MSP430: Support relocations for subtract expressions in .uleb128 directives

Link-time relaxations of branches are common for MSP430, given that GCC
can generate pessimal branch instructions, and the
-mcode-region=either/-mdata-region=either options to shuffle sections
can further change the type of branch instruction required.

These relaxations can result in invalid code when .uleb128
directives, used in the .gcc_except_table section, are used to calculate
the distance between two labels. A value for the .uleb128 directive is
calculated at assembly-time, and can't be updated at link-time, even if
relaxation causes the distance between the labels to change.

This patch adds relocations for subtract expressions in .uleb128
directives, to allow the linker to re-calculate the value of these
expressions after relaxation has been performed.

bfd/ChangeLog:
	* bfd-in2.h (bfd_reloc_code_real): Add
	BFD_RELOC_MSP430_{SET,SUB}_ULEB128.
	* elf32-msp430.c (msp430_elf_ignore_reloc): New.
	(elf_msp430_howto_table): Add R_MSP430{,X}_GNU_{SET,SUB}_ULEB128.
	(msp430_reloc_map): Add R_MSP430_GNU_{SET,SUB}_ULEB128.
	(msp430x_reloc_map): Add R_MSP430X_GNU_{SET,SUB}_ULEB128.
	(write_uleb128): New.
	(msp430_final_link_relocate): Handle R_MSP430{,X}_GNU_{SET,SUB}_ULEB128.
	* libbfd.c (_bfd_write_unsigned_leb128): New.
	* libbfd.h (_bfd_write_unsigned_leb128): New prototype.
	Add BFD_RELOC_MSP430_{SET,SUB}_ULEB128.
	* reloc.c: Document BFD_RELOC_MSP430_{SET,SUB}_ULEB128.

binutils/ChangeLog:
	* readelf.c (target_specific_reloc_handling): Handle
	R_MSP430{,X}_GNU_{SET,SUB}_ULEB128.

gas/ChangeLog:
	* config/tc-msp430.c (msp430_insert_uleb128_fixes): New.
	(msp430_md_end): Call msp430_insert_uleb128_fixes.

include/ChangeLog:
	* elf/msp430.h (elf_msp430_reloc_type): Add
	R_MSP430_GNU_{SET,SUB}_ULEB128.
	(elf_msp430x_reloc_type): Add R_MSP430X_GNU_{SET,SUB}_ULEB128.

ld/ChangeLog:
	* testsuite/ld-msp430-elf/msp430-elf.exp: Run new tests.
	* testsuite/ld-msp430-elf/uleb128.s: New test.
	* testsuite/ld-msp430-elf/uleb128_430.d: New test.
	* testsuite/ld-msp430-elf/uleb128_430x.d: New test.

4 files changed, 57 insertions, 0 deletions

diff --git a/ld/testsuite/ld-msp430-elf/msp430-elf.exp b/ld/testsuite/ld-msp430-elf/msp430-elf.exp
index a2fa4db..875b413 100644
--- a/ld/testsuite/ld-msp430-elf/msp430-elf.exp
+++ b/ld/testsuite/ld-msp430-elf/msp430-elf.exp
@@ -176,6 +176,9 @@ set msp430arraytests {
 
 run_ld_link_tests $msp430arraytests
 
+run_dump_test uleb128_430
+run_dump_test uleb128_430x
+
 # Don't run further tests when msp430 ISA is selected
 if {[string match "*-mcpu=msp430 *" [board_info [target_info name] multilib_flags]]
   || [string match "*-mcpu=msp430" [board_info [target_info name] multilib_flags]]} {
diff --git a/ld/testsuite/ld-msp430-elf/uleb128.s b/ld/testsuite/ld-msp430-elf/uleb128.s
new file mode 100644
index 0000000..598ee0c
--- /dev/null
+++ b/ld/testsuite/ld-msp430-elf/uleb128.s
@@ -0,0 +1,34 @@
+.data
+	.global	bar
+	.balign 2
+bar:
+	.short	42
+	.short	43
+
+	.global foo
+foo:
+.skip 0xff
+
+	.global	foo2
+	.balign 2
+foo2:
+	.short	4
+
+.text
+
+  .balign 2
+  .global byte
+byte:
+  .word foo-bar
+  .word foo2-bar
+
+  .global uleb
+  .balign 2
+uleb:
+	.uleb128 foo-bar  ; this value can be stored in one byte
+	.uleb128 foo2-bar ; this value requires 2 bytes
+
+  .balign 2
+  .global _start
+  _start:
+  nop
diff --git a/ld/testsuite/ld-msp430-elf/uleb128_430.d b/ld/testsuite/ld-msp430-elf/uleb128_430.d
new file mode 100644
index 0000000..5104552
--- /dev/null
+++ b/ld/testsuite/ld-msp430-elf/uleb128_430.d
@@ -0,0 +1,10 @@
+#source: uleb128.s
+#as: -mcpu=msp430
+#ld:
+#objdump: -sj.text
+
+.*:[ 	]+file format .*
+
+Contents of section .text:
+ [0-9a-f]+ 04000401 04840200.*
+#pass
diff --git a/ld/testsuite/ld-msp430-elf/uleb128_430x.d b/ld/testsuite/ld-msp430-elf/uleb128_430x.d
new file mode 100644
index 0000000..e808a53
--- /dev/null
+++ b/ld/testsuite/ld-msp430-elf/uleb128_430x.d
@@ -0,0 +1,10 @@
+#source: uleb128.s
+#as: -mcpu=msp430x
+#ld:
+#objdump: -sj.text
+
+.*:[ 	]+file format .*
+
+Contents of section .text:
+ [0-9a-f]+ 04000401 04840200.*
+#pass