[ELF] - Explicitly list supported relocations for x86 target.

[grimar]

Summary

Previously some value was returned by default for relocations by getRelExpr(),
even if relocation actually was not supported.

This is orthogonal alternative to D28094.
Instead of implementing probably useless R_386_PC8/R_386_8 relocations,
this patch uses them in a testcase to demonstrate what happens
when LLD mets unsupported relocations.

Patch passes all testcases and changes logic only for x86.
Patches for other targets can be posted separatelly.

[grimar]

Going to recheck this, sorry,

[grimar]

What I was not sure is if R_ABS correct value for R_386_TLS_LDO_32,
but that is unrelative to logic of this patch, R_ABS was returned before that change by default.
So I suggest to land this one and I'll check R_386_TLS_LDO_32 handling separatelly.

[ruiu]

LGTM

ELF/Target.cpp

387 ↗

(On Diff #83807)

Put a space before '('.

lld/trunk/ELF/Target.cpp

X86TargetInfo::X86TargetInfo() {
   GotPltEntrySize = 4;
   PltEntrySize = 16;
   PltHeaderSize = 16;
   TlsGdRelaxSkip = 2;
 }
 
 RelExpr X86TargetInfo::getRelExpr(uint32_t Type, const SymbolBody &S) const {
   switch (Type) {
-  default:
+  case R_386_16:
+  case R_386_32:
+  case R_386_TLS_LDO_32:
     return R_ABS;
   case R_386_TLS_GD:
     return R_TLSGD;
   case R_386_TLS_LDM:
     return R_TLSLD;
   case R_386_PLT32:
     return R_PLT_PC;
   case R_386_PC16:
   case R_386_PC32:
     return R_PC;
   case R_386_GOTPC:
     return R_GOTONLY_PC_FROM_END;
   case R_386_TLS_IE:
     return R_GOT;
   case R_386_GOT32:
   case R_386_GOT32X:
   case R_386_TLS_GOTIE:
     return R_GOT_FROM_END;
   case R_386_GOTOFF:
     return R_GOTREL_FROM_END;
   case R_386_TLS_LE:
     return R_TLS;
   case R_386_TLS_LE_32:
     return R_NEG_TLS;
+  default:
+    error("do not know how to handle relocation " + toString(Type) + " (" +
+          Twine(Type) + ")");
+    return R_HINT;
   }
 }
 
 RelExpr X86TargetInfo::adjustRelaxExpr(uint32_t Type, const uint8_t *Data,
                                        RelExpr Expr) const {
   switch (Expr) {
   default:
     return Expr;

lld/trunk/test/ELF/Inputs/unknown-reloc.s

+.global und
+und:

lld/trunk/test/ELF/unknown-reloc.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/unknown-reloc.s -o %t2.o
+# RUN: not ld.lld %t1.o %t2.o -o %t.out 2>&1 | FileCheck %s
+
+# CHECK: do not know how to handle relocation R_386_PC8 (23)
+# CHECK: do not know how to handle relocation R_386_8 (22)
+
+.text
+.global foo
+foo:
+
+.byte und-foo
+.byte foo