Re: [PATCH] LoongArch: Update comment about bottom bit usage in TLS GOT construction

[mengqinggang <mengqinggang@loongson.cn>]

At the beginning of implementation, we try to IE and GD only generate 
their own GOT entry,
so we need two bits to do the flags.


在 2023/12/28 下午10:58, Tatsuyuki Ishi 写道:
> The GOT assignment logic, likely copied from another backend, does not in
> fact require multiple flags to construct multiple type of slots. Instead,
> all slots are initialized on the first relocation encountered. Update
> comment to avoid confusion.
> ---
>   bfd/elfnn-loongarch.c | 17 +++++++----------
>   1 file changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
> index 64c34e99261..d66dcee1100 100644
> --- a/bfd/elfnn-loongarch.c
> +++ b/bfd/elfnn-loongarch.c
> @@ -3656,16 +3656,13 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
>   	  relocation -= elf_hash_table (info)->tls_sec->vma;
>   	  break;
>   
> -	/* TLS IE LD/GD process separately is troublesome.
> -	   When a symbol is both ie and LD/GD, h->got.off |= 1
> -	   make only one type be relocated.  We must use
> -	   h->got.offset |= 1 and h->got.offset |= 2
> -	   diff IE and LD/GD.  And all (got_off & (~(bfd_vma)1))
> -	   (IE LD/GD and reusable GOT reloc) must change to
> -	   (got_off & (~(bfd_vma)3)), beause we use lowest 2 bits
> -	   as a tag.
> -	   Now, LD and GD is both GOT_TLS_GD type, LD seems to
> -	   can be omitted.  */
> +	/* The bottom bit of h->got.offset is (ab)used as a flag.
> +	   Upon encountering the first TLS relocation, we initialize all GOT
> +	   slots for the corresponding symbol and set the bottom bit to 1.
> +
> +	   The second and subsequent relocations will check the flag, see that
> +	   the slot is already initialized, and move on to just relocating the
> +	   entry.  */
>   	case R_LARCH_TLS_IE_PC_HI20:
>   	case R_LARCH_TLS_IE_HI20:
>   	case R_LARCH_TLS_LD_PC_HI20: