On Tue, Jan 31, 2023 at 11:38:59PM -0800, Fangrui Song via Gcc-patches wrote:
> Follow aarch64 and riscv ports by using (global ? DW_EH_PE_indirect : 0)
> | DW_EH_PE_pcrel for -fno-pic code. This avoids a canonical PLT entry
> for a personality reference in .eh_frame and a copy relocation for a
> typeinfo reference in .gcc_except_table, when the definition is in
> libstdc++.so.6.
>
> gcc/
>
> PR target/108622
> * config/i386/i386.cc (asm_preferred_eh_data_format): Always use the
> PIC encoding. Use DW_EH_PE_indirect if global.
Not a review, just comments:
> diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
> index 3cacf738c4a..b572dd46a62 100644
> --- a/gcc/config/i386/i386.cc
> +++ b/gcc/config/i386/i386.cc
> @@ -22851,22 +22851,13 @@ ix86_stack_protect_fail (void)
> int
> asm_preferred_eh_data_format (int code, int global)
> {
> - /* PE-COFF is effectively always -fPIC because of the .reloc section. */
> - if (flag_pic || TARGET_PECOFF || !ix86_direct_extern_access)
> - {
> - int type = DW_EH_PE_sdata8;
> - if (ptr_mode == SImode
> - || ix86_cmodel == CM_SMALL_PIC
> - || (ix86_cmodel == CM_MEDIUM_PIC && (global || code)))
> - type = DW_EH_PE_sdata4;
> - return (global ? DW_EH_PE_indirect : 0) | DW_EH_PE_pcrel | type;
> - }
> -
> - if (ix86_cmodel == CM_SMALL
> - || (ix86_cmodel == CM_MEDIUM && code))
> - return DW_EH_PE_udata4;
> -
> - return DW_EH_PE_absptr;
> + int type = DW_EH_PE_sdata8;
> + if (ptr_mode == SImode || ix86_cmodel == CM_SMALL ||
> + ix86_cmodel == CM_SMALL_PIC ||
> + (ix86_cmodel == CM_MEDIUM && code) ||
> + (ix86_cmodel == CM_MEDIUM_PIC && (global || code)))
The above is incorrectly formatted, the GCC Coding Conventions
say || etc. shouldn't be at the end of lines, but rather at the
start of the next ones.
And, while I can understand the rationale for global cases
(though am not sure I agree, as currently the user can choose
by using -mno-direct-extern-access or not using it, the above change
disallows the choice), for !global I miss the point altogether.
In non-PIC (and non-PECOFF maybe, don't know that format well)
code if code references a local symbol, it will never generate
a copy relocation and so DW_EH_PE_udata4 could be just fine and cheaper
to handle on the consumer sides.
Jakub
