Re: [PATCH, BINUTILS, AARCH64, 7/9] Add BTI instruction

["Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>]

On 19/09/18 15:29, Sudakshina Das wrote:
> Hi
> 
> This patch is part of the patch series to add support for ARMv8.5-A
> extensions.
> (https://developer.arm.com/products/architecture/cpu-architecture/a-profile/docs/ddi0596/a/a64-base-instructions-alphabetic-order/bti-branch-target-identification)
> 
> The Branch Target Identification instructions (BTI) are allocated to
> existing HINT space, using HINT numbers 32, 34, 36, 38, such that
> bits[7:6] of the instruction identify the compatibility of the BTI
> instruction to different branches.
>         BTI {<targets>}
> where <targets> one of the following, specifying which type of
> indirection is allowed:
>        j : Can be a target of any BR Xn isntruction.
>        c : Can be a target of any BLR Xn and BR {X16|X17}.
>        jc: Can be a target of any free branch.
> 
> A BTI instruction without any <targets> is the strictest of all and
> can not be a target of nay free branch.
> 
> Testing done: Builds and reg tests all pass on aarch64-none-linux-gnu.
> and aarch64-none-elf. Updated and added new tests to check.
> 
> Ok for trunk?
> 
> Thanks
> Sudi
> PS. I do not have commit access so if OK can someone apply for me?
> Also the patch was too big to attach due to the regenerated files.
> 
> 
> *** include/ChangeLog ***
> 
> 2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>
> 
> 	* opcode/aarch64.h (AARCH64_FEATURE_BTI): New.
> 	(AARCH64_ARCH_V8_5): Add AARCH64_FEATURE_BTI by default.
> 	(aarch64_opnd): Add AARCH64_OPND_BTI_TARGET.
> 
> *** opcodes/ChangeLog ***
> 
> 2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>
> 
> 	* aarch64-opc.c (aarch64_hint_options): New entries for
> 	c, j, jc and default for BTI.
> 	(aarch64_print_operand): Add case for AARCH64_OPND_BTI_TARGET
> 	and create an exception for "default" option.
> 	* aarch64-tbl.h (aarch64_feature_bti, BTI, BTI_INSN): New.
> 	(aarch64_opcode_table): Add entry for BTI.
> 	(AARCH64_OPERANDS): Add new description for BTI targets.
> 	* aarch64-asm-2.c: Regenerate.
> 	* aarch64-dis-2.c: Regenerate.
> 	* aarch64-opc-2.c: Regenerate.
> 
> *** gas/ChangeLog ***
> 
> 2018-xx-xx  Sudakshina Das  <sudi.das@arm.com>
> 
> 	* config/tc-aarch64.c (parse_bti_operand): New.
> 	(process_omitted_operand): Add case for AARCH64_OPND_BTI_TARGET.
> 	(parse_operands): Likewise.
> 	* testsuite/gas/aarch64/system.d: Update for BTI.
> 	* testsuite/gas/aarch64/bti.s: New.
> 	* testsuite/gas/aarch64/bti.d: New.
> 	* testsuite/gas/aarch64/illegal-bti.d: New.
> 	* testsuite/gas/aarch64/illegal-bti.l: New.
> 
> 
> 

gas/config/tc-aarch64.c:

+    case 0x22:
+    case 0x24:
+    case 0x26: break;
+    default:

Put the 'break on a separate line when you have multiple cases.  Blank
line before the default.

Also, if the user writes

	bti default
	bti fred

they will get a different error message for each line.  That's inconsistent.

opcodes/aarch64-opc.c:

     case AARCH64_OPND_BARRIER_PSB:
-      snprintf (buf, size, "%s", opnd->hint_option->name);
+    case AARCH64_OPND_BTI_TARGET:
+      /* BTI with no target.  */
+      if (opnd->hint_option->value != 0x20)
+	snprintf (buf, size, "%s", opnd->hint_option->name);
       break;

I don't particularly like the specific exception here.  Can we find a
better way to do this?  Perhaps a flag bit associated with the tupple to
indicate that the name field should not be printed.