MIPS: Add options to control branch ISA checks

Complement commit 9d862524f6ae ("MIPS: Verify the ISA mode and alignment
of branch and jump targets") and add GAS and LD options to control the
checks for invalid branches between ISA modes introduced there, to help
with some handwritten code lacking `.insn' annotation for labels used as
branch targets and code produced by older versions of GCC which suffers
from the issue with branches to code that has been optimized away,
addressed with GCC commit 242424 ("MIPS/GCC: Mark trailing labels with
`.insn'"), <https://gcc.gnu.org/ml/gcc-patches/2016-11/msg01061.html>.

	bfd/
	* elfxx-mips.h (_bfd_mips_elf_insn32): Rename prototype to...
	(_bfd_mips_elf_linker_flags): ... this.  Add another parameter.
	* elfxx-mips.c (mips_elf_link_hash_table): Add
	`ignore_branch_isa' member.
	(mips_elf_perform_relocation): Do not treat an ISA mode mismatch
	in branch relocation calculation as an error if
	`ignore_branch_isa' has been set.
	(_bfd_mips_elf_insn32): Rename to...
	(_bfd_mips_elf_linker_flags): ... this.  Rename the `on'
	parameter to `insn32' and add an `ignore_branch_isa' parameter.
	Handle the new parameter.

	gas/
	* config/tc-mips.c (mips_ignore_branch_isa): New variable.
	(options): Add OPTION_IGNORE_BRANCH_ISA and
	OPTION_NO_IGNORE_BRANCH_ISA enum values.
	(md_longopts): Add "mignore-branch-isa" and
	"mno-ignore-branch-isa" options.
	(md_parse_option): Handle OPTION_IGNORE_BRANCH_ISA and
	OPTION_NO_IGNORE_BRANCH_ISA.
	(fix_bad_cross_mode_branch_p): Return FALSE if
	`mips_ignore_branch_isa' has been set.
	(md_show_usage): Add `-mignore-branch-isa' and
	`-mno-ignore-branch-isa'.

	* doc/as.texinfo (Target MIPS options): Add
	`-mignore-branch-isa' and `-mno-ignore-branch-isa' options.
	(-mignore-branch-isa, -mno-ignore-branch-isa): New options.
	* doc/c-mips.texi (MIPS Options): Add `-mignore-branch-isa' and
	`-mno-ignore-branch-isa' options.

	* testsuite/gas/mips/branch-local-ignore-2.d: New test.
	* testsuite/gas/mips/branch-local-ignore-3.d: New test.
	* testsuite/gas/mips/branch-local-ignore-n32-2.d: New test.
	* testsuite/gas/mips/branch-local-ignore-n32-3.d: New test.
	* testsuite/gas/mips/branch-local-ignore-n64-2.d: New test.
	* testsuite/gas/mips/branch-local-ignore-n64-3.d: New test.
	* testsuite/gas/mips/mips.exp: Run the new tests.

	ld/
	* emultempl/mipself.em (ignore_branch_isa): New variable.
	(mips_create_output_section_statements): Rename
	`_bfd_mips_elf_insn32' called to `_bfd_mips_elf_linker_flags',
	add `ignore_branch_isa' argument.
	(PARSE_AND_LIST_PROLOGUE): Add OPTION_IGNORE_BRANCH_ISA and
	OPTION_NO_IGNORE_BRANCH_ISA enum values.
	(PARSE_AND_LIST_LONGOPTS): Add "ignore-branch-isa" and
	"no-ignore-branch-isa" options.
	(PARSE_AND_LIST_OPTIONS): Add `--ignore-branch-isa' and
	`--no-ignore-branch-isa'.
	(PARSE_AND_LIST_ARGS_CASES): Handle OPTION_IGNORE_BRANCH_ISA and
	OPTION_NO_IGNORE_BRANCH_ISA.

	* ld.texinfo (Options specific to MIPS targets): Add
	`--ignore-branch-isa' and `--no-ignore-branch-isa' options.
	(ld and the MIPS family): Likewise.

