xtensa: fix XTENSA_NDIFF handling for PR ld/25861

Fields marked with XTENSA_NDIFF relocations are not negated, they only
have sign bits removed. Don't negate their values when relaxation is
performed. Don't add sign bits when the value is zero. Report overflow
when the result has negative sign but all significant bits are zero.

2020-04-29  Max Filippov  <jcmvbkbc@gmail.com>
bfd/
	* elf32-xtensa.c (relax_section): Don't negate diff_value for
	XTENSA_NDIFF relocations. Don't add sign bits whe diff_value
	equals 0. Report overflow when the result has negative sign but
	all significant bits are zero.

ld/
	* testsuite/ld-xtensa/relax-diff1.d: New test definition.
	* testsuite/ld-xtensa/relax-diff1.s: New test source.
	* testsuite/ld-xtensa/relax-ndiff.d: New test definition.
	* testsuite/ld-xtensa/relax-ndiff.s: New test source.
	* testsuite/ld-xtensa/xtensa.exp: (relax-diff1)
	(relax-ndiff): New tests.

8 files changed, 83 insertions, 11 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 31e8526..25453b3 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,10 @@
+2020-04-29  Max Filippov  <jcmvbkbc@gmail.com>
+
+	* elf32-xtensa.c (relax_section): Don't negate diff_value for
+	XTENSA_NDIFF relocations. Don't add sign bits whe diff_value
+	equals 0. Report overflow when the result has negative sign but
+	all significant bits are zero.
+
 2020-04-29  Gunther Nikl  <gnikl@justmail.de>
 
 	* aoutx.h (swap_std_reloc_out): Special case 64 bit relocations.
diff --git a/bfd/elf32-xtensa.c b/bfd/elf32-xtensa.c
index fded42d..4327b02 100644
--- a/bfd/elf32-xtensa.c
+++ b/bfd/elf32-xtensa.c
@@ -9670,37 +9670,44 @@ relax_section (bfd *abfd, asection *sec, struct bfd_link_info *link_info)
 		  switch (r_type)
 		    {
 		    case R_XTENSA_DIFF8:
+		      diff_mask = 0x7f;
 		      diff_value =
 			bfd_get_signed_8 (abfd, &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_DIFF16:
+		      diff_mask = 0x7fff;
 		      diff_value =
 			bfd_get_signed_16 (abfd, &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_DIFF32:
+		      diff_mask = 0x7fffffff;
 		      diff_value =
 			bfd_get_signed_32 (abfd, &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_PDIFF8:
 		    case R_XTENSA_NDIFF8:
+		      diff_mask = 0xff;
 		      diff_value =
 			bfd_get_8 (abfd, &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_PDIFF16:
 		    case R_XTENSA_NDIFF16:
+		      diff_mask = 0xffff;
 		      diff_value =
 			bfd_get_16 (abfd, &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_PDIFF32:
 		    case R_XTENSA_NDIFF32:
+		      diff_mask = 0xffffffff;
 		      diff_value =
 			bfd_get_32 (abfd, &contents[old_source_offset]);
 		      break;
 		    }
 
 		  if (r_type >= R_XTENSA_NDIFF8
-		      && r_type <= R_XTENSA_NDIFF32)
-		    diff_value = -diff_value;
+		      && r_type <= R_XTENSA_NDIFF32
+		      && diff_value)
+		    diff_value |= ~diff_mask;
 
 		  new_end_offset = offset_with_removed_text_map
 		    (&target_relax_info->action_list,
@@ -9710,43 +9717,40 @@ relax_section (bfd *abfd, asection *sec, struct bfd_link_info *link_info)
 		  switch (r_type)
 		    {
 		    case R_XTENSA_DIFF8:
-		      diff_mask = 0x7f;
 		      bfd_put_signed_8 (abfd, diff_value,
 				 &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_DIFF16:
-		      diff_mask = 0x7fff;
 		      bfd_put_signed_16 (abfd, diff_value,
 				  &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_DIFF32:
-		      diff_mask = 0x7fffffff;
 		      bfd_put_signed_32 (abfd, diff_value,
 				  &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_PDIFF8:
 		    case R_XTENSA_NDIFF8:
-		      diff_mask = 0xff;
 		      bfd_put_8 (abfd, diff_value,
 				 &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_PDIFF16:
 		    case R_XTENSA_NDIFF16:
-		      diff_mask = 0xffff;
 		      bfd_put_16 (abfd, diff_value,
 				  &contents[old_source_offset]);
 		      break;
 		    case R_XTENSA_PDIFF32:
 		    case R_XTENSA_NDIFF32:
-		      diff_mask = 0xffffffff;
 		      bfd_put_32 (abfd, diff_value,
 				  &contents[old_source_offset]);
 		      break;
 		    }
 
