[committed 1/3] MIPS/GAS: Correct BFD_RELOC_MIPS_18_PCREL_S3 calculation

[Maciej W. Rozycki]

The PC-relative R_MIPS_PC18_S3 relocation and consequently its BFD 
internal BFD_RELOC_MIPS_18_PCREL_S3 representation is calculated from 
the address of the aligned doubleword containing the location being 
relocated: (sign_extend(A) + S - (P & ~0x7)) >> 3 rather than the 
address of the location itself.  Reflect this in calculations made by 
GAS so that the relocated field is set correctly if resolved by GAS, 
such as with local symbols in the same section which do not require
relocations to be propagated to the link stage.

	gas/
	* config/tc-mips.c (md_pcrel_from) <BFD_RELOC_MIPS_18_PCREL_S3>: 
	Calculate relocation from the containing aligned doubleword.
	(tc_gen_reloc) <BFD_RELOC_MIPS_18_PCREL_S3>: Calculate the 
	addend from the containing aligned doubleword.
---
binutils-mips-gas-r6-18-pcrel-s3-from.diff
Index: binutils/gas/config/tc-mips.c
===================================================================
--- binutils.orig/gas/config/tc-mips.c	2016-06-20 23:14:55.877849627 +0100
+++ binutils/gas/config/tc-mips.c	2016-06-20 23:14:58.537382772 +0100
@@ -14606,6 +14606,11 @@ md_pcrel_from (fixS *fixP)
       /* Return the address of the delay slot.  */
       return addr + 4;
 
+    case BFD_RELOC_MIPS_18_PCREL_S3:
+      /* Return the aligned address of the doubleword containing
+         the instruction.  */
+      return addr & ~7;
+
     default:
       return addr;
     }
@@ -17224,7 +17229,15 @@ tc_gen_reloc (asection *section ATTRIBUT
 
       /* At this point, fx_addnumber is "symbol offset - pcrel address".
 	 Relocations want only the symbol offset.  */
-      reloc->addend = fixp->fx_addnumber + reloc->address;
+      switch (fixp->fx_r_type)
+	{
+	case BFD_RELOC_MIPS_18_PCREL_S3:
+	  reloc->addend = fixp->fx_addnumber + (reloc->address & ~7);
+	  break;
+	default:
+	  reloc->addend = fixp->fx_addnumber + reloc->address;
+	  break;
+	}
     }
   else if (HAVE_IN_PLACE_ADDENDS
 	   && fixp->fx_r_type == BFD_RELOC_MICROMIPS_JMP