MIPS/LD: Accept high-part relocations in PIC code with absolute symbols

Accept R_MIPS_HI16, R_MIPS_HIGHER and R_MIPS_HIGHEST relocations and
their compressed counterparts in PIC code where the symbol referred is
absolute.  Such an operation is meaningful, because an absolute symbol
effectively is a constant the calculation of the value of which has been
deferred to the static link time, and which is not going to change any
further at the dynamic load time.  Therefore there is no need ever to
refuse the use of these relocations with such symbols, as the resulting
run-time value observed by the program will be correct even in PIC code.

This is not the case with R_MIPS_26 and its compressed counterparts,
because the run-time value calculated by the instructions these
relocations are used with depends on the address of the instruction
itself, and that can change according to the base address used by the
dynamic loader.  Therefore these relocations have to continue being
rejected in PIC code even with absolute symbols.

This allows successful linking of code that relies on previous linker
behavior up to commit 861fb55ab5 ("Defer allocation of R_MIPS_REL32
GOT slots"), <https://sourceware.org/ml/binutils/2008-08/msg00096.html>,
which introduced the problematic check missing this special exception
for absolute symbols.

	bfd/
	* elfxx-mips.c (_bfd_mips_elf_check_relocs) <R_MIPS16_HI16>
	<R_MIPS_HI16, R_MIPS_HIGHER, R_MIPS_HIGHEST, R_MICROMIPS_HI16>
	<R_MICROMIPS_HIGHER, R_MICROMIPS_HIGHEST>: Also accept an
	absolute symbol in PIC code.

	ld/
	* testsuite/ld-mips-elf/pic-reloc-0.d: New test.
	* testsuite/ld-mips-elf/pic-reloc-1.d: New test.
	* testsuite/ld-mips-elf/pic-reloc-2.d: New test.
	* testsuite/ld-mips-elf/pic-reloc-3.d: New test.
	* testsuite/ld-mips-elf/pic-reloc-4.d: New test.
	* testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld: New test
	linker script.
	* testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld: New test
	linker script.
	* testsuite/ld-mips-elf/pic-reloc-ordinary.ld: New test linker
	script.
	* testsuite/ld-mips-elf/pic-reloc-j.s: New test source.
	* testsuite/ld-mips-elf/pic-reloc-lui.s: New test source.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new tests.

bfd/ChangeLog

@@ -1,3 +1,10 @@
+2018-11-27  Maciej W. Rozycki  <macro@linux-mips.org>
+
+	* elfxx-mips.c (_bfd_mips_elf_check_relocs) <R_MIPS16_HI16>
+	<R_MIPS_HI16, R_MIPS_HIGHER, R_MIPS_HIGHEST, R_MICROMIPS_HI16>
+	<R_MICROMIPS_HIGHER, R_MICROMIPS_HIGHEST>: Also accept an
+	absolute symbol in PIC code.
+
 2018-11-27  Maciej W. Rozycki  <macro@linux-mips.org>
 
 	* elfxx-mips.c (_bfd_mips_elf_check_relocs) <R_MIPS16_26>

bfd/elfxx-mips.c

@@ -9061,6 +9061,10 @@ _bfd_mips_elf_check_relocs (bfd *abfd, struct bfd_link_info *info,
 	      if (r_symndx == STN_UNDEF)
 		break;
 
+	      /* Likewise an absolute symbol.  */
+	      if (bfd_is_abs_symbol (&h->root))
+		break;
+
 	      /* R_MIPS_HI16 against _gp_disp is used for $gp setup,
 		 and has a special meaning.  */
 	      if (!NEWABI_P (abfd) && h != NULL

ld/ChangeLog

@@ -1,3 +1,20 @@
+2018-11-27  Maciej W. Rozycki  <macro@linux-mips.org>
+
+	* testsuite/ld-mips-elf/pic-reloc-0.d: New test.
+	* testsuite/ld-mips-elf/pic-reloc-1.d: New test.
+	* testsuite/ld-mips-elf/pic-reloc-2.d: New test.
+	* testsuite/ld-mips-elf/pic-reloc-3.d: New test.
+	* testsuite/ld-mips-elf/pic-reloc-4.d: New test.
+	* testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld: New test
+	linker script.
+	* testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld: New test
+	linker script.
+	* testsuite/ld-mips-elf/pic-reloc-ordinary.ld: New test linker
+	script.
+	* testsuite/ld-mips-elf/pic-reloc-j.s: New test source.
+	* testsuite/ld-mips-elf/pic-reloc-lui.s: New test source.
+	* testsuite/ld-mips-elf/mips-elf.exp: Run the new tests.
+
 2018-11-27  Maciej W. Rozycki  <macro@linux-mips.org>
 
