[PATCH] [PR ld/22263] [PR ld/25694] RISC-V: Avoid dynamic TLS relocs in PIE.

[PATCH] [PR ld/22263] [PR ld/25694] RISC-V: Avoid dynamic TLS relocs in PIE.

[Nelson Chu]

From: Nelson Chu <nelson@nelson.ba.rivosinc.com>

Lots of targets already fixed the TEXTREL problem for TLS in PIE.

* For PR ld/25694,
In the check_reloc, refer to spare and loongarch, they don't need to reserve
any local dynamic reloc for TLS LE in pie/pde, and similar to other targets.
So it seems like riscv was too conservative to estimate the TLS LE before.
Just break and don't goto static_reloc for TLS LE in pie/pde can fix the
TEXTREL problem.

* For PR ld/22263,
The risc-v code for TLS GD/IE in the relocate_section seems same as MIPS port.
So similar to MIPS, pr22570, commits 9143e72c6d4d and 1cb83cac9a89, it seems
also the right way to do the same thing for risc-v.

On risc-v, fixes
FAIL: Build pr22263-1

RISC-V haven't supported the TLS transitions, so will need the same fix (use
bfd_link_dll) in the future.

bfd/
	PR ld/22263
	PR ld/25694
	* elfnn-riscv.c (riscv_elf_check_relocs): Replace bfd_link_pic with
	bfd_link_dll for TLS IE.  Don't need to reserve the local dynamic
	relocation for TLS LE in pie/pde, and report error in pic just like
	before.
	(riscv_elf_relocate_section): For TLS GD/IE, use bfd_link_dll rather
	than !bfd_link_pic in determining the dynamic symbol index.  Avoid
	the index of -1.
---
 bfd/elfnn-riscv.c | 25 +++++++++++--------------
 1 file changed, 11 insertions(+), 14 deletions(-)

diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
index a23b91ac15c..52dbf55a9f7 100644
--- a/bfd/elfnn-riscv.c
+++ b/bfd/elfnn-riscv.c
@@ -824,7 +824,7 @@ riscv_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
 	  break;
 
 	case R_RISCV_TLS_GOT_HI20:
-	  if (bfd_link_pic (info))
+	  if (bfd_link_dll (info))
 	    info->flags |= DF_STATIC_TLS;
 	  if (!riscv_elf_record_got_reference (abfd, info, h, r_symndx)
 	      || !riscv_elf_record_tls_type (abfd, h, r_symndx, GOT_TLS_IE))
@@ -920,11 +920,12 @@ riscv_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
 	  goto static_reloc;
 
 	case R_RISCV_TPREL_HI20:
+	  /* This is not allowed in the pic, but okay in pie.  */
 	  if (!bfd_link_executable (info))
 	    return bad_static_reloc (abfd, r_type, h);
 	  if (h != NULL)
 	    riscv_elf_record_tls_type (abfd, h, r_symndx, GOT_TLS_LE);
-	  goto static_reloc;
+	  break;
 
 	case R_RISCV_HI20:
 	  if (bfd_link_pic (info))
@@ -2797,24 +2798,20 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	      if (htab->elf.srelgot == NULL)
 		abort ();
 
-	      if (h != NULL)
-		{
-		  bool dyn, pic;
-		  dyn = htab->elf.dynamic_sections_created;
-		  pic = bfd_link_pic (info);
-
-		  if (WILL_CALL_FINISH_DYNAMIC_SYMBOL (dyn, pic, h)
-		      && (!pic || !SYMBOL_REFERENCES_LOCAL (info, h)))
-		    indx = h->dynindx;
-		}
+	      bool dyn = elf_hash_table (info)->dynamic_sections_created;
+	      if (h != NULL
+		  && h->dynindx != -1
+		  && WILL_CALL_FINISH_DYNAMIC_SYMBOL (dyn, bfd_link_pic (info), h)
+		  && (bfd_link_dll (info) || !SYMBOL_REFERENCES_LOCAL (info, h)))
+		indx = h->dynindx;
 
 	      /* The GOT entries have not been initialized yet.  Do it
 		 now, and emit any relocations.  */
-	      if ((bfd_link_pic (info) || indx != 0)
+	      if ((bfd_link_dll (info) || indx != 0)
 		  && (h == NULL
 		      || ELF_ST_VISIBILITY (h->other) == STV_DEFAULT
 		      || h->root.type != bfd_link_hash_undefweak))
-		    need_relocs = true;
+		need_relocs = true;
 
 	      if (tls_type & GOT_TLS_GD)
 		{
-- 
2.39.2 (Apple Git-143)

Re: [PATCH] [PR ld/22263] [PR ld/25694] RISC-V: Avoid dynamic TLS relocs in PIE.

[Nelson Chu]

[-- Attachment #1: Type: text/plain, Size: 4967 bytes --]

Committed since it should fix the pr22263-1 test.

There is still a problem mentioned by Andreas Schwab in the pr25694, that
ld still generate the unexpected R_RISCV_NONE for the pr22263-1 test after
applying this patch.  Thanks for the tips from Alan that we should have the
same condition checked for this in the relocate_section and
allocate_dynrelocs.
So here is the following fix for pr22263,
https://sourceware.org/pipermail/binutils/2023-May/127653.html

After applying the fix, it seems ld no longer generates the R_RISCV_NONE
reloc for TLS GD/IE with -pie in pr22263-1 test.
However, passing the riscv-gnu-toolchain regressions, so looks well so far.

