Re: [ARM/FDPIC v5 08/21] [ARM] FDPIC: Enforce local/global binding for function descriptors

[Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>]

Hi Christophe,

On 5/15/19 1:39 PM, Christophe Lyon wrote:
> Use local binding rules to decide whether we can use GOTOFFFUNCDESC to
> compute the function address.
>
> 2019-XX-XX  Christophe Lyon  <christophe.lyon@st.com>
>         Mickaël Guêné <mickael.guene@st.com>
>
>         gcc/
>         * config/arm/arm.c (arm_local_funcdesc_p): New function.
>         (legitimize_pic_address): Enforce binding rules on function
>         pointers in FDPIC mode.
>         (arm_assemble_integer): Likewise.
>
> Change-Id: I3fa0b63bc0f672903f405aa72cc46052de1c0feb
>
> diff --git a/gcc/config/arm/arm.c b/gcc/config/arm/arm.c
> index dbd1671..40e3f3b 100644
> --- a/gcc/config/arm/arm.c
> +++ b/gcc/config/arm/arm.c
> @@ -3790,6 +3790,42 @@ arm_options_perform_arch_sanity_checks (void)
>      }
>  }
>
> +/* Test whether a local function descriptor is canonical, i.e.,
> +   whether we can use GOTOFFFUNCDESC to compute the address of the
> +   function.  */
> +static bool
> +arm_fdpic_local_funcdesc_p (rtx fnx)
> +{
> +  tree fn;
> +  enum symbol_visibility vis;
> +  bool ret;
> +
> +  if (!TARGET_FDPIC)
> +    return TRUE;
> +
> +  if (! SYMBOL_REF_LOCAL_P (fnx))
> +    return FALSE;
> +

Please use normal C 'true' and 'false' in this patch.

Ok with that change once the rest is approved.

Thanks,

Kyrill


> +  fn = SYMBOL_REF_DECL (fnx);
> +
> +  if (! fn)
> +    return FALSE;
> +
> +  vis = DECL_VISIBILITY (fn);
> +
> +  if (vis == VISIBILITY_PROTECTED)
> +    /* Private function descriptors for protected functions are not
> +       canonical.  Temporarily change the visibility to global so that
> +       we can ensure uniqueness of funcdesc pointers.  */
> +    DECL_VISIBILITY (fn) = VISIBILITY_DEFAULT;
> +
> +  ret = default_binds_local_p_1 (fn, flag_pic);
> +
> +  DECL_VISIBILITY (fn) = vis;
> +
> +  return ret;
> +}
> +
>  static void
>  arm_add_gc_roots (void)
>  {
> @@ -7563,7 +7599,9 @@ legitimize_pic_address (rtx orig, machine_mode 
> mode, rtx reg, rtx pic_reg,
>             || (GET_CODE (orig) == SYMBOL_REF
>                 && SYMBOL_REF_LOCAL_P (orig)
>                 && (SYMBOL_REF_DECL (orig)
> -                  ? !DECL_WEAK (SYMBOL_REF_DECL (orig)) : 1)))
> +                  ? !DECL_WEAK (SYMBOL_REF_DECL (orig)) : 1)
> +              && (!SYMBOL_REF_FUNCTION_P (orig)
> +                  || arm_fdpic_local_funcdesc_p (orig))))
>            && NEED_GOT_RELOC
>            && arm_pic_data_is_text_relative)
>          insn = arm_pic_static_addr (orig, reg);
> @@ -23231,7 +23269,9 @@ arm_assemble_integer (rtx x, unsigned int 
> size, int aligned_p)
>                || (GET_CODE (x) == SYMBOL_REF
>                    && (!SYMBOL_REF_LOCAL_P (x)
>                        || (SYMBOL_REF_DECL (x)
> -                         ? DECL_WEAK (SYMBOL_REF_DECL (x)) : 0))))
> +                         ? DECL_WEAK (SYMBOL_REF_DECL (x)) : 0)
> +                     || (SYMBOL_REF_FUNCTION_P (x)
> +                         && !arm_fdpic_local_funcdesc_p (x)))))
>              {
>                if (TARGET_FDPIC && SYMBOL_REF_FUNCTION_P (x))
>                  fputs ("(GOTFUNCDESC)", asm_out_file);
> -- 
> 2.6.3
>