Re: [PATCH][Binutils][GAS] arm: Add cfi expression support for ra_auth_code

[Richard Earnshaw <Richard.Earnshaw@foss.arm.com>]

On 18/07/2022 17:01, Victor Do Nascimento via Binutils wrote:
> Hi all,
> 
> This patch extends assembler support for the use of ra_auth_code register,
> particularly in the context of CFI directives, mapping the register to
> the correct DWARF-2 register number.
> 
> Tested for arm-none-eabi.
> 
> Thanks,
> Victor.
> 
> gas/Changelog:
> 
>      * gas/config/tc-arm.c (tc_arm_regname_to_dw2regnum): Add
>      REG_TYPE_PSEUDO handling.
>      * gas/testsuite/gas/arm/cfi-pacbti-m-readelf.d: New.
>      * gas/testsuite/gas/arm/cfi-pacbti-m.s: New.
> ---
>   gas/config/tc-arm.c                          |  9 ++++++
>   gas/testsuite/gas/arm/cfi-pacbti-m-readelf.d | 31 ++++++++++++++++++++
>   gas/testsuite/gas/arm/cfi-pacbti-m.s         | 22 ++++++++++++++
>   3 files changed, 62 insertions(+)
>   create mode 100644 gas/testsuite/gas/arm/cfi-pacbti-m-readelf.d
>   create mode 100644 gas/testsuite/gas/arm/cfi-pacbti-m.s
> 
> diff --git a/gas/config/tc-arm.c b/gas/config/tc-arm.c
> index 2e6d175482e..bf912ccf2d5 100644
> --- a/gas/config/tc-arm.c
> +++ b/gas/config/tc-arm.c
> @@ -27933,6 +27933,15 @@ tc_arm_regname_to_dw2regnum (char *regname)
>     if (reg != FAIL)
>       return reg + 256;
>   
> +  reg = arm_reg_parse (&regname, REG_TYPE_PSEUDO);
> +  switch (reg)
> +  {
> +    case 12:
> +      return 143;

Sorry, this doesn't look right.  The comment where the pseudos are 
defined says:

   /* DWARF ABI defines RA_AUTH_CODE to 143. It also reserves 134-142 
for future
      expansion.  RA_AUTH_CODE here is given the value 143 % 134 to make 
it easy
      for tc_arm_regname_to_dw2regnum to translate to DWARF reg number using
      134 + reg_number should the range 134 to 142 be used for more 
pseudo regs
      in the future.  This also helps fit RA_AUTH_CODE into a bitmask.  */

though I'll note that 143 % 134 is 9, not 12.

So really, the code here should be adding back the base for the range 
that it covers rather than just handling a special case.

And, of course, either the comment needs fixing, or the assigned 
internal number needs fixing.

R.

> +    default:
> +      break;
> +  }
> +
>     return FAIL;
>   }
>   
> diff --git a/gas/testsuite/gas/arm/cfi-pacbti-m-readelf.d b/gas/testsuite/gas/arm/cfi-pacbti-m-readelf.d
> new file mode 100644
> index 00000000000..997ea75f179
> --- /dev/null
> +++ b/gas/testsuite/gas/arm/cfi-pacbti-m-readelf.d
> @@ -0,0 +1,31 @@
> +#readelf: -wf
> +#source: cfi-pacbti-m.s
> +#name: Call Frame information for Armv8.1-M.Mainline PACBTI extension
> +# This test is only valid on ELF based ports.
> +#notarget: *-*-pe *-*-wince
> +# VxWorks needs a special variant of this file.
> +#skip: *-*-vxworks*
> +
> +Contents of the .eh_frame section:
> +
> +
> +00000000 00000010 00000000 CIE
> +  Version:               1
> +  Augmentation:          "zR"
> +  Code alignment factor: 2
> +  Data alignment factor: -4
> +  Return address column: 14
> +  Augmentation data:     1b
> +  DW_CFA_def_cfa: r13 ofs 0
> +
> +00000014 00000020 00000018 FDE cie=00000000 pc=00000000..0000000c
> +  DW_CFA_advance_loc: 4 to 00000004
> +  DW_CFA_register: r143 in r12
> +  DW_CFA_advance_loc: 4 to 00000008
> +  DW_CFA_def_cfa_offset: 8
> +  DW_CFA_offset: r14 at cfa-8
> +  DW_CFA_offset: r12 at cfa-4
> +  DW_CFA_advance_loc: 4 to 0000000c
> +  DW_CFA_restore_extended: r143
> +  DW_CFA_restore: r14
> +  DW_CFA_def_cfa_offset: 0
> diff --git a/gas/testsuite/gas/arm/cfi-pacbti-m.s b/gas/testsuite/gas/arm/cfi-pacbti-m.s
> new file mode 100644
> index 00000000000..515400d86f5
> --- /dev/null
> +++ b/gas/testsuite/gas/arm/cfi-pacbti-m.s
> @@ -0,0 +1,22 @@
> +    .arch armv8.1-m.main
> +    .arch_extension pacbti
> +    .eabi_attribute Tag_PAC_extension, 2
> +    .eabi_attribute Tag_BTI_extension, 2
> +    .eabi_attribute Tag_BTI_use, 1
> +    .eabi_attribute Tag_PACRET_use, 1
> +    .syntax unified
> +    .text
> +    .thumb
> +.Lstart:
> +    .cfi_startproc
> +    pacbti ip, lr, sp
> +    .cfi_register ra_auth_code, ip
> +    push {ip, lr}
> +    .cfi_def_cfa_offset 8
> +    .cfi_offset lr, -8
> +    .cfi_offset ip, -4
> +    pop {ip, lr}
> +    .cfi_restore 143
> +    .cfi_restore 14
> +    .cfi_def_cfa_offset 0
> +    .cfi_endproc