-		  /* Check for overflow. Sign bits must be all zeroes or all ones */
-		  if ((diff_value & ~diff_mask) != 0 &&
-		      (diff_value & ~diff_mask) != (-1 & ~diff_mask))
+		  /* Check for overflow. Sign bits must be all zeroes or
+		     all ones.  When sign bits are all ones diff_value
+		     may not be zero.  */
+		  if (((diff_value & ~diff_mask) != 0
+		       && (diff_value & ~diff_mask) != ~diff_mask)
+		      || (diff_value && (bfd_vma) diff_value == ~diff_mask))
 		    {
 		      (*link_info->callbacks->reloc_dangerous)
 			(link_info, _("overflow after relaxation"),
diff --git a/ld/ChangeLog b/ld/ChangeLog
index ae587df..43825ee 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,12 @@
+2020-04-29  Max Filippov  <jcmvbkbc@gmail.com>
+
+	* testsuite/ld-xtensa/relax-diff1.d: New test definition.
+	* testsuite/ld-xtensa/relax-diff1.s: New test source.
+	* testsuite/ld-xtensa/relax-ndiff.d: New test definition.
+	* testsuite/ld-xtensa/relax-ndiff.s: New test source.
+	* testsuite/ld-xtensa/xtensa.exp: (relax-diff1)
+	(relax-ndiff): New tests.
+
 2020-04-29  Stephen Casner  <casner@acm.org>
 
 	PR 25829
diff --git a/ld/testsuite/ld-xtensa/relax-diff1.d b/ld/testsuite/ld-xtensa/relax-diff1.d
new file mode 100644
index 0000000..900b55b
--- /dev/null
+++ b/ld/testsuite/ld-xtensa/relax-diff1.d
@@ -0,0 +1,6 @@
+#as: --text-section-literals
+#ld:
+#objdump: -s
+#...
+ 410154 06fa0006 fffa.*
+#...
diff --git a/ld/testsuite/ld-xtensa/relax-diff1.s b/ld/testsuite/ld-xtensa/relax-diff1.s
new file mode 100644
index 0000000..6cc8e2b
--- /dev/null
+++ b/ld/testsuite/ld-xtensa/relax-diff1.s
@@ -0,0 +1,18 @@
+	.globl	_start
+	.globl	_ResetVector
+	.text
+_ResetVector:
+_start:
+	.literal_position
+	movi	a2, 0x12345678
+	movi	a2, 0x12345678
+1:
+	.space	250
+2:
+	.space	65530
+3:
+	.align	4
+	.byte	1b - 2b
+	.byte	2b - 1b
+	.short	2b - 3b
+	.short	3b - 2b
diff --git a/ld/testsuite/ld-xtensa/relax-ndiff.d b/ld/testsuite/ld-xtensa/relax-ndiff.d
new file mode 100644
index 0000000..2a1cfd3
--- /dev/null
+++ b/ld/testsuite/ld-xtensa/relax-ndiff.d
@@ -0,0 +1,6 @@
+#as: --text-section-literals
+#ld:
+#objdump: -s
+#...
+ 400074 fffffff6 0000000a fff6000a f60a.*
+#...
diff --git a/ld/testsuite/ld-xtensa/relax-ndiff.s b/ld/testsuite/ld-xtensa/relax-ndiff.s
new file mode 100644
index 0000000..4e4176b
--- /dev/null
+++ b/ld/testsuite/ld-xtensa/relax-ndiff.s
@@ -0,0 +1,20 @@
+	.globl	_start
+	.globl	_ResetVector
+	.text
+_ResetVector:
+_start:
+	.literal_position
+	movi	a2, 0x12345678
+	movi	a2, 0x12345678
+1:
+	.space	10
+2:
+	.space	10
+3:
+	.align	4
+	.word	1b - 2b
+	.word	3b - 2b
+	.short	1b - 2b
+	.short	3b - 2b
+	.byte	1b - 2b
+	.byte	3b - 2b
diff --git a/ld/testsuite/ld-xtensa/xtensa.exp b/ld/testsuite/ld-xtensa/xtensa.exp
index de39887..5334bc6 100644
--- a/ld/testsuite/ld-xtensa/xtensa.exp
+++ b/ld/testsuite/ld-xtensa/xtensa.exp
@@ -27,7 +27,9 @@ run_dump_test "call_overflow"
 run_dump_test "coalesce"
 run_dump_test "diff_overflow"
 run_dump_test "lcall"
+run_dump_test "relax-diff1"
 run_dump_test "relax-loc"
+run_dump_test "relax-ndiff"
 
 run_dump_test "relax-static-pie"
 run_dump_test "relax-static-local-pie"