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[binutils-gdb] MIPS/LD: Accept high-part relocations in PIC code with absolute symbols

From: Maciej W.Rozycki <macro at sourceware dot org>
To: bfd-cvs at sourceware dot org
Date: 27 Nov 2018 16:36:17 -0000
Subject: [binutils-gdb] MIPS/LD: Accept high-part relocations in PIC code with absolute symbols
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=3c7687b9cdacc243f7e23cd9b144e72b88d58817

commit 3c7687b9cdacc243f7e23cd9b144e72b88d58817
Author: Maciej W. Rozycki <macro@linux-mips.org>
Date:   Tue Nov 27 16:34:03 2018 +0000

    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 861fb55ab50a ("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.

Diff:
---
 bfd/ChangeLog                                     |  7 +++++++
 bfd/elfxx-mips.c                                  |  4 ++++
 ld/ChangeLog                                      | 17 +++++++++++++++++
 ld/testsuite/ld-mips-elf/mips-elf.exp             |  7 +++++++
 ld/testsuite/ld-mips-elf/pic-reloc-0.d            |  7 +++++++
 ld/testsuite/ld-mips-elf/pic-reloc-1.d            | 14 ++++++++++++++
 ld/testsuite/ld-mips-elf/pic-reloc-2.d            |  7 +++++++
 ld/testsuite/ld-mips-elf/pic-reloc-3.d            |  7 +++++++
 ld/testsuite/ld-mips-elf/pic-reloc-4.d            |  9 +++++++++
 ld/testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld |  6 ++++++
 ld/testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld |  6 ++++++
 ld/testsuite/ld-mips-elf/pic-reloc-j.s            | 11 +++++++++++
 ld/testsuite/ld-mips-elf/pic-reloc-lui.s          | 13 +++++++++++++
 ld/testsuite/ld-mips-elf/pic-reloc-ordinary.ld    |  6 ++++++
 14 files changed, 121 insertions(+)

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index e737f35..60eceaa 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,5 +1,12 @@
 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>
 	<R_MIPS_26, R_MICROMIPS_26_S1>: Use `info->callbacks->einfo'
 	rather than `_bfd_error_handler' to report refused relocations
diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index 298f465..1d789db 100644
--- a/bfd/elfxx-mips.c
+++ b/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
diff --git a/ld/ChangeLog b/ld/ChangeLog
index 667bc05..38a88df 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,5 +1,22 @@
 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:'
 	with `einfo'.
 	(reloc_dangerous): Likewise.
diff --git a/ld/testsuite/ld-mips-elf/mips-elf.exp b/ld/testsuite/ld-mips-elf/mips-elf.exp
index d429810..17fb1ba 100644
--- a/ld/testsuite/ld-mips-elf/mips-elf.exp
+++ b/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"
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-0.d b/ld/testsuite/ld-mips-elf/pic-reloc-0.d
new file mode 100644
index 0000000..0b2ee82
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-1.d b/ld/testsuite/ld-mips-elf/pic-reloc-1.d
new file mode 100644
index 0000000..d84a090
--- /dev/null
+++ b/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
+	\.\.\.
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-2.d b/ld/testsuite/ld-mips-elf/pic-reloc-2.d
new file mode 100644
index 0000000..fabc071
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-3.d b/ld/testsuite/ld-mips-elf/pic-reloc-3.d
new file mode 100644
index 0000000..74fc877
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-4.d b/ld/testsuite/ld-mips-elf/pic-reloc-4.d
new file mode 100644
index 0000000..0e43570
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld b/ld/testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld
new file mode 100644
index 0000000..c8848c4
--- /dev/null
+++ b/ld/testsuite/ld-mips-elf/pic-reloc-absolute-hi.ld
@@ -0,0 +1,6 @@
+SECTIONS
+{
+  bar = 0x12345678;
+  .text : { *(.text) }
+  /DISCARD/ : { *(*) }
+}
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld b/ld/testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld
new file mode 100644
index 0000000..592926e
--- /dev/null
+++ b/ld/testsuite/ld-mips-elf/pic-reloc-absolute-lo.ld
@@ -0,0 +1,6 @@
+SECTIONS
+{
+  bar = 0x2345678;
+  .text : { *(.text) }
+  /DISCARD/ : { *(*) }
+}
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-j.s b/ld/testsuite/ld-mips-elf/pic-reloc-j.s
new file mode 100644
index 0000000..2e8f9e7
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-lui.s b/ld/testsuite/ld-mips-elf/pic-reloc-lui.s
new file mode 100644
index 0000000..3ad3570
--- /dev/null
+++ b/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
diff --git a/ld/testsuite/ld-mips-elf/pic-reloc-ordinary.ld b/ld/testsuite/ld-mips-elf/pic-reloc-ordinary.ld
new file mode 100644
index 0000000..a3ed51a
--- /dev/null
+++ b/ld/testsuite/ld-mips-elf/pic-reloc-ordinary.ld
@@ -0,0 +1,6 @@
+SECTIONS
+{
+  bar = foo;
+  .text : { *(.text) }
+  /DISCARD/ : { *(*) }
+}
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