RISC-V: Support subtraction of .uleb128.

96d6e190e9

There are some known limitations for now,

* Do not shrink the length of the uleb128 value, even if the value is reduced
after relaxations.  Also reports error if the length grows up.

* The R_RISCV_SET_ULEB128 needs to be paired with and be placed before the
R_RISCV_SUB_ULEB128.

bfd/
	* bfd-in2.h: Regenerated.
	* elfnn-riscv.c (perform_relocation): Perform R_RISCV_SUB_ULEB128 and
	R_RISCV_SET_ULEB128 relocations.  Do not shrink the length of the
	uleb128 value, and report error if the length grows up.  Called the
	generic functions, _bfd_read_unsigned_leb128 and _bfd_write_unsigned_leb128,
	to encode the uleb128 into the section contents.
	(riscv_elf_relocate_section): Make sure that the R_RISCV_SET_ULEB128
	must be paired with and be placed before the R_RISCV_SUB_ULEB128.
	* elfxx-riscv.c (howto_table): Added R_RISCV_SUB_ULEB128 and
	R_RISCV_SET_ULEB128.
	(riscv_reloc_map): Likewise.
	(riscv_elf_ignore_reloc): New function.
	* libbfd.h: Regenerated.
	* reloc.c (BFD_RELOC_RISCV_SET_ULEB128, BFD_RELOC_RISCV_SUB_ULEB128):
	New relocations to support .uleb128 subtraction.
gas/
	* config/tc-riscv.c (md_apply_fix): Added BFD_RELOC_RISCV_SET_ULEB128
	and BFD_RELOC_RISCV_SUB_ULEB128.
	(s_riscv_leb128): Updated to allow uleb128 subtraction.
	(riscv_insert_uleb128_fixes): New function, scan uleb128 subtraction
	expressions and insert fixups for them.
	(riscv_md_finish): Called riscv_insert_uleb128_fixes for all sections.
include/
	* elf/riscv.h ((R_RISCV_SET_ULEB128, (R_RISCV_SUB_ULEB128): Defined.
ld/
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Updated.
	* testsuite/ld-riscv-elf/uleb128*: New testcase for uleb128 subtraction.
binutils/
	* testsuite/binutils-all/nm.exp: Updated since RISCV supports .uleb128.

bfd/bfd-in2.h

@@ -5394,6 +5394,8 @@ number for the SBIC, SBIS, SBI and CBI instructions  */
   BFD_RELOC_RISCV_SET16,
   BFD_RELOC_RISCV_SET32,
   BFD_RELOC_RISCV_32_PCREL,
+  BFD_RELOC_RISCV_SET_ULEB128,
+  BFD_RELOC_RISCV_SUB_ULEB128,
 
 /* Renesas RL78 Relocations.  */
   BFD_RELOC_RL78_NEG8,

bfd/elfnn-riscv.c

@@ -1792,6 +1792,55 @@ perform_relocation (const reloc_howto_type *howto,
 	value = ENCODE_CITYPE_LUI_IMM (RISCV_CONST_HIGH_PART (value));
       break;
 
+    /* SUB_ULEB128 must be applied after SET_ULEB128, so we only write the
+       value back for SUB_ULEB128 should be enough.  */
+    case R_RISCV_SET_ULEB128:
+      break;
+    case R_RISCV_SUB_ULEB128:
+      {
+	unsigned int len = 0;
+	_bfd_read_unsigned_leb128 (input_bfd, contents + rel->r_offset, &len);
+
+	/* Clean the contents value to zero (0x80), but keep the original
+	   length.  */
+	bfd_byte *p = contents + rel->r_offset;
+	bfd_byte *endp = p + len - 1;
+	memset (p, 0x80, len - 1);
+	*(endp) = 0;
+
+	/* Make sure the length of the new uleb128 value within the
+	   original (available) length.  */
+	unsigned int new_len = 0;
+	unsigned int val_t = value;
+	do
+	  {
+	    new_len++;
+	    val_t >>= 7;
+	  }
+	while (val_t);
+	if (new_len > len)
+	  {
+	    _bfd_error_handler
+	      (_("final size of uleb128 value at offset 0x%lx in %pA from "
+		 "%pB exceeds available space"),
+	       (long) rel->r_offset, input_section, input_bfd);
+	    return bfd_reloc_dangerous;
+	  }
+	else
+	  {
+	    p = _bfd_write_unsigned_leb128 (p, endp, value);
+	    BFD_ASSERT (p);
+
+	    /* If the length of the value is reduced and shorter than the
+	       original uleb128 length, then _bfd_write_unsigned_leb128 may
+	       clear the 0x80 to 0x0 for the last byte that was written.
+	       So reset it to keep the the original uleb128 length.  */
+	    if (--p < endp)
+	      *p |= 0x80;
+	  }
+	return bfd_reloc_ok;
+      }
+
     case R_RISCV_32:
     case R_RISCV_64:
     case R_RISCV_ADD8:
@@ -2086,6 +2135,8 @@ riscv_elf_relocate_section (bfd *output_bfd,
   Elf_Internal_Shdr *symtab_hdr = &elf_symtab_hdr (input_bfd);
   struct elf_link_hash_entry **sym_hashes = elf_sym_hashes (input_bfd);
   bfd_vma *local_got_offsets = elf_local_got_offsets (input_bfd);
+  bfd_vma uleb128_set_vma = 0;
+  Elf_Internal_Rela *uleb128_set_rel = NULL;
   bool absolute;
 
