RISC-V: Initial ld.bfd support for TLSDESC.

Only relocation handling for now; relaxation is not implemented yet.

bfd/
    * elfnn-riscv.c (riscv_elf_check_relocs): Record GOT reference and
    paired relocation for TLSDESC_HI20.
    (riscv_elf_adjust_dynamic_symbol): Allocate GOT and reloc slots for
    TLSDESC symbols.
    (riscv_elf_size_dynamic_sections): Likewise but for local symbols.
    (tlsdescoff): New helper to determine static addend for R_TLSDESC.
    (riscv_elf_relocate_section): Ignore TLSDESC_CALL reloc for now (it is
    relaxation only).
    Handle TLSDESC_{LOAD,ADD}_LO12 as paired pcrel relocs.
    For TLS GOT slot generation, generalize the logic to handle any
    combination of (GD, IE, TLSDESC).
    Add TLSDESC Rela generation.
    * ld/testsuite/ld-riscv-elf/tls*: Add TLSDESC instruction sequences
    next to the existing GD and IE sequences. Update expectations.

bfd/elfnn-riscv.c

@@ -163,6 +163,7 @@ struct riscv_elf_link_hash_entry
 #define GOT_TLS_GD	2
 #define GOT_TLS_IE	4
 #define GOT_TLS_LE	8
+#define GOT_TLSDESC	16
   char tls_type;
 };
 
@@ -300,6 +301,7 @@ riscv_is_insn_reloc (const reloc_howto_type *howto)
 #define GOT_ENTRY_SIZE RISCV_ELF_WORD_BYTES
 #define TLS_GD_GOT_ENTRY_SIZE (RISCV_ELF_WORD_BYTES * 2)
 #define TLS_IE_GOT_ENTRY_SIZE RISCV_ELF_WORD_BYTES
+#define TLSDESC_GOT_ENTRY_SIZE (RISCV_ELF_WORD_BYTES * 2)
 /* Reserve two entries of GOTPLT for ld.so, one is used for PLT resolver,
    the other is used for link map.  Other targets also reserve one more
    entry used for runtime profile?  */
@@ -855,6 +857,12 @@ riscv_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
 	    return false;
 	  break;
 
+	case R_RISCV_TLSDESC_HI20:
+	  if (!riscv_elf_record_got_reference (abfd, info, h, r_symndx)
+	      || !riscv_elf_record_tls_type (abfd, h, r_symndx, GOT_TLSDESC))
+	    return false;
+	  break;
+
 	case R_RISCV_CALL:
 	case R_RISCV_CALL_PLT:
 	  /* These symbol requires a procedure linkage table entry.
@@ -1313,7 +1321,7 @@ allocate_dynrelocs (struct elf_link_hash_entry *h, void *inf)
       s = htab->elf.sgot;
       h->got.offset = s->size;
       dyn = htab->elf.dynamic_sections_created;
-      if (tls_type & (GOT_TLS_GD | GOT_TLS_IE))
+      if (tls_type & (GOT_TLS_GD | GOT_TLS_IE | GOT_TLSDESC))
 	{
 	  int indx = 0;
 	  bool need_reloc = false;
@@ -1334,6 +1342,14 @@ allocate_dynrelocs (struct elf_link_hash_entry *h, void *inf)
 	      if (need_reloc)
 		htab->elf.srelgot->size += sizeof (ElfNN_External_Rela);
 	    }
+
+	  /* TLSDESC needs one dynamic reloc and two GOT slots.  */
+	  if (tls_type & GOT_TLSDESC)
+	    {
+	      s->size += TLSDESC_GOT_ENTRY_SIZE;
+	      /* TLSDESC always use dynamic relocs.  */
+	      htab->elf.srelgot->size += sizeof (ElfNN_External_Rela);
+	    }
 	}
       else
 	{
@@ -1561,7 +1577,7 @@ riscv_elf_size_dynamic_sections (bfd *output_bfd, struct bfd_link_info *info)
 	  if (*local_got > 0)
 	    {
 	      *local_got = s->size;
-	      if (*local_tls_type & (GOT_TLS_GD | GOT_TLS_IE))
+	      if (*local_tls_type & (GOT_TLS_GD | GOT_TLS_IE | GOT_TLSDESC))
 		{
 		  if (*local_tls_type & GOT_TLS_GD)
 		    {
@@ -1575,6 +1591,11 @@ riscv_elf_size_dynamic_sections (bfd *output_bfd, struct bfd_link_info *info)
 		      if (bfd_link_dll (info))
 			srel->size += sizeof (ElfNN_External_Rela);
 		    }
+		  if (*local_tls_type & GOT_TLSDESC)
+		    {
+		      s->size += TLSDESC_GOT_ENTRY_SIZE;
+		      srel->size += sizeof (ElfNN_External_Rela);
+		    }
 		}
 	      else
 		{
@@ -1725,6 +1746,17 @@ tpoff (struct bfd_link_info *info, bfd_vma address)
   return address - elf_hash_table (info)->tls_sec->vma - TP_OFFSET;
 }
 
