[ELF] - X86_64: don't allow 8/16 bit dynamic relocations.

[grimar]

Summary

Having 8/16 bits dynamic relocations is incorrect.

Both gold and bfd (built from latest sources) disallow
that too.

[ruiu]

LGTM

[• espindola]

LGTM

Two suggestion for followups:

Rename isPicRel. This is not really about being position independent, it is about the dynamic linker supporting these.
Use a while list instead.

[grimar]

In D45158#1055052, @espindola wrote:

LGTM

Two suggestion for followups:

Rename isPicRel. This is not really about being position independent, it is about the dynamic linker supporting these.
Use a while list instead.

Thanks for the suggestions! I prepared D45248 and D45252 to address them.

ELF/Arch/X86_64.cpp

void X86_64<ELFT>::writePlt(uint8_t *Buf, uint64_t GotPltEntryAddr,
   memcpy(Buf, Inst, sizeof(Inst));
 
   write32le(Buf + 2, GotPltEntryAddr - PltEntryAddr - 6);
   write32le(Buf + 7, Index);
   write32le(Buf + 12, -getPltEntryOffset(Index) - 16);
 }
 
 template <class ELFT> bool X86_64<ELFT>::isPicRel(RelType Type) const {
-  return Type != R_X86_64_PC32 && Type != R_X86_64_32 &&
-         Type != R_X86_64_TPOFF32;
+  return Type != R_X86_64_8 && Type != R_X86_64_PC8 && Type != R_X86_64_16 &&
+         Type != R_X86_64_PC16 && Type != R_X86_64_32 &&
+         Type != R_X86_64_PC32 && Type != R_X86_64_TPOFF32;
 }
 
 template <class ELFT>
 void X86_64<ELFT>::relaxTlsGdToLe(uint8_t *Loc, RelType Type,
                                   uint64_t Val) const {
   // Convert
   //   .byte 0x66
   //   leaq x@tlsgd(%rip), %rdi

test/ELF/x86-64-dyn-rel-error3.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
+# RUN: not ld.lld %t.o -shared -o %t.so 2>&1 | FileCheck %s
+
+# CHECK: relocation R_X86_64_8 cannot be used against symbol foo; recompile with -fPIC
+# CHECK: relocation R_X86_64_16 cannot be used against symbol foo; recompile with -fPIC
+# CHECK: relocation R_X86_64_PC8 cannot be used against symbol foo; recompile with -fPIC
+# CHECK: relocation R_X86_64_PC16 cannot be used against symbol foo; recompile with -fPIC
+
+.global foo
+
+.data
+.byte foo       # R_X86_64_8
+.short foo      # R_X86_64_16
+.byte foo - .   # R_X86_64_PC8
+.short foo - .  # R_X86_64_PC16