	* testsuite/ld-mips-elf/bal-jalx-pic-ignore.d: New test.
	* testsuite/ld-mips-elf/bal-jalx-pic-ignore-n32.d: New test.
	* testsuite/ld-mips-elf/bal-jalx-pic-ignore-n64.d: New test.
	* testsuite/ld-mips-elf/unaligned-branch-ignore-2.d: New test.
	* testsuite/ld-mips-elf/unaligned-branch-ignore-r6-1: New test.
	* testsuite/ld-mips-elf/unaligned-branch-ignore-mips16: New
	test.
	* testsuite/ld-mips-elf/unaligned-branch-ignore-micromips: New
	test.
	* testsuite/ld-mips-elf/mips-elf.exp: Run the new tests.

1 files changed, 28 insertions, 20 deletions

diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index ce58c43..bda02b1 100644
--- a/bfd/elfxx-mips.c
+++ b/bfd/elfxx-mips.c
@@ -443,6 +443,9 @@ struct mips_elf_link_hash_table
   /* True if we can only use 32-bit microMIPS instructions.  */
   bfd_boolean insn32;
 
+  /* True if we suppress checks for invalid branches between ISA modes.  */
+  bfd_boolean ignore_branch_isa;
+
   /* True if we're generating code for VxWorks.  */
   bfd_boolean is_vxworks;
 
@@ -6416,31 +6419,33 @@ mips_elf_perform_relocation (struct bfd_link_info *info,
 	  value <<= 2;
 	}
 
-      if (bfd_link_pic (info) || !ok)
+      if (ok && !bfd_link_pic (info))
 	{
-	  info->callbacks->einfo
-	    (_("%X%H: Unsupported branch between ISA modes\n"),
-	     input_bfd, input_section, relocation->r_offset);
-	  return TRUE;
-	}
+	  addr = (input_section->output_section->vma
+		  + input_section->output_offset
+		  + relocation->r_offset
+		  + 4);
+	  dest = addr + (((value & 0x3ffff) ^ 0x20000) - 0x20000);
 
-      addr = (input_section->output_section->vma
-	      + input_section->output_offset
-	      + relocation->r_offset
-	      + 4);
-      dest = addr + (((value & 0x3ffff) ^ 0x20000) - 0x20000);
+	  if ((addr >> 28) << 28 != (dest >> 28) << 28)
+	    {
+	      info->callbacks->einfo
+		(_("%X%H: Cannot convert branch between ISA modes "
+		   "to JALX: relocation out of range\n"),
+		 input_bfd, input_section, relocation->r_offset);
+	      return TRUE;
+	    }
 
-      if ((addr >> 28) << 28 != (dest >> 28) << 28)
+	  /* Make this the JALX opcode.  */
+	  x = ((dest >> 2) & 0x3ffffff) | jalx_opcode << 26;
+	}
+      else if (!mips_elf_hash_table (info)->ignore_branch_isa)
 	{
 	  info->callbacks->einfo
-	    (_("%X%H: Cannot convert branch between ISA modes "
-	       "to JALX: relocation out of range\n"),
+	    (_("%X%H: Unsupported branch between ISA modes\n"),
 	     input_bfd, input_section, relocation->r_offset);
 	  return TRUE;
 	}
-
-      /* Make this the JALX opcode.  */
-      x = ((dest >> 2) & 0x3ffffff) | jalx_opcode << 26;
     }
 
   /* Try converting JAL to BAL and J(AL)R to B(AL), if the target is in
@@ -14095,12 +14100,15 @@ _bfd_mips_elf_use_plts_and_copy_relocs (struct bfd_link_info *info)
 }
 
 /* A function that the linker calls to select between all or only
-   32-bit microMIPS instructions.  */
+   32-bit microMIPS instructions, and between making or ignoring
+   branch relocation checks for invalid transitions between ISA modes.  */
 
 void
-_bfd_mips_elf_insn32 (struct bfd_link_info *info, bfd_boolean on)
+_bfd_mips_elf_linker_flags (struct bfd_link_info *info, bfd_boolean insn32,
+			    bfd_boolean ignore_branch_isa)
 {
-  mips_elf_hash_table (info)->insn32 = on;
+  mips_elf_hash_table (info)->insn32 = insn32;
+  mips_elf_hash_table (info)->ignore_branch_isa = ignore_branch_isa;
 }
 
 /* Structure for saying that BFD machine EXTENSION extends BASE.  */