+/* Return the relocation value for a static TLSDESC relocation.  */
+
+static bfd_vma
+tlsdescoff (struct bfd_link_info *info, bfd_vma address)
+{
+  /* If tls_sec is NULL, we should have signalled an error already.  */
+  if (elf_hash_table (info)->tls_sec == NULL)
+    return 0;
+  return address - elf_hash_table (info)->tls_sec->vma;
+}
+
 /* Return the global pointer's value, or 0 if it is not in use.  */
 
 static bfd_vma
@@ -1764,6 +1796,7 @@ perform_relocation (const reloc_howto_type *howto,
     case R_RISCV_GOT_HI20:
     case R_RISCV_TLS_GOT_HI20:
     case R_RISCV_TLS_GD_HI20:
+    case R_RISCV_TLSDESC_HI20:
       if (ARCH_SIZE > 32 && !VALID_UTYPE_IMM (RISCV_CONST_HIGH_PART (value)))
 	return bfd_reloc_overflow;
       value = ENCODE_UTYPE_IMM (RISCV_CONST_HIGH_PART (value));
@@ -1774,6 +1807,8 @@ perform_relocation (const reloc_howto_type *howto,
     case R_RISCV_TPREL_LO12_I:
     case R_RISCV_TPREL_I:
     case R_RISCV_PCREL_LO12_I:
+    case R_RISCV_TLSDESC_LOAD_LO12:
+    case R_RISCV_TLSDESC_ADD_LO12:
       value = ENCODE_ITYPE_IMM (value);
       break;
 
@@ -2192,8 +2227,8 @@ riscv_elf_relocate_section (bfd *output_bfd,
       bfd_vma relocation;
       bfd_reloc_status_type r = bfd_reloc_ok;
       const char *name = NULL;
-      bfd_vma off, ie_off;
+      bfd_vma off, ie_off, desc_off;
-      bool unresolved_reloc, is_ie = false;
+      bool unresolved_reloc, is_ie = false, is_desc = false;
       bfd_vma pc = sec_addr (input_section) + rel->r_offset;
       int r_type = ELFNN_R_TYPE (rel->r_info), tls_type;
       reloc_howto_type *howto = riscv_elf_rtype_to_howto (input_bfd, r_type);
@@ -2496,6 +2531,7 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	case R_RISCV_NONE:
 	case R_RISCV_RELAX:
 	case R_RISCV_TPREL_ADD:
+	case R_RISCV_TLSDESC_CALL:
 	case R_RISCV_COPY:
 	case R_RISCV_JUMP_SLOT:
 	case R_RISCV_RELATIVE:
@@ -2843,6 +2879,22 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	  relocation = dtpoff (info, relocation);
 	  break;
 
