Re: [PATCH] LoongArch: Disallow TLS transition when a section contains TLS_IE64 or TLS_DESC64 reloc

[mengqinggang <mengqinggang@loongson.cn>]

Hi,

For TLS transition, we want to change to that the instructions that can be
converted must have a R_LARCH_RELAX relocation.

After 32ee2b4b71c78d3dc0c0b1f87f25fe5df8786b71 commit, the gas not
emit R_LARCH_RELAX for two register macros.


在 2024/1/25 下午9:36, Xi Ruoyao 写道:
> We cannot do TLS transition for them without a psABI revision marking
> some "key" instructions with reloc.  Disallow the transition when we see
> such a reloc in a section to prevent an invalid "partial" transition.
>
> Signed-off-by: Xi Ruoyao <xry111@xry111.site>
> ---
>
> To Nick:
>
> Sorry for another late update, but we need this for 2.42 or anything
> compiled with -mcmodel=extreme and using errno will just blow up :(.
>
>   bfd/elfnn-loongarch.c                         | 53 +++++++++++++++++--
>   .../ld-loongarch-elf/ld-loongarch-elf.exp     | 14 +++++
>   .../ld-loongarch-elf/tls-ie64-notrans.d       |  3 ++
>   .../ld-loongarch-elf/tls-ie64-notrans.s       |  7 +++
>   4 files changed, 73 insertions(+), 4 deletions(-)
>   create mode 100644 ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d
>   create mode 100644 ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s
>
> diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
> index b62bb424644..b9709401f56 100644
> --- a/bfd/elfnn-loongarch.c
> +++ b/bfd/elfnn-loongarch.c
> @@ -717,6 +717,40 @@ loongarch_tls_transition (struct bfd_link_info *info, unsigned int r_type,
>     return loongarch_tls_transition_without_check (info, r_type, h);
>   }
>   
> +/* For TLS IE in extreme code model:
> +       pcalau12i t0, %ie_pc_hi20(x)
> +       li.d      t1, %ie_pc_lo12(x)
> +       lu32i.d   t1, %ie64_pc_lo20(x)
> +       lu52i.d   t1, t1, %ie64_pc_hi12(x)
> +       ldx.d     t0, t0, t1
> +   We've no idea how to remove the ldx.d instruction or turn it into a
> +   nop because there is no reloc on it.  But we have to stop turning this
> +   into LE or we'll end up
> +       lu12i.w   t0, %le_hi20(x)
> +       ori       t1, t1, %le_lo12(x)
> +       lu32i.d   t1, %ie64_pc_lo20(x)
> +       lu52i.d   t1, t1, %ie64_pc_hi12(x)
> +       ldx.d     t0, t0, t1
> +   which is completely wrong.  For TLS DESC it's similar: we cannot remove
> +   the add.d instruction but we have to stop the transition.  */
> +static bool
> +loongarch_elf_allow_tls_transition_p (const Elf_Internal_Rela *r_begin,
> +				      const Elf_Internal_Rela *r_end)
> +{
> +  for (; r_begin != r_end; r_begin++)
> +    switch (ELFNN_R_TYPE (r_begin->r_info))
> +      {
> +      case R_LARCH_TLS_IE64_PC_HI12:
> +      case R_LARCH_TLS_IE64_PC_LO20:
> +      case R_LARCH_TLS_DESC64_PC_HI12:
> +      case R_LARCH_TLS_DESC64_PC_LO20:
> +	return false;
> +      }
> +
> +  return true;
> +}
> +
> +
>   /* Look through the relocs for a section during the first phase, and
>      allocate space in the global offset table or procedure linkage
>      table.  */
> @@ -730,6 +764,7 @@ loongarch_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
>     struct elf_link_hash_entry **sym_hashes;
>     const Elf_Internal_Rela *rel;
>     asection *sreloc = NULL;
> +  bool allow_tls_transition;
>   
>     if (bfd_link_relocatable (info))
>       return true;
> @@ -741,6 +776,9 @@ loongarch_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
>     if (htab->elf.dynobj == NULL)
>       htab->elf.dynobj = abfd;
>   
