[PATCH, GCC, AARCH64] Add GNU note section with BTI and PAC.

[Sudakshina Das]

Hi Richard

Thanks for the comments and pointing out the much cleaner existing asm 
output functions!

On 29/03/2019 17:51, Richard Henderson wrote:
>> +#define ASM_LONG "\t.long\t"
> 
> Do not replicate targetm.asm_out.aligned_op.si, or integer_asm_op, really.
> 
>> +aarch64_file_end_indicate_exec_stack ()
>> +{
>> +  file_end_indicate_exec_stack ();
>> +
>> +  if (!aarch64_bti_enabled ()
>> +      && aarch64_ra_sign_scope == AARCH64_FUNCTION_NONE)
>> +    {
>> +      return;
>> +    }
> 
> This is redundant with...
> 
>> +
>> +  unsigned feature_1_and = 0;
>> +  if (aarch64_bti_enabled ())
>> +    feature_1_and |= GNU_PROPERTY_AARCH64_FEATURE_1_BTI;
>> +
>> +  if (aarch64_ra_sign_scope != AARCH64_FUNCTION_NONE)
>> +    feature_1_and |= GNU_PROPERTY_AARCH64_FEATURE_1_PAC;
>> +
>> +  if (feature_1_and)
> 
> ... this.  I prefer the second, as it's obvious.
> 
>> +      ASM_OUTPUT_ALIGN (asm_out_file, p2align);
>> +      /* name length.  */
>> +      fprintf (asm_out_file, ASM_LONG " 1f - 0f\n");
>> +      /* data length.  */
>> +      fprintf (asm_out_file, ASM_LONG " 4f - 1f\n");
>> +      /* note type: NT_GNU_PROPERTY_TYPE_0.  */
>> +      fprintf (asm_out_file, ASM_LONG " 5\n");
>> +      fprintf (asm_out_file, "0:\n");
>> +      /* vendor name: "GNU".  */
>> +      fprintf (asm_out_file, STRING_ASM_OP " \"GNU\"\n");
>> +      fprintf (asm_out_file, "1:\n");
>> +      ASM_OUTPUT_ALIGN (asm_out_file, p2align);
>> +      /* pr_type: GNU_PROPERTY_AARCH64_FEATURE_1_AND.  */
>> +      fprintf (asm_out_file, ASM_LONG " 0x%x\n",
>> +	       GNU_PROPERTY_AARCH64_FEATURE_1_AND);
>> +      /* pr_datasz.  */\
>> +      fprintf (asm_out_file, ASM_LONG " 3f - 2f\n");
>> +      fprintf (asm_out_file, "2:\n");
>> +      /* GNU_PROPERTY_AARCH64_FEATURE_1_XXX.  */
>> +      fprintf (asm_out_file, ASM_LONG " 0x%x\n", feature_1_and);
>> +      fprintf (asm_out_file, "3:\n");
>> +      ASM_OUTPUT_ALIGN (asm_out_file, p2align);
>> +      fprintf (asm_out_file, "4:\n");
> 
> This could stand to use a comment, a moment's thinking about the sizes, and to
> use the existing asm output functions.
> 
> 	/* PT_NOTE header: namesz, descsz, type.
> 	   namesz = 4 ("GNU\0")
> 	   descsz = 12 (see below)

I was trying out these changes but the descsz of 12 gets rejected by 
readelf. It hits the following

   unsigned int    size = is_32bit_elf ? 4 : 8;

   printf (_("      Properties: "));

   if (pnote->descsz < 8 || (pnote->descsz % size) != 0)
     {
       printf (_("<corrupt GNU_PROPERTY_TYPE, size = %#lx>\n"), 
pnote->descsz);
       return;
     }

Thanks
Sudi

> 	   type   = 5 (NT_GNU_PROPERTY_TYPE_0).  */
> 	assemble_align (POINTER_SIZE);
> 	assemble_integer (GEN_INT (4), 4, 32, 1);
> 	assemble_integer (GEN_INT (12), 4, 32, 1);
> 	assemble_integer (GEN_INT (5), 4, 32, 1);
> 
> 	/* PT_NOTE name */
> 	assemble_string ("GNU", 4);
> 
> 	/* PT_NOTE contents for NT_GNU_PROPERTY_TYPE_0:
> 	   type   = 0xc0000000 (GNU_PROPERTY_AARCH64_FEATURE_1_AND),
>             datasz = 4
>             data   = feature_1_and
>             Note that the current section offset is 16,
>             and there has been no padding so far.  */
> 	assemble_integer (GEN_INT (0xc0000000), 4, 32, 1);
> 	assemble_integer (GEN_INT (4), 4, 32, 1);
> 	assemble_integer (GEN_INT (feature_1_and), 4, 32, 1);
> 
> 	/* Pad the size of the note to the required alignment. */
> 	assemble_align (POINTER_SIZE);
> 
> 
> r~
>