+	case R_RISCV_TLSDESC_LOAD_LO12:
+	case R_RISCV_TLSDESC_ADD_LO12:
+	  if (rel->r_addend)
+	    {
+	      msg = _("%tlsdesc_lo with addend");
+	      r = bfd_reloc_dangerous;
+	      break;
+	    }
+
+	  if (riscv_record_pcrel_lo_reloc (&pcrel_relocs, relocation, rel,
+					   input_section, info, howto,
+					   contents))
+	      continue;
+	  r = bfd_reloc_overflow;
+	  break;
+
 	case R_RISCV_32:
 	  /* Non ABS symbol should be blocked in check_relocs.  */
 	  if (ARCH_SIZE > 32)
@@ -2908,11 +2960,16 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	    }
 	  break;
 
+	case R_RISCV_TLSDESC_HI20:
+	  is_desc = true;
+	  goto tls;
+
 	case R_RISCV_TLS_GOT_HI20:
 	  is_ie = true;
-	  /* Fall through.  */
+	  goto tls;
 
 	case R_RISCV_TLS_GD_HI20:
+	tls:
 	  if (h != NULL)
 	    {
 	      off = h->got.offset;
@@ -2925,12 +2982,16 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	    }
 
 	  tls_type = _bfd_riscv_elf_tls_type (input_bfd, h, r_symndx);
-	  BFD_ASSERT (tls_type & (GOT_TLS_IE | GOT_TLS_GD));
+	  BFD_ASSERT (tls_type & (GOT_TLS_IE | GOT_TLS_GD | GOT_TLSDESC));
-	  /* If this symbol is referenced by both GD and IE TLS, the IE
+	  /* When more than one TLS type is used, the GD slot comes first,
-	     reference's GOT slot follows the GD reference's slots.  */
+	     then IE, then finally TLSDESC.  */
 	  ie_off = 0;
-	  if ((tls_type & GOT_TLS_GD) && (tls_type & GOT_TLS_IE))
+	  if (tls_type & GOT_TLS_GD)
-	    ie_off = TLS_GD_GOT_ENTRY_SIZE;
+	    ie_off += TLS_GD_GOT_ENTRY_SIZE;
+
+	  desc_off = ie_off;
+	  if (tls_type & GOT_TLS_IE)
+	    desc_off += TLS_IE_GOT_ENTRY_SIZE;
 
 	  if ((off & 1) != 0)
 	    off &= ~1;
@@ -3012,10 +3073,29 @@ riscv_elf_relocate_section (bfd *output_bfd,
 				  htab->elf.sgot->contents + off + ie_off);
 		    }
 		}
+
+	      if (tls_type & GOT_TLSDESC)
+		{
+		  /* TLSDESC is always handled by the dynamic linker and always need
+		   * a relocation.  */
+		  bfd_put_NN (output_bfd, 0,
+			      htab->elf.sgot->contents + off + desc_off);
+		  outrel.r_offset = sec_addr (htab->elf.sgot)
+				    + off + desc_off;
+		  outrel.r_addend = 0;
+		  if (indx == 0)
+		    outrel.r_addend = tlsdescoff (info, relocation);
+		  outrel.r_info = ELFNN_R_INFO (indx, R_RISCV_TLSDESC);
+		  riscv_elf_append_rela (output_bfd, htab->elf.srelgot, &outrel);
+		}
 	    }
 
 	  BFD_ASSERT (off < (bfd_vma) -2);
-	  relocation = sec_addr (htab->elf.sgot) + off + (is_ie ? ie_off : 0);
+	  relocation = sec_addr (htab->elf.sgot) + off;
+	  if (is_ie)
+	    relocation += ie_off;
+	  else if (is_desc)
+	    relocation += desc_off;
 	  if (!riscv_record_pcrel_hi_reloc (&pcrel_relocs, pc,
 					    relocation, r_type,
 					    false))
@@ -3235,7 +3315,7 @@ riscv_elf_finish_dynamic_symbol (bfd *output_bfd,
     }
 
