On Wed, Jan 12, 2022 at 7:22 AM HAO CHEN GUI <guih...@linux.ibm.com> wrote:
>
> Hi,
> This patch enables absolute jump table by default on rs6000. The relative
> jump tables are used when
> it's explicit set by "rs6000_relative_jumptables",
> or jump tables are placed in text section but global relocation is
> required.
>
> Bootstrapped and tested on powerpc64-linux BE and LE with no regressions.
> Is this okay for trunk?
> Any recommendations? Thanks a lot.
>
> ChangeLog
> 2022-01-12 Haochen Gui <guih...@linux.ibm.com>
>
> gcc/
> * config/rs6000/linux64.h (JUMP_TABLES_IN_TEXT_SECTION): Define.
> * config/rs6000/rs6000.c (rs6000_gen_pic_addr_diff_vec): Return
> true when relative jump table is explicit required or jump tables have
> to be put in text section but global relocation is also required.
> * config/rs6000/rs6000.opt (rs6000_relative_jumptables): Disable.
>
> patch.diff
> diff --git a/gcc/config/rs6000/linux64.h b/gcc/config/rs6000/linux64.h
> index d617f346f81..2e257c60f8c 100644
> --- a/gcc/config/rs6000/linux64.h
> +++ b/gcc/config/rs6000/linux64.h
> @@ -239,7 +239,7 @@ extern int dot_symbols;
>
> /* Indicate that jump tables go in the text section. */
> #undef JUMP_TABLES_IN_TEXT_SECTION
> -#define JUMP_TABLES_IN_TEXT_SECTION TARGET_64BIT
> +#define JUMP_TABLES_IN_TEXT_SECTION 0
>
> /* The linux ppc64 ABI isn't explicit on whether aggregates smaller
> than a doubleword should be padded upward or downward. You could
> diff --git a/gcc/config/rs6000/rs6000.c b/gcc/config/rs6000/rs6000.c
> index 319182e94d9..9fba893a27a 100644
> --- a/gcc/config/rs6000/rs6000.c
> +++ b/gcc/config/rs6000/rs6000.c
> @@ -28465,7 +28465,9 @@ rs6000_emit_xxspltidp_v2df (rtx dst, long value)
> static bool
> rs6000_gen_pic_addr_diff_vec (void)
> {
> - return rs6000_relative_jumptables;
> + return rs6000_relative_jumptables
> + || (JUMP_TABLES_IN_TEXT_SECTION
> + && targetm.asm_out.reloc_rw_mask () == 3);
> }
This seems like contorted logic and overriding the
rs6000_relative_jumptables option change. The later part of the patch
overrides rs6000_relative_jumptables for all rs6000 configurations,
and then changes this one use of rs6000_relative_jumptables to add
more logic to revert to the old meaning for some targets.
What about all of the other uses of rs6000_relative_jumptables in the
target? What about rs6000.md?
I highly doubt that this patch is correct.
Why not override rs6000_relative_jumptables for PPC64 Linux instead of
changing its value globally and then trying to fix it up?
Thanks, David
>
> void
> diff --git a/gcc/config/rs6000/rs6000.opt b/gcc/config/rs6000/rs6000.opt
> index c2a77182a9e..75e3fa86829 100644
> --- a/gcc/config/rs6000/rs6000.opt
> +++ b/gcc/config/rs6000/rs6000.opt
> @@ -630,7 +630,7 @@ Target Mask(MMA) Var(rs6000_isa_flags)
> Generate (do not generate) MMA instructions.
>
> mrelative-jumptables
> -Target Undocumented Var(rs6000_relative_jumptables) Init(1) Save
> +Target Undocumented Var(rs6000_relative_jumptables) Init(0) Save
>
> mrop-protect
> Target Var(rs6000_rop_protect) Init(0)
