[ELF] - Use SignExtend when reading R_386_PC16 addend.

[grimar]

Summary

This is the same as D29490, but for R_386_PC16

[grimar]

Simplified testcase.

[ruiu]

I think you want to do the same thing for all PC-relative relocations.

[grimar]

Will be merged with D29490

ELF/Target.cpp

uint64_t X86TargetInfo::getImplicitAddend(const uint8_t *Buf,
                                           uint32_t Type) const {
   switch (Type) {
   default:
     return 0;
   case R_386_8:
   case R_386_PC8:
     return *Buf;
   case R_386_16:
-  case R_386_PC16:
     return read16le(Buf);
+  case R_386_PC16:
+    return SignExtend64<16>(read16le(Buf));
   case R_386_32:
   case R_386_GOT32:
   case R_386_GOT32X:
   case R_386_GOTOFF:
   case R_386_GOTPC:
   case R_386_PC32:
   case R_386_PLT32:
   case R_386_TLS_LE:

test/ELF/i386-pc16-addend.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux-gnu %s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux-gnu %S/Inputs/i386-pc8.s -o %t2.o
+# RUN: llvm-objdump -d %t1.o | FileCheck %s --check-prefix=OBJDISASM
+
+## Show that we have relocation with addend = 0xFFFE(-2),
+## we do sign extend for its value in the code.
+# OBJDISASM:      Disassembly of section .text:
+# OBJDISASM-NEXT: .text:
+# OBJDISASM-NEXT:   0: fe ff
+
+# RUN: ld.lld %t1.o %t2.o -o %t.out
+# RUN: llvm-objdump -d %t.out | FileCheck %s --check-prefix=DISASM
+# RUN: llvm-readobj -symbols %t.out | FileCheck %s --check-prefix=SYM
+# DISASM:      Disassembly of section .text:
+# DISASM-NEXT: .text:
+# DISASM-NEXT:    11000: 02 00
+## 0x11004 - 0x11000 + addend = 0x2
+# SYM:     Symbol {
+# SYM:       Name: und
+# SYM-NEXT:  Value: 0x11004
+
+.code16
+.word und-.-2