || defined OBJ_ELF
> *************** s_arm_cpu (int ignored ATTRIBUTE_UNUSED)
> *** 19457,19462 ****
> --- 19480,19486 ----
>             selected_cpu_name[i] = 0;
>           }
>         ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
> +         autoselect_thumb_from_cpu_variant ();

I don't think making .arch armv7 imply .thumb is a good idea. 
If we do this we should also make .arch armv4 imply .arm.

Paul

Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Paul Brook]

On Thursday 11 May 2006 22:23, Julian Brown wrote:
> + #define THUMB_ONLY      (ARM_EXT_V7 | ARM_EXT_V7M)
> + #define THUMB_ONLY_EXCEPT (ARM_EXT_V7A | ARM_EXT_V7R)

I don't think these are necessary.  In opcode_select we already have:

          if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
            as_bad (_("selected processor does not support ARM opcodes"));

That condition should be ok whenever we need to check for a Thumb-only core.

> *************** md_begin (void)
> *** 18396,18401 ****
> --- 18417,18424 ----
>  
>     ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
>  
> +   autoselect_thumb_from_cpu_variant ();
> +
>     arm_arch_used = thumb_arch_used = arm_arch_none;

Defaulting to thumb mode if a Thumb only core is specified on the commandline 
ok I guess, however...
  
>   #if defined OBJ_COFF || defined OBJ_ELF
> *************** s_arm_cpu (int ignored ATTRIBUTE_UNUSED)
> *** 19457,19462 ****
> --- 19480,19486 ----
>             selected_cpu_name[i] = 0;
>           }
>         ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
> +         autoselect_thumb_from_cpu_variant ();

I don't think making .arch armv7 imply .thumb is a good idea. 
If we do this we should also make .arch armv4 imply .arm.

Paul

Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Julian Brown]

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Hi,

Paul Brook wrote:
> On Thursday 11 May 2006 22:23, Julian Brown wrote:
> 
>>+ #define THUMB_ONLY      (ARM_EXT_V7 | ARM_EXT_V7M)
>>+ #define THUMB_ONLY_EXCEPT (ARM_EXT_V7A | ARM_EXT_V7R)
> 
> I don't think these are necessary.  In opcode_select we already have:
> 
>           if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
>             as_bad (_("selected processor does not support ARM opcodes"));
> 
> That condition should be ok whenever we need to check for a Thumb-only core.

Yeah, that does make things simpler -- this version of the patch uses 
arm_ext_v1 as a condition instead.

> Defaulting to thumb mode if a Thumb only core is specified on the commandline 
> ok I guess, however...

> I don't think making .arch armv7 imply .thumb is a good idea. 
> If we do this we should also make .arch armv4 imply .arm.

OK, I've only made the auto-selection happen for command-line arch/cpu 
selection only. That probably has less potential for confusion.

Patch re-tested. OK to apply now?

Cheers,

Julian

ChangeLog:

ChangeLog (gas):

     * config/tc-arm.c (md_assemble): Improve diagnostic when attempting
     to use ARM instructions on non-ARM-supporting cores.
     (autoselect_thumb_from_cpu_variant): New function. Switch on Thumb
     mode automatically based on cpu variant.
     (md_begin): Call above function.

ChangeLog (gas/testsuite):

     * gas/arm/noarm.s: Add test for disabled ARM insns.
     * gas/arm/noarm.d: Drive test for above.
     * gas/arm/noarm.l: Expected error output.

[-- Attachment #2: v7m-no-arm-3 --]
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Index: gas/config/tc-arm.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-arm.c,v
retrieving revision 1.250.2.15
diff -c -p -r1.250.2.15 tc-arm.c
*** gas/config/tc-arm.c	5 May 2006 18:31:28 -0000	1.250.2.15
--- gas/config/tc-arm.c	12 May 2006 00:12:05 -0000
*************** md_assemble (char *str)
*** 13484,13490 ****
  	ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
  				arm_ext_v6t2);
      }
!   else
      {
        /* Check that this instruction is supported for this CPU.  */
        if (!opcode->avariant ||
--- 13484,13490 ----
  	ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
  				arm_ext_v6t2);
      }
!   else if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
      {
        /* Check that this instruction is supported for this CPU.  */
        if (!opcode->avariant ||
*************** md_assemble (char *str)
*** 13517,13522 ****
--- 13517,13528 ----
  	ARM_MERGE_FEATURE_SETS (arm_arch_used, arm_arch_used,
  				*opcode->avariant);
      }
+   else
+     {
+       as_bad (_("attempt to use ARM instruction on Thumb-only core -- `%s'"),
+               str);
+       return;
+     }
    output_inst (str);
  }
  
