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.

3 files changed, 37 insertions, 0 deletions

diff --git a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
index 9e103b2..947a266 100644
--- a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
+++ b/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} \
diff --git a/ld/testsuite/ld-riscv-elf/uleb128.d b/ld/testsuite/ld-riscv-elf/uleb128.d
new file mode 100644
index 0000000..a921478
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-riscv-elf/uleb128.s b/ld/testsuite/ld-riscv-elf/uleb128.s
new file mode 100644
index 0000000..f7d23be
--- /dev/null
+++ b/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