PowerPC addpcis fix

This came up because I was looking at ld/tmpdir/addpcis.o and noticed
the odd addends on REL16DX_HA.  They ought to both be -4.  The error
crept in due REL16DX_HA howto being pc-relative (as indeed it should
be), and code at gas/write.c:1001 after this comment
	      /* Make it pc-relative.  If the back-end code has not
		 selected a pc-relative reloc, cancel the adjustment
		 we do later on all pc-relative relocs.  */
*not* cancelling the pc-relative adjustment.  So I've made a dummy
non-relative split reloc so that the generic code handles this, rather
than attempting to add hacks later in md_apply_fix which would not be
very robust.  Having the new internal reloc also makes it easy to
support

 addpcis rx,sym@ha

as an equivalent to

 addpcis rx,(sym-0f)@ha
0:

The patch also fixes overflow checking, which must test whether the
addi will overflow too since @l relocs don't have any overflow check.

Lastly, since I was poking at md_apply_fix, I arranged to have the
generic gas/write.c code emit errors for subtraction expressions where
we lack reloc support.

include/
	* elf/ppc64.h (R_PPC64_16DX_HA): New.  Expand fake reloc comment.
	* elf/ppc.h (R_PPC_16DX_HA): Likewise.
bfd/
	* reloc.c (BFD_RELOC_PPC_16DX_HA): New.
	* elf64-ppc.c (ppc64_elf_howto_raw <R_PPC64_16DX_HA>): New howto.
	(ppc64_elf_reloc_type_lookup): Translate new bfd reloc.
	(ppc64_elf_ha_reloc): Correct overflow test on REL16DX_HA.
	(ppc64_elf_relocate_section): Likewise.
	* elf32-ppc.c (ppc_elf_howto_raw <R_PPC_16DX_HA>): New howto.
	(ppc_elf_reloc_type_lookup): Translate new bfd reloc.
	(ppc_elf_check_relocs): Handle R_PPC_16DX_HA to pacify gcc.
	* libbfd.h: Regenerate.
	* bfd-in2.h: Regenerate.
gas/
	* config/tc-ppc.c (md_assemble): Use BFD_RELOC_PPC_16DX_HA for addpcis.
	(md_apply_fix): Remove fx_subsy check.  Move code converting to
	pcrel reloc earlier and handle BFD_RELOC_PPC_16DX_HA.  Remove code
	emiiting errors on seeing fx_pcrel set on unexpected relocs, as
	that is done now by the generic code via..
	* config/tc-ppc.h (TC_FORCE_RELOCATION_SUB_LOCAL): ..this. Define.
	(TC_VALIDATE_FIX_SUB): Define.
ld/
	* testsuite/ld-powerpc/addpcis.d: Define ext1 and ext2 at
	limits of addpcis range.

3 files changed, 15 insertions, 2 deletions

diff --git a/include/ChangeLog b/include/ChangeLog
index 44f242c..de28dcb 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,3 +1,8 @@
+2017-02-28  Alan Modra  <amodra@gmail.com>
+
+	* elf/ppc64.h (R_PPC64_16DX_HA): New.  Expand fake reloc comment.
+	* elf/ppc.h (R_PPC_16DX_HA): Likewise.
+
 2017-02-24  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* opcode/aarch64.h (AARCH64_OPND_SVE_ADDR_RI_S4x16)
diff --git a/include/elf/ppc.h b/include/elf/ppc.h
index 21ed671..6790cd7 100644
--- a/include/elf/ppc.h
+++ b/include/elf/ppc.h
@@ -73,10 +73,14 @@ START_RELOC_NUMBERS (elf_ppc_reloc_type)
   RELOC_NUMBER (R_PPC_ADDR30,		 37)
 
 #ifndef RELOC_MACROS_GEN_FUNC
-/* Fake relocations for branch stubs, only used internally by ld.  */
+/* Relocations only used internally by ld.  If you need to use these
+   reloc numbers, you can change them to some other unused value
+   without affecting the ABI.  They will never appear in object files.  */
   RELOC_NUMBER (R_PPC_RELAX,		 48)
   RELOC_NUMBER (R_PPC_RELAX_PLT,	 49)
   RELOC_NUMBER (R_PPC_RELAX_PLTREL24,	 50)
+/* Reloc only used internally by gas.  As above, value is unimportant.  */
+  RELOC_NUMBER (R_PPC_16DX_HA,		 51)
 #endif
 
   /* Relocs added to support TLS.  */
diff --git a/include/elf/ppc64.h b/include/elf/ppc64.h
index 307d4c2..43090dd 100644
--- a/include/elf/ppc64.h
+++ b/include/elf/ppc64.h
@@ -155,8 +155,12 @@ START_RELOC_NUMBERS (elf_ppc64_reloc_type)
   RELOC_NUMBER (R_PPC64_ENTRY,		   118)
 
 #ifndef RELOC_MACROS_GEN_FUNC
-/* Fake relocation only used internally by ld.  */
+/* Relocation only used internally by ld.  If you need to use these
+   reloc numbers, you can change them to some other unused value
+   without affecting the ABI.  They will never appear in object files.  */
   RELOC_NUMBER (R_PPC64_LO_DS_OPT,	   128)
+/* Reloc only used internally by gas.  As above, value is unimportant.  */
+  RELOC_NUMBER (R_PPC64_16DX_HA,	   129)
 #endif
 
 /* Power9 split rel16 for addpcis.  */