 	* ldmain.c (reloc_overflow): Use `%H:' rather than `%P: %H:'

ld/testsuite/ld-mips-elf/mips-elf.exp

@@ -1629,3 +1629,10 @@ if $has_abi(n64) {
     run_mips_undefweak_test "shared library (n64, microMIPS, hidden)" \
 						    n64 dso umips hidden
 }
+
+# PIC relocation acceptance tests.
+run_dump_test "pic-reloc-0"
+run_dump_test "pic-reloc-1"
+run_dump_test "pic-reloc-2"
+run_dump_test "pic-reloc-3"
+run_dump_test "pic-reloc-4"

ld/testsuite/ld-mips-elf/pic-reloc-0.d

@@ -0,0 +1,7 @@
+#name: MIPS PIC relocation 0
+#ld: -shared -T pic-reloc-ordinary.ld
+#target: [check_shared_lib_support]
+#source: pic-reloc-lui.s
+#error: \A[^\n]*: in function `foo':\n
+#error:   \(\.text\+0x0\): relocation R_MIPS_HI16 against `bar' cannot be used when making a shared object; recompile with -fPIC\n
+#error:   \(\.text\+0x8\): relocation R_MIPS_HI16 against `bar' cannot be used when making a shared object; recompile with -fPIC\Z

ld/testsuite/ld-mips-elf/pic-reloc-1.d

@@ -0,0 +1,14 @@
+#name: MIPS PIC relocation 1
+#ld: -shared -T pic-reloc-absolute-hi.ld
+#objdump: -d --prefix-addresses --show-raw-insn
+#target: [check_shared_lib_support]
+#source: pic-reloc-lui.s
+
+.*: +file format .*mips.*
+
+Disassembly of section \.text:
+[0-9a-f]+ <[^>]*> 3c021234 	lui	v0,0x1234
+[0-9a-f]+ <[^>]*> 24425678 	addiu	v0,v0,22136
+[0-9a-f]+ <[^>]*> 3c021234 	lui	v0,0x1234
+[0-9a-f]+ <[^>]*> 24425678 	addiu	v0,v0,22136
+	\.\.\.

ld/testsuite/ld-mips-elf/pic-reloc-2.d

@@ -0,0 +1,7 @@
+#name: MIPS PIC relocation 2
+#ld: -shared -T pic-reloc-ordinary.ld
+#target: [check_shared_lib_support]
+#source: pic-reloc-j.s
+#error: \A[^\n]*: in function `foo':\n
+#error:   \(\.text\+0x0\): relocation R_MIPS_26 against `bar' cannot be used when making a shared object; recompile with -fPIC\n
+#error:   \(\.text\+0x8\): relocation R_MIPS_26 against `bar' cannot be used when making a shared object; recompile with -fPIC\Z

ld/testsuite/ld-mips-elf/pic-reloc-3.d

@@ -0,0 +1,7 @@
+#name: MIPS PIC relocation 3
+#ld: -shared -T pic-reloc-absolute-lo.ld
+#target: [check_shared_lib_support]
+#source: pic-reloc-j.s
+#error: \A[^\n]*: in function `foo':\n
+#error:   \(\.text\+0x0\): relocation R_MIPS_26 against `bar' cannot be used when making a shared object; recompile with -fPIC\n
+#error:   \(\.text\+0x8\): relocation R_MIPS_26 against `bar' cannot be used when making a shared object; recompile with -fPIC\Z

ld/testsuite/ld-mips-elf/pic-reloc-4.d

@@ -0,0 +1,9 @@
+#name: MIPS PIC relocation 4
+#ld: -shared -T pic-reloc-absolute-hi.ld
+#target: [check_shared_lib_support]
+#source: pic-reloc-j.s
+#error: \A[^\n]*: in function `foo':\n
+#error:   \(\.text\+0x0\): relocation R_MIPS_26 against `bar' cannot be used when making a shared object; recompile with -fPIC\n
+#error:   \(\.text\+0x8\): relocation R_MIPS_26 against `bar' cannot be used when making a shared object; recompile with -fPIC\n
+#error:   \(\.text\+0x0\): relocation truncated to fit: R_MIPS_26 against `bar'\n
+#error:   \(\.text\+0x8\): relocation truncated to fit: R_MIPS_26 against `bar'\Z

ld/testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld

@@ -0,0 +1,6 @@
+SECTIONS
+{
+  bar = 0x12345678;
+  .text : { *(.text) }
+  /DISCARD/ : { *(*) }
+}

ld/testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld

@@ -0,0 +1,6 @@
+SECTIONS
+{
+  bar = 0x2345678;
+  .text : { *(.text) }
+  /DISCARD/ : { *(*) }
+}

ld/testsuite/ld-mips-elf/pic-reloc-j.s

@@ -0,0 +1,11 @@
+	.text
+	.globl	foo
+	.ent	foo
+foo:
+	j	bar
+	j	bar
+	.end	foo
+
+# Force some (non-delay-slot) zero bytes, to make 'objdump' print ...
+	.align	4, 0
+	.space	16

ld/testsuite/ld-mips-elf/pic-reloc-lui.s

@@ -0,0 +1,13 @@
+	.text
+	.globl	foo
+	.ent	foo
+foo:
+	lui	$2, %hi(bar)
+	addiu	$2, %lo(bar)
+	lui	$2, %hi(bar)
+	addiu	$2, %lo(bar)
+	.end	foo
+
+# Force some (non-delay-slot) zero bytes, to make 'objdump' print ...
+	.align	4, 0
+	.space	16

ld/testsuite/ld-mips-elf/pic-reloc-ordinary.ld

@@ -0,0 +1,6 @@
+SECTIONS
+{
+  bar = foo;
+  .text : { *(.text) }
+  /DISCARD/ : { *(*) }
+}