[2.43 PATCH] LoongArch: Fix broken DESC => IE transition for 2.43 branch

[Icenowy Zheng]

在 2024-12-19星期四的 13:23 +0800，Xi Ruoyao写道：
> If code compiled with -fPIC -mtls-dialect=desc is linked into a PDE
> or
> PIE, and the code refers to external DSO symbols, we can produce
> broken
> link unit as check_relocs expects DESC => IE transition to happen and
> emits a TLS IE entry in the GOT, but a too early "continue" in
> relax_section actually jumps over the DESC => IE transition so the
> code
> sequence is unchanged and still expecting a TLS descriptor (instead
> of
> an IE entry) in the GOT.
> 
> The bug is already fixed in master branch by commit 5c3d09c1855b
> ("LoongArch: Optimize the relaxation process") so this fix is only
> needed for the 2.43 branch.
> 
> Reported-by: Icenowy Zheng <uwu@icenowy.me>

My original case (which is compiling a full-featured Mesa) fails in
another way after applying this patch -- originally it fails because
intel_clc gets segfault (which uses std::call_once to initialize LLVM),
now it fails when linking some .so files (including libgallium).

Here's the backtrace:

```
#0  loongarch_can_trans_tls (input_bfd=<optimized out>,
info=0x555558f60b78 <link_info>, h=0x0, r_symndx=<optimized out>,
r_type=<optimized out>)
    at /var/cache/acbs/build/acbs._4a9gw_q/binutils-2.43.1/bfd/elfnn-
loongarch.c:787
#1  0x00007ffff01b44fc in loongarch_tls_transition
(input_bfd=0x55558ed785e0, info=0x555558f60b78 <link_info>, h=0x0,
r_symndx=98, r_type=111)
    at /var/cache/acbs/build/acbs._4a9gw_q/binutils-2.43.1/bfd/elfnn-
loongarch.c:844
#2  loongarch_elf_check_relocs (abfd=<optimized out>,
info=0x555558f60b78 <link_info>, sec=0x55558e1d71d8, relocs=<optimized
out>)
    at /var/cache/acbs/build/acbs._4a9gw_q/binutils-2.43.1/bfd/elfnn-
loongarch.c:985
#3  0x00007ffff01eb828 in _bfd_elf_link_iterate_on_relocs
(abfd=0x55558ed785e0, info=0x555558f60b78 <link_info>,
action=0x7ffff01b4040 <loongarch_elf_check_relocs>)
    at /var/cache/acbs/build/acbs._4a9gw_q/binutils-
2.43.1/bfd/elflink.c:4257
#4  0x0000555558ed39c0 in lang_check_relocs () at
/var/cache/acbs/build/acbs._4a9gw_q/binutils-2.43.1/ld/ldlang.c:8071
#5  lang_process () at /var/cache/acbs/build/acbs._4a9gw_q/binutils-
2.43.1/ld/ldlang.c:8383
#6  0x0000555558eb8564 in main (argc=<optimized out>, argv=<optimized
out>) at /var/cache/acbs/build/acbs._4a9gw_q/binutils-
2.43.1/ld/ldmain.c:529
```

> Closes: https://gcc.gnu.org/PR118114
> Signed-off-by: Xi Ruoyao <xry111@xry111.site>
> ---
>  bfd/elfnn-loongarch.c | 43 ++++++++++++++++++++++-------------------
> --
>  1 file changed, 22 insertions(+), 21 deletions(-)
> 
> diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
> index 312707bb00b..1c34797c2e1 100644
> --- a/bfd/elfnn-loongarch.c
> +++ b/bfd/elfnn-loongarch.c
> @@ -5326,7 +5326,7 @@ loongarch_elf_relax_section (bfd *abfd,
> asection *sec,
>      {
>        char symtype;
>        bfd_vma symval;
> -      asection *sym_sec;
> +      asection *sym_sec = NULL;
>        bool local_got = false;
>        Elf_Internal_Rela *rel = relocs + i;
>        struct elf_link_hash_entry *h = NULL;
> @@ -5418,14 +5418,33 @@ loongarch_elf_relax_section (bfd *abfd,
> asection *sec,
>               symval = h->root.u.def.value;
>               sym_sec = h->root.u.def.section;
>             }
> -         else
> -           continue;
>  
>           if (h && LARCH_REF_LOCAL (info, h))
>             local_got = true;
>           symtype = h->type;
>         }
>  
> +      /* If the conditions for tls type transition are met, type
> +        transition is performed instead of relax.
> +        During the transition from DESC->IE/LE, there are 2
> situations
> +        depending on the different configurations of the
> relax/norelax
> +        option.
> +        If the -relax option is used, the extra nops will be
> removed,
> +        and this transition is performed in pass 0.
> +        If the --no-relax option is used, nop will be retained, and
> +        this transition is performed in pass 1.  */
> +      if (IS_LOONGARCH_TLS_TRANS_RELOC (r_type)
> +         && (i + 1 != sec->reloc_count)
> +         && ELFNN_R_TYPE (rel[1].r_info) == R_LARCH_RELAX
> +         && loongarch_can_trans_tls (abfd, info, h, r_symndx,
> r_type))
> +       {
> +         loongarch_tls_perform_trans (abfd, sec, rel, h, info);
> +         r_type = ELFNN_R_TYPE (rel->r_info);
> +       }
> +
> +      if (!sym_sec)
> +       continue;
> +
>        if (sym_sec->sec_info_type == SEC_INFO_TYPE_MERGE
>            && (sym_sec->flags & SEC_MERGE))
>         {
> @@ -5453,24 +5472,6 @@ loongarch_elf_relax_section (bfd *abfd,
> asection *sec,
>  
>        symval += sec_addr (sym_sec);
>  
> -      /* If the conditions for tls type transition are met, type
> -        transition is performed instead of relax.
> -        During the transition from DESC->IE/LE, there are 2
> situations
> -        depending on the different configurations of the
> relax/norelax
> -        option.
> -        If the -relax option is used, the extra nops will be
> removed,
> -        and this transition is performed in pass 0.
> -        If the --no-relax option is used, nop will be retained, and
> -        this transition is performed in pass 1.  */
> -      if (IS_LOONGARCH_TLS_TRANS_RELOC (r_type)
> -         && (i + 1 != sec->reloc_count)
> -         && ELFNN_R_TYPE (rel[1].r_info) == R_LARCH_RELAX
> -         && loongarch_can_trans_tls (abfd, info, h, r_symndx,
> r_type))
> -       {
> -         loongarch_tls_perform_trans (abfd, sec, rel, h, info);
> -         r_type = ELFNN_R_TYPE (rel->r_info);
> -       }
> -
>        switch (r_type)
>         {
>         case R_LARCH_ALIGN:
> 
> base-commit: 834b779ad28c3cecb5ad91a1ab2af3c8453c3b3a