   if (!riscv_init_pcrel_relocs (&pcrel_relocs))
@@ -2427,6 +2478,38 @@ riscv_elf_relocate_section (bfd *output_bfd,
 	  /* These require no special handling beyond perform_relocation.  */
 	  break;
 
+	case R_RISCV_SET_ULEB128:
+	  if (uleb128_set_rel == NULL)
+	    {
+	      /* Saved for later usage.  */
+	      uleb128_set_vma = relocation;
+	      uleb128_set_rel = rel;
+	      continue;
+	    }
+	  else
+	    {
+	      msg = ("Mismatched R_RISCV_SET_ULEB128, it must be paired with"
+		     "and applied before R_RISCV_SUB_ULEB128");
+	      r = bfd_reloc_dangerous;
+	    }
+	  break;
+
+	case R_RISCV_SUB_ULEB128:
+	  if (uleb128_set_rel != NULL
+	      && uleb128_set_rel->r_offset == rel->r_offset)
+	    {
+	      relocation = uleb128_set_vma - relocation;
+	      uleb128_set_vma = 0;
+	      uleb128_set_rel = NULL;
+	    }
+	  else
+	    {
+	      msg = ("Mismatched R_RISCV_SUB_ULEB128, it must be paired with"
+		     "and applied after R_RISCV_SET_ULEB128");
+	      r = bfd_reloc_dangerous;
+	    }
+	  break;
+
 	case R_RISCV_GOT_HI20:
 	  if (h != NULL)
 	    {

bfd/elfxx-riscv.c

@@ -38,6 +38,8 @@
    relocations for the debug info.  */
 static bfd_reloc_status_type riscv_elf_add_sub_reloc
   (bfd *, arelent *, asymbol *, void *, asection *, bfd *, char **);
+static bfd_reloc_status_type riscv_elf_ignore_reloc
+  (bfd *, arelent *, asymbol *, void *, asection *, bfd *, char **);
 
 /* The relocation table used for SHT_RELA sections.  */
 
@@ -844,6 +846,39 @@ static reloc_howto_type howto_table[] =
 	 0,				/* src_mask */
 	 0xffffffff,			/* dst_mask */
 	 false),			/* pcrel_offset */
+
+  /* Reserved for R_RISCV_PLT32.  */
+  EMPTY_HOWTO (59),
+
+  /* N-bit in-place setting, for unsigned-leb128 local label subtraction.  */
+  HOWTO (R_RISCV_SET_ULEB128,		/* type */
+	 0,				/* rightshift */
+	 0,				/* size */
+	 0,				/* bitsize */
+	 false,				/* pc_relative */
+	 0,				/* bitpos */
+	 complain_overflow_dont,	/* complain_on_overflow */
+	 riscv_elf_ignore_reloc,	/* special_function */
+	 "R_RISCV_SET_ULEB128",		/* name */
+	 false,				/* partial_inplace */
+	 0,				/* src_mask */
+	 0,				/* dst_mask */
+	 false),			/* pcrel_offset */
+
+  /* N-bit in-place addition, for unsigned-leb128 local label subtraction.  */
+  HOWTO (R_RISCV_SUB_ULEB128,		/* type */
+	 0,				/* rightshift */
+	 0,				/* size */
+	 0,				/* bitsize */
+	 false,				/* pc_relative */
+	 0,				/* bitpos */
+	 complain_overflow_dont,	/* complain_on_overflow */
+	 riscv_elf_ignore_reloc,	/* special_function */
+	 "R_RISCV_SUB_ULEB128",		/* name */
+	 false,				/* partial_inplace */
+	 0,				/* src_mask */
+	 0,				/* dst_mask */
+	 false),			/* pcrel_offset */
 };
 
 /* A mapping from BFD reloc types to RISC-V ELF reloc types.  */
@@ -905,6 +940,8 @@ static const struct elf_reloc_map riscv_reloc_map[] =
   { BFD_RELOC_RISCV_SET16, R_RISCV_SET16 },
   { BFD_RELOC_RISCV_SET32, R_RISCV_SET32 },
   { BFD_RELOC_RISCV_32_PCREL, R_RISCV_32_PCREL },
+  { BFD_RELOC_RISCV_SET_ULEB128, R_RISCV_SET_ULEB128 },
+  { BFD_RELOC_RISCV_SUB_ULEB128, R_RISCV_SUB_ULEB128 },
 };
 
 /* Given a BFD reloc type, return a howto structure.  */
@@ -1010,6 +1047,23 @@ riscv_elf_add_sub_reloc (bfd *abfd,
   return bfd_reloc_ok;
 }
 
+/* Special handler for relocations which don't have to be relocated.
+   This function just simply return bfd_reloc_ok.  */
+
+static bfd_reloc_status_type
+riscv_elf_ignore_reloc (bfd *abfd ATTRIBUTE_UNUSED,
+			arelent *reloc_entry,
+			asymbol *symbol ATTRIBUTE_UNUSED,
+			void *data ATTRIBUTE_UNUSED,
+			asection *input_section,
+			bfd *output_bfd,
+			char **error_message ATTRIBUTE_UNUSED)
+{
+  if (output_bfd != NULL)
+    reloc_entry->address += input_section->output_offset;
+  return bfd_reloc_ok;
+}
+
 /* Always add the IMPLICIT for the SUBSET.  */
 
 static bool

bfd/libbfd.h

@@ -2417,6 +2417,8 @@ static const char *const bfd_reloc_code_real_names[] = { "@@uninitialized@@",
   "BFD_RELOC_RISCV_SET16",
   "BFD_RELOC_RISCV_SET32",
   "BFD_RELOC_RISCV_32_PCREL",
+  "BFD_RELOC_RISCV_SET_ULEB128",
+  "BFD_RELOC_RISCV_SUB_ULEB128",
   "BFD_RELOC_RL78_NEG8",
   "BFD_RELOC_RL78_NEG16",
   "BFD_RELOC_RL78_NEG24",

bfd/reloc.c

@@ -5048,6 +5048,10 @@ ENUMX
   BFD_RELOC_RISCV_SET32
 ENUMX
   BFD_RELOC_RISCV_32_PCREL
+ENUMX
+  BFD_RELOC_RISCV_SET_ULEB128
+ENUMX
+  BFD_RELOC_RISCV_SUB_ULEB128
 ENUMDOC
   RISC-V relocations.
 

binutils/testsuite/binutils-all/nm.exp

@@ -246,8 +246,6 @@ if [is_elf_format] {
     # Test nm --line-numbers on DWARF-4 debug info.    
     set testname "nm --line-numbers on DWARF-4 debug info"
 
-    # The RISCV target does not (currently) support .uleb128.
-    setup_xfail "riscv*-*-*"
     # The SH targets complain that the pseudo-ops used to construct
     # the DWARF data are misaligned.
     setup_xfail "sh*-*-*"

gas/config/tc-riscv.c

@@ -3950,6 +3950,9 @@ md_apply_fix (fixS *fixP, valueT *valP, segT seg ATTRIBUTE_UNUSED)
     case BFD_RELOC_RISCV_SUB32:
     case BFD_RELOC_RISCV_SUB64:
     case BFD_RELOC_RISCV_RELAX:
+    /* cvt_frag_to_fill () has called output_leb128 ().  */
+    case BFD_RELOC_RISCV_SET_ULEB128:
+    case BFD_RELOC_RISCV_SUB_ULEB128:
       break;
 
     case BFD_RELOC_RISCV_TPREL_HI20:
@@ -4714,8 +4717,11 @@ s_riscv_leb128 (int sign)
   char *save_in = input_line_pointer;
 
   expression (&exp);
-  if (exp.X_op != O_constant)
-    as_bad (_("non-constant .%cleb128 is not supported"), sign ? 's' : 'u');
+  if (sign && exp.X_op != O_constant)
+    as_bad (_("non-constant .sleb128 is not supported"));
+  else if (!sign && exp.X_op != O_constant && exp.X_op != O_subtract)
+    as_bad (_(".uleb128 only supports constant or subtract expressions"));
+
   demand_empty_rest_of_line ();
 
   input_line_pointer = save_in;
@@ -4835,12 +4841,58 @@ riscv_set_public_attributes (void)
     riscv_write_out_attrs ();
 }
 