*************** set_constant_flonums (void)
*** 18296,18301 ****
--- 18302,18317 ----
        abort ();
  }
  
+ /* Auto-select Thumb mode if it's the only available instruction set for the
+    given architecture.  */
+ 
+ static void
+ autoselect_thumb_from_cpu_variant (void)
+ {
+   if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
+     opcode_select (16);
+ }
+ 
  void
  md_begin (void)
  {
*************** md_begin (void)
*** 18396,18401 ****
--- 18412,18419 ----
  
    ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
  
+   autoselect_thumb_from_cpu_variant ();
+ 
    arm_arch_used = thumb_arch_used = arm_arch_none;
  
  #if defined OBJ_COFF || defined OBJ_ELF
Index: gas/testsuite/gas/arm/noarm.d
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.d
diff -N gas/testsuite/gas/arm/noarm.d
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.d	12 May 2006 00:12:05 -0000
***************
*** 0 ****
--- 1,3 ----
+ # name: Disallow ARM instructions on V7M
+ # as: 
+ # error-output: noarm.l
Index: gas/testsuite/gas/arm/noarm.l
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.l
diff -N gas/testsuite/gas/arm/noarm.l
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.l	12 May 2006 00:12:05 -0000
***************
*** 0 ****
--- 1,3 ----
+ [^:]*: Assembler messages:
+ [^:]*:12: Error: selected processor does not support ARM opcodes
+ [^:]*:13: Error: attempt to use ARM instruction on Thumb-only core -- `nop'
Index: gas/testsuite/gas/arm/noarm.s
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.s
diff -N gas/testsuite/gas/arm/noarm.s
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.s	12 May 2006 00:12:05 -0000
***************
*** 0 ****
--- 1,13 ----
+         .arch armv7a
+         .syntax unified
+ 	.text
+ func:
+ 	nop
+ 	movw r0, #0
+ 
+ 	.arch armv7
+ 	.thumb
+ 	nop
+ 	movw r0, #0
+ 	.arm
+ 	nop

Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Paul Brook]

On Friday 12 May 2006 01:22, Julian Brown wrote:
> +     as_bad (_("attempt to use ARM instruction on Thumb-only core --`%s'"),
> +               str); 

Other error messages talk about the "selected processor" rather than "core". 
Other than that it looks ok. Someone else will have to approve this for 
mainline.

Paul

Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Richard Earnshaw]

On Fri, 2006-05-12 at 15:54, Paul Brook wrote:
> On Friday 12 May 2006 01:22, Julian Brown wrote:
> > +     as_bad (_("attempt to use ARM instruction on Thumb-only core --`%s'"),
> > +               str); 
> 
> Other error messages talk about the "selected processor" rather than "core". 
> Other than that it looks ok. Someone else will have to approve this for 
> mainline.

I think the message should be
'attempt to use an ARM instruction on a Thumb-only processor'

ie *an* ARM, and *a* Thumb.

R.
-- 
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Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Julian Brown]

[-- Attachment #1: Type: text/plain, Size: 1123 bytes --]

Richard Earnshaw wrote:
> On Fri, 2006-05-12 at 15:54, Paul Brook wrote:
>> On Friday 12 May 2006 01:22, Julian Brown wrote:
>>> +     as_bad (_("attempt to use ARM instruction on Thumb-only core --`%s'"),
>>> +               str); 
>> Other error messages talk about the "selected processor" rather than "core". 
>> Other than that it looks ok. Someone else will have to approve this for 
>> mainline.
> 
> I think the message should be
> 'attempt to use an ARM instruction on a Thumb-only processor'
> 
> ie *an* ARM, and *a* Thumb.

Sorry, I think I forgot about this one: is this version OK for head now?

Cheers,

Julian

ChangeLog:

ChangeLog (gas):

     * config/tc-arm.c (md_assemble): Improve diagnostic when attempting
     to use ARM instructions on non-ARM-supporting cores.
     (autoselect_thumb_from_cpu_variant): New function. Switch on Thumb
     mode automatically based on cpu variant.
     (md_begin): Call above function.

ChangeLog (gas/testsuite):

     * gas/arm/noarm.s: Add test for disabled ARM insns.
     * gas/arm/noarm.d: Drive test for above.
     * gas/arm/noarm.l: Expected error output.

[-- Attachment #2: v7m-no-arm-6 --]
[-- Type: text/plain, Size: 3297 bytes --]

Index: gas/config/tc-arm.c
===================================================================
RCS file: /cvs/src/src/gas/config/tc-arm.c,v
retrieving revision 1.250.2.20
diff -c -p -r1.250.2.20 tc-arm.c
*** gas/config/tc-arm.c	19 Jul 2006 13:08:20 -0000	1.250.2.20
--- gas/config/tc-arm.c	19 Jul 2006 20:29:55 -0000
*************** md_assemble (char *str)
*** 13729,13735 ****
  	ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
  				arm_ext_v6t2);
      }
!   else
      {
        /* Check that this instruction is supported for this CPU.  */
        if (!opcode->avariant ||
--- 13729,13735 ----
  	ARM_MERGE_FEATURE_SETS (thumb_arch_used, thumb_arch_used,
  				arm_ext_v6t2);
      }
!   else if (ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
      {
        /* Check that this instruction is supported for this CPU.  */
        if (!opcode->avariant ||
*************** md_assemble (char *str)
*** 13762,13767 ****
--- 13762,13773 ----
  	ARM_MERGE_FEATURE_SETS (arm_arch_used, arm_arch_used,
  				*opcode->avariant);
      }
+   else
+     {
+       as_bad (_("attempt to use an ARM instruction on a Thumb-only processor "
+ 		"-- `%s'"), str);
+       return;
+     }
    output_inst (str);
  }
  
*************** set_constant_flonums (void)
*** 18766,18771 ****
--- 18772,18787 ----
        abort ();
  }
  
+ /* Auto-select Thumb mode if it's the only available instruction set for the
+    given architecture.  */
+ 
+ static void
+ autoselect_thumb_from_cpu_variant (void)
+ {
+   if (!ARM_CPU_HAS_FEATURE (cpu_variant, arm_ext_v1))
+     opcode_select (16);
+ }
+ 
  void
  md_begin (void)
  {
*************** md_begin (void)
*** 18866,18871 ****
--- 18882,18889 ----
  
    ARM_MERGE_FEATURE_SETS (cpu_variant, *mcpu_cpu_opt, *mfpu_opt);
  
+   autoselect_thumb_from_cpu_variant ();
+ 
    arm_arch_used = thumb_arch_used = arm_arch_none;
  
  #if defined OBJ_COFF || defined OBJ_ELF
Index: gas/testsuite/gas/arm/noarm.d
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.d
diff -N gas/testsuite/gas/arm/noarm.d
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.d	19 Jul 2006 20:29:55 -0000
***************
*** 0 ****
--- 1,3 ----
+ # name: Disallow ARM instructions on V7M
+ # as: 
+ # error-output: noarm.l
Index: gas/testsuite/gas/arm/noarm.l
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.l
diff -N gas/testsuite/gas/arm/noarm.l
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.l	19 Jul 2006 20:29:55 -0000
***************
*** 0 ****
--- 1,3 ----
+ [^:]*: Assembler messages:
+ [^:]*:12: Error: selected processor does not support ARM opcodes
+ [^:]*:13: Error: attempt to use an ARM instruction on a Thumb-only processor -- `nop'
Index: gas/testsuite/gas/arm/noarm.s
===================================================================
RCS file: gas/testsuite/gas/arm/noarm.s
diff -N gas/testsuite/gas/arm/noarm.s
*** /dev/null	1 Jan 1970 00:00:00 -0000
--- gas/testsuite/gas/arm/noarm.s	19 Jul 2006 20:29:55 -0000
***************
*** 0 ****
--- 1,13 ----
+         .arch armv7a
+         .syntax unified
+ 	.text
+ func:
+ 	nop
+ 	movw r0, #0
+ 
+ 	.arch armv7
+ 	.thumb
+ 	nop
+ 	movw r0, #0
+ 	.arm
+ 	nop

Re: [PATCH, ARM]: Fix diagnostics & disallow ARM instructions on V7M cores

[Nick Clifton]

Hi Julian,

> ChangeLog (gas):
> 
>     * config/tc-arm.c (md_assemble): Improve diagnostic when attempting
>     to use ARM instructions on non-ARM-supporting cores.
>     (autoselect_thumb_from_cpu_variant): New function. Switch on Thumb
>     mode automatically based on cpu variant.
>     (md_begin): Call above function.
> 
> ChangeLog (gas/testsuite):
> 
>     * gas/arm/noarm.s: Add test for disabled ARM insns.
>     * gas/arm/noarm.d: Drive test for above.
>     * gas/arm/noarm.l: Expected error output.
> 

Approved - please apply.

Cheers
   Nick