[ELF] - Do sign extend for addends of R_386_8, R_386_16 relocations

[grimar]

Summary

The same we did earlier for PC ones,
currenly LLD fails to link kernel, reporting relocation out of range because of this.

I prepared separate test, because had to involve -Ttext option and
that would change currect pc8/pc16 test significantly , what probably not worth to do.

[ruiu]

Maybe we need to sign extend everything? In other words, is there any relocation that we shouldn't sign extend?

[grimar]

In D29714#671060, @ruiu wrote:

Maybe we need to sign extend everything? In other words, is there any relocation that we shouldn't sign extend?

From my understanding we should extend only relocations that have addend value shorter than target size.

I mean we return 64 bit value from getImplicitAddend(), it is then assigned to uintX_t. So for i386 case for example we want to extend all relocations that are not reading 32 bits,
as anyways value is truncated later.
So I believe, for i386 this patch is all what else needed for it's relocations, all other ones are working with 32 bits already.

[grimar]

In D29714#671060, @ruiu wrote:

Maybe we need to sign extend everything? In other words, is there any relocation that we shouldn't sign extend?

So just to be clear - we sure can extend everything, but there is no point to do that, its excessive job, so I would probably extend only "short" addends.

lld/trunk/ELF/Target.cpp

 }
 
 int64_t X86TargetInfo::getImplicitAddend(const uint8_t *Buf,
                                          uint32_t Type) const {
   switch (Type) {
   default:
     return 0;
   case R_386_8:
-    return *Buf;
   case R_386_PC8:
     return SignExtend64<8>(*Buf);
   case R_386_16:
-    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:

lld/trunk/test/ELF/i386-reloc8-reloc16-addend.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux-gnu %s -o %t1.o
+
+# RUN: ld.lld -Ttext=0x0 %t1.o -o %t.out
+# RUN: llvm-objdump -s -t %t.out | FileCheck %s
+# CHECK:      Contents of section .text:
+# CHECK-NEXT:  0000 020100 
+## 0x3 + addend(-1) = 0x02
+## 0x3 + addend(-2) = 0x0100
+# CHECK: SYMBOL TABLE:
+# CHECK: 00000003 .und
+
+.byte  und-1
+.short und-2
+
+.section .und, "ax"
+und: