[PATCH v2 2/2] Enable arch-specific CFI directives and DWARF instructions only when required by the target (part 1)

[Jan Beulich]

On 25.04.2025 13:04, Matthieu Longo wrote:
> --- a/gas/dw2gencfi.c
> +++ b/gas/dw2gencfi.c
> @@ -720,9 +720,16 @@ const pseudo_typeS cfi_pseudo_table[] =
>      { "cfi_same_value", dot_cfi, DW_CFA_same_value },
>      { "cfi_remember_state", dot_cfi, DW_CFA_remember_state },
>      { "cfi_restore_state", dot_cfi, DW_CFA_restore_state },
> -    { "cfi_window_save", dot_cfi, DW_CFA_GNU_window_save },
> +#if TC_AARCH64
> +    /* cfi_window_save is an alias of cfi_negate_ra_state which is kept for
> +       backward-compatibility concerns.  */
> +    { "cfi_window_save", dot_cfi, DW_CFA_AARCH64_negate_ra_state },

Why's this of concern only for Arm64?

> --- a/gas/gen-sframe.c
> +++ b/gas/gen-sframe.c
> @@ -1257,6 +1257,8 @@ sframe_xlate_do_restore (struct sframe_xlate_ctx *xlate_ctx,
>    return SFRAME_XLATE_OK;
>  }
>  
> +#if TC_AARCH64
> +
>  /* Translate DW_CFA_AARCH64_negate_ra_state into SFrame context.
>     Return SFRAME_XLATE_OK if success.  */
>  
> @@ -1287,30 +1289,7 @@ sframe_xlate_do_aarch64_negate_ra_state_with_pc (struct sframe_xlate_ctx *xlate_
>    return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
>  }
>  
> -/* Translate DW_CFA_GNU_window_save into SFrame context.
> -   DW_CFA_GNU_window_save is a DWARF Sparc extension, but is multiplexed with a
> -   directive of DWARF AArch64 extension: DW_CFA_AARCH64_negate_ra_state.
> -   The AArch64 backend of GCC 14 and older versions was emitting mistakenly the
> -   Sparc CFI directive (.cfi_window_save).  From GCC 15, the AArch64 backend
> -   only emits .cfi_negate_ra_state.  For backward compatibility, the handler for
> -   .cfi_window_save needs to check whether the directive was used in a AArch64
> -   ABI context or not.
> -   Return SFRAME_XLATE_OK if success.  */
> -
> -static int
> -sframe_xlate_do_gnu_window_save (struct sframe_xlate_ctx *xlate_ctx,
> -				 struct cfi_insn_data *cfi_insn)
> -{
> -  unsigned char abi_arch = sframe_get_abi_arch ();
> -
> -  /* Translate DW_CFA_AARCH64_negate_ra_state into SFrame context.  */
> -  if (abi_arch == SFRAME_ABI_AARCH64_ENDIAN_BIG
> -      || abi_arch == SFRAME_ABI_AARCH64_ENDIAN_LITTLE)
> -    return sframe_xlate_do_aarch64_negate_ra_state (xlate_ctx, cfi_insn);
> -
> -  as_warn (_("skipping SFrame FDE; .cfi_window_save"));
> -  return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
> -}
> +#endif /* TC_AARCH64 */
>  
>  /* Handle DW_CFA_expression in .cfi_escape.
>  
> @@ -1622,14 +1601,14 @@ sframe_do_cfi_insn (struct sframe_xlate_ctx *xlate_ctx,
>      case DW_CFA_restore:
>        err = sframe_xlate_do_restore (xlate_ctx, cfi_insn);
>        break;
> -    /* DW_CFA_AARCH64_negate_ra_state is multiplexed with
> -       DW_CFA_GNU_window_save.  */
> -    case DW_CFA_GNU_window_save:
> -      err = sframe_xlate_do_gnu_window_save (xlate_ctx, cfi_insn);
> +#if TC_AARCH64
> +    case DW_CFA_AARCH64_negate_ra_state:
> +      err = sframe_xlate_do_aarch64_negate_ra_state (xlate_ctx, cfi_insn);
>        break;
>      case DW_CFA_AARCH64_negate_ra_state_with_pc:
>        err = sframe_xlate_do_aarch64_negate_ra_state_with_pc (xlate_ctx, cfi_insn);
>        break;
> +#endif /* TC_AARCH64 */
>      case DW_CFA_register:
>        err = sframe_xlate_do_register (xlate_ctx, cfi_insn);
>        break;

This wants looking over by Indu (now Cc-ed).

Jan