> +  allow_tls_transition = loongarch_elf_allow_tls_transition_p (
> +    relocs, relocs + sec->reloc_count);
> +
>     for (rel = relocs; rel < relocs + sec->reloc_count; rel++)
>       {
>         unsigned int r_type;
> @@ -818,7 +856,8 @@ loongarch_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
>         int need_dynreloc = 0;
>         int only_need_pcrel = 0;
>   
> -      r_type = loongarch_tls_transition (info, r_type, h, abfd, r_symndx);
> +      if (allow_tls_transition)
> +	r_type = loongarch_tls_transition (info, r_type, h, abfd, r_symndx);
>         switch (r_type)
>   	{
>   	case R_LARCH_GOT_PC_HI20:
> @@ -2632,7 +2671,6 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
>   				asection **local_sections)
>   {
>     Elf_Internal_Rela *rel;
> -  Elf_Internal_Rela *relend;
>     bool fatal = false;
>     asection *sreloc = elf_section_data (input_section)->sreloc;
>     struct loongarch_elf_link_hash_table *htab = loongarch_elf_hash_table (info);
> @@ -2643,8 +2681,10 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
>     bool is_dyn = elf_hash_table (info)->dynamic_sections_created;
>     asection *plt = htab->elf.splt ? htab->elf.splt : htab->elf.iplt;
>     asection *got = htab->elf.sgot;
> +  Elf_Internal_Rela *relend = relocs + input_section->reloc_count;
> +  bool allow_tls_transition =
> +    loongarch_elf_allow_tls_transition_p (relocs, relend);
>   
> -  relend = relocs + input_section->reloc_count;
>     for (rel = relocs; rel < relend; rel++)
>       {
>         unsigned int r_type = ELFNN_R_TYPE (rel->r_info);
> @@ -2789,7 +2829,12 @@ loongarch_elf_relocate_section (bfd *output_bfd, struct bfd_link_info *info,
>   
>         BFD_ASSERT (!resolved_local || defined_local);
>   
> -      relaxed_r_type = loongarch_tls_transition (info, r_type, h, input_bfd, r_symndx);
> +      relaxed_r_type =
> +	(allow_tls_transition ? loongarch_tls_transition (info, r_type,
> +							  h, input_bfd,
> +							  r_symndx)
> +			      : r_type);
> +
>         if (relaxed_r_type != r_type)
>         {
>   	howto = loongarch_elf_rtype_to_howto (input_bfd, relaxed_r_type);
> diff --git a/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp b/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp
> index 2ff06d62236..9e35940f5d6 100644
> --- a/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp
> +++ b/ld/testsuite/ld-loongarch-elf/ld-loongarch-elf.exp
> @@ -88,6 +88,20 @@ if [istarget "loongarch64-*-*"] {
>   	      "medium-call" \
>   	  ] \
>         ]
> +
> +  run_ld_link_tests \
> +      [list \
> +	  [list \
> +	      "disable TLS IE transition with TLS_IE64_PC reloc" \
> +	      "-e 0x0" "" \
> +	      "" \
> +	      {tls-ie64-notrans.s} \
> +	      [list \
> +		  [list objdump -D tls-ie64-notrans.d] \
> +	      ] \
> +	      "tls-ie64-notrans" \
> +	  ] \
> +      ]
>   }
>   
>   if [istarget "loongarch64-*-*"] {
> diff --git a/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d
> new file mode 100644
> index 00000000000..47d507a0538
> --- /dev/null
> +++ b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.d
> @@ -0,0 +1,3 @@
> +#...
> +.*pcalau12i.*
> +#pass
> diff --git a/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s
> new file mode 100644
> index 00000000000..cd8c65ff9d3
> --- /dev/null
> +++ b/ld/testsuite/ld-loongarch-elf/tls-ie64-notrans.s
> @@ -0,0 +1,7 @@
> +# it had segfaulted the linker due to invalid IE->LE transition
> +.globl _start
> +_start:
> +  la.tls.ie $a0, $a1, foo
> +
> +.section .tdata
> +foo: .word 114514