+/* Scan uleb128 subtraction expressions and insert fixups for them.
+   e.g., .uleb128 .L1 - .L0
+   Because relaxation may change the value of the subtraction, we
+   must resolve them at link-time.  */
+
+static void
+riscv_insert_uleb128_fixes (bfd *abfd ATTRIBUTE_UNUSED,
+			    asection *sec, void *xxx ATTRIBUTE_UNUSED)
+{
+  segment_info_type *seginfo = seg_info (sec);
+  struct frag *fragP;
+
+  subseg_set (sec, 0);
+
+  for (fragP = seginfo->frchainP->frch_root;
+       fragP; fragP = fragP->fr_next)
+    {
+      expressionS *exp, *exp_dup;
+
+      if (fragP->fr_type != rs_leb128  || fragP->fr_symbol == NULL)
+	continue;
+
+      exp = symbol_get_value_expression (fragP->fr_symbol);
+
+      if (exp->X_op != O_subtract)
+	continue;
+
+      /* Only unsigned leb128 can be handled.  */
+      gas_assert (fragP->fr_subtype == 0);
+      exp_dup = xmemdup (exp, sizeof (*exp), sizeof (*exp));
+      exp_dup->X_op = O_symbol;
+      exp_dup->X_op_symbol = NULL;
+
+      /* Insert relocations to resolve the subtraction at link-time.
+	 Emit the SET relocation first in riscv.  */
+      exp_dup->X_add_symbol = exp->X_add_symbol;
+      fix_new_exp (fragP, fragP->fr_fix, 0,
+		   exp_dup, 0, BFD_RELOC_RISCV_SET_ULEB128);
+      exp_dup->X_add_symbol = exp->X_op_symbol;
+      fix_new_exp (fragP, fragP->fr_fix, 0,
+		   exp_dup, 0, BFD_RELOC_RISCV_SUB_ULEB128);
+    }
+}
+
 /* Called after all assembly has been done.  */
 
 void
 riscv_md_finish (void)
 {
   riscv_set_public_attributes ();
+  if (riscv_opts.relax)
+    bfd_map_over_sections (stdoutput, riscv_insert_uleb128_fixes, NULL);
 }
 
 /* Adjust the symbol table.  */

include/elf/riscv.h

@@ -87,6 +87,9 @@ START_RELOC_NUMBERS (elf_riscv_reloc_type)
   RELOC_NUMBER (R_RISCV_SET32, 56)
   RELOC_NUMBER (R_RISCV_32_PCREL, 57)
   RELOC_NUMBER (R_RISCV_IRELATIVE, 58)
+  /* Reserved 59 for R_RISCV_PLT32.  */
+  RELOC_NUMBER (R_RISCV_SET_ULEB128, 60)
+  RELOC_NUMBER (R_RISCV_SUB_ULEB128, 61)
 END_RELOC_NUMBERS (R_RISCV_max)
 
 /* Processor specific flags for the ELF header e_flags field.  */

ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp

@@ -172,6 +172,7 @@ if [istarget "riscv*-*-*"] {
     run_dump_test "attr-merge-priv-spec-failed-06"
     run_dump_test "attr-phdr"
     run_dump_test "relax-max-align-gp"
+    run_dump_test "uleb128"
     run_ld_link_tests [list \
 	[list "Weak reference 32" "-T weakref.ld -m[riscv_choose_ilp32_emul]" "" \
 	    "-march=rv32i -mabi=ilp32" {weakref32.s} \

ld/testsuite/ld-riscv-elf/uleb128.d

@@ -0,0 +1,18 @@
+#source: uleb128.s
+#as: -march=rv32ic
+#ld: -melf32lriscv
+#objdump: -d
+
+.*:[ 	]+file format .*
+
+Disassembly of section .text:
+
+.* <_start>:
+.*jal.*<bar>
+.*jal.*<bar>
+.*jal.*<bar>
+.*jal.*<bar>
+.*jal.*<bar>
+.*jal.*<bar>
+.*:[ 	]+0e0c.*
+#pass

ld/testsuite/ld-riscv-elf/uleb128.s

@@ -0,0 +1,18 @@
+.text
+.globl bar
+.globl _start
+.option rvc
+.align 2
+_start:
+.L0:
+        .rept 6
+        call bar
+        .endr
+.align 2
+.L1:
+        .uleb128 .L1 - .L0
+        .uleb128 .L2 - .L0
+.L2:
+.align 2
+bar:
+        nop