Thanks
Nelson


On Thu, May 4, 2023 at 5:08 PM Nelson Chu <nelson@rivosinc.com> wrote:

> From: Nelson Chu <nelson@nelson.ba.rivosinc.com>
>
> Lots of targets already fixed the TEXTREL problem for TLS in PIE.
>
> * For PR ld/25694,
> In the check_reloc, refer to spare and loongarch, they don't need to
> reserve
> any local dynamic reloc for TLS LE in pie/pde, and similar to other
> targets.
> So it seems like riscv was too conservative to estimate the TLS LE before.
> Just break and don't goto static_reloc for TLS LE in pie/pde can fix the
> TEXTREL problem.
>
> * For PR ld/22263,
> The risc-v code for TLS GD/IE in the relocate_section seems same as MIPS
> port.
> So similar to MIPS, pr22570, commits 9143e72c6d4d and 1cb83cac9a89, it
> seems
> also the right way to do the same thing for risc-v.
>
> On risc-v, fixes
> FAIL: Build pr22263-1
>
> RISC-V haven't supported the TLS transitions, so will need the same fix
> (use
> bfd_link_dll) in the future.
>
> bfd/
>         PR ld/22263
>         PR ld/25694
>         * elfnn-riscv.c (riscv_elf_check_relocs): Replace bfd_link_pic with
>         bfd_link_dll for TLS IE.  Don't need to reserve the local dynamic
>         relocation for TLS LE in pie/pde, and report error in pic just like
>         before.
>         (riscv_elf_relocate_section): For TLS GD/IE, use bfd_link_dll
> rather
>         than !bfd_link_pic in determining the dynamic symbol index.  Avoid
>         the index of -1.
> ---
>  bfd/elfnn-riscv.c | 25 +++++++++++--------------
>  1 file changed, 11 insertions(+), 14 deletions(-)
>
> diff --git a/bfd/elfnn-riscv.c b/bfd/elfnn-riscv.c
> index a23b91ac15c..52dbf55a9f7 100644
> --- a/bfd/elfnn-riscv.c
> +++ b/bfd/elfnn-riscv.c
> @@ -824,7 +824,7 @@ riscv_elf_check_relocs (bfd *abfd, struct
> bfd_link_info *info,
>           break;
>
>         case R_RISCV_TLS_GOT_HI20:
> -         if (bfd_link_pic (info))
> +         if (bfd_link_dll (info))
>             info->flags |= DF_STATIC_TLS;
>           if (!riscv_elf_record_got_reference (abfd, info, h, r_symndx)
>               || !riscv_elf_record_tls_type (abfd, h, r_symndx,
> GOT_TLS_IE))
> @@ -920,11 +920,12 @@ riscv_elf_check_relocs (bfd *abfd, struct
> bfd_link_info *info,
>           goto static_reloc;
>
>         case R_RISCV_TPREL_HI20:
> +         /* This is not allowed in the pic, but okay in pie.  */
>           if (!bfd_link_executable (info))
>             return bad_static_reloc (abfd, r_type, h);
>           if (h != NULL)
>             riscv_elf_record_tls_type (abfd, h, r_symndx, GOT_TLS_LE);
> -         goto static_reloc;
> +         break;
>
>         case R_RISCV_HI20:
>           if (bfd_link_pic (info))
> @@ -2797,24 +2798,20 @@ riscv_elf_relocate_section (bfd *output_bfd,
>               if (htab->elf.srelgot == NULL)
>                 abort ();
>
> -             if (h != NULL)
> -               {
> -                 bool dyn, pic;
> -                 dyn = htab->elf.dynamic_sections_created;
> -                 pic = bfd_link_pic (info);
> -
> -                 if (WILL_CALL_FINISH_DYNAMIC_SYMBOL (dyn, pic, h)
> -                     && (!pic || !SYMBOL_REFERENCES_LOCAL (info, h)))
> -                   indx = h->dynindx;
> -               }
> +             bool dyn = elf_hash_table (info)->dynamic_sections_created;
> +             if (h != NULL
> +                 && h->dynindx != -1
> +                 && WILL_CALL_FINISH_DYNAMIC_SYMBOL (dyn, bfd_link_pic
> (info), h)
> +                 && (bfd_link_dll (info) || !SYMBOL_REFERENCES_LOCAL
> (info, h)))
> +               indx = h->dynindx;
>
>               /* The GOT entries have not been initialized yet.  Do it
>                  now, and emit any relocations.  */
> -             if ((bfd_link_pic (info) || indx != 0)
> +             if ((bfd_link_dll (info) || indx != 0)
>                   && (h == NULL
>                       || ELF_ST_VISIBILITY (h->other) == STV_DEFAULT
>                       || h->root.type != bfd_link_hash_undefweak))
> -                   need_relocs = true;
> +               need_relocs = true;
>
>               if (tls_type & GOT_TLS_GD)
>                 {
> --
> 2.39.2 (Apple Git-143)
>
>