   if (h->got.offset != (bfd_vma) -1
-      && !(riscv_elf_hash_entry (h)->tls_type & (GOT_TLS_GD | GOT_TLS_IE))
+      && !(riscv_elf_hash_entry (h)->tls_type & (GOT_TLS_GD | GOT_TLS_IE | GOT_TLSDESC))
       && !UNDEFWEAK_NO_DYNAMIC_RELOC (info, h))
     {
       asection *sgot;

ld/testsuite/ld-riscv-elf/tls.d

@@ -2,13 +2,15 @@
 #ld: --shared tmpdir/tlslib.so
 #readelf: -Wr
 
-Relocation section '.rela.dyn' at offset 0x[0-9a-f]+ contains 5 entries:
+Relocation section '.rela.dyn' at offset 0x[0-9a-f]+ contains 7 entries:
  +Offset +Info +Type +Symbol's Value +Symbol's Name \+ Addend
 [0-9a-f]+ +[0-9a-f]+ R_RISCV_TLS_DTPMOD64 +0
 [0-9a-f]+ +[0-9a-f]+ R_RISCV_TLS_TPREL64 +4
+[0-9a-f]+ +[0-9a-f]+ R_RISCV_TLSDESC +4
 [0-9a-f]+ +[0-9a-f]+ R_RISCV_TLS_DTPMOD64 +0+ sg1 \+ 0
 [0-9a-f]+ +[0-9a-f]+ R_RISCV_TLS_DTPREL64 +0+ sg1 \+ 0
 [0-9a-f]+ +[0-9a-f]+ R_RISCV_TLS_TPREL64 +0+ sg1 \+ 0
+[0-9a-f]+ +[0-9a-f]+ R_RISCV_TLSDESC +0+ sg1 \+ 0
 
 Relocation section '.rela.plt' at offset 0x[0-9a-f]+ contains 1 entry:
  +Offset +Info +Type +Symbol's Value +Symbol's Name \+ Addend

ld/testsuite/ld-riscv-elf/tls.s

@@ -17,6 +17,13 @@ _start:
 	la.tls.ie	a0,sg1
 	add	a0,a0,tp
 
+	/* GD (TLSDESC), global var */
+.desc1:
+	auipc	a0, %tlsdesc_hi(sg1)
+	lw	t0, %tlsdesc_load_lo(.desc1)(a0)
+	addi	a0, a0, %tlsdesc_add_lo(.desc1)
+	jalr	t0, t0, %tlsdesc_call(.desc1)
+
 	/* GD, local var */
 	la.tls.gd	a0,sl1
 	call  __tls_get_addr
@@ -25,4 +32,11 @@ _start:
 	la.tls.ie	a0,sl1
 	add	a0,a0,tp
 
+	/* GD (TLSDESC), local var */
+.desc2:
+	auipc	a0, %tlsdesc_hi(sl1)
+	lw	t0, %tlsdesc_load_lo(.desc2)(a0)
+	addi	a0, a0, %tlsdesc_add_lo(.desc2)
+	jalr	t0, t0, %tlsdesc_call(.desc2)
+
 	ret

ld/testsuite/ld-riscv-elf/tlsbin.d

@@ -2,6 +2,11 @@
 #ld: -no-pie tmpdir/tlslib.so
 #readelf: -Wr
 
+Relocation section '.rela.dyn' at offset 0x[0-9a-f]+ contains 2 entries:
+ +Offset +Info +Type +Symbol's Value +Symbol's Name \+ Addend
+[0-9a-f]+ +[0-9a-f]+ R_RISCV_TLSDESC +4
+[0-9a-f]+ +[0-9a-f]+ R_RISCV_TLSDESC +0
+
 Relocation section '.rela.plt' at offset 0x[0-9a-f]+ contains 1 entry:
  +Offset +Info +Type +Symbol's Value +Symbol's Name \+ Addend
 [0-9a-f]+ +[0-9a-f]+ R_RISCV_JUMP_SLOT +[0-9a-f]+ __tls_get_addr \+ 0