RISC-V: Support subtraction of .uleb128.

https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/96d6e190e9fc04a8517f9ff7fb9aed3e9876cbd6

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.

1 files changed, 54 insertions, 0 deletions

diff --git a/bfd/elfxx-riscv.c b/bfd/elfxx-riscv.c
index bd0c7c8..7f45324 100644
--- a/bfd/elfxx-riscv.c
+++ b/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