[ELF] - Do not crash if common symbol has alignment 0.

[grimar]

Summary

id_000024,sig_08,src_000002,op_arith16,pos_94,val_-16

contains a common symbol with zero alignment. I did not found
in specification that it is correct (like it says that for sections) and
since we were fine living without it, I made it an error instead
of assigning 1 like we do for sections.

[ruiu]

LGTM. We could handle alignment 0 as alignment 1 here, but we shouldn't do that. This is a crash bug, but we've never received a bug report about it, so it is very likely that there's no such object file out there that assumes alignment 0 = alignment 1.

[emaste]

it is very likely that there's no such object file out there

Agreed, and it will be easy for a user to track down if they ever do receive this error message.

[ruiu]

I'd move this to InputFiles.cpp.

[grimar]

• Addressed review comments.

[• rafael]

LGTM

[ruiu]

LGTM

ELF/Symbols.cpp

DefinedSynthetic<ELFT>::DefinedSynthetic(StringRef N, uintX_t Value,
                                          OutputSectionBase<ELFT> *Section)
     : Defined(SymbolBody::DefinedSyntheticKind, N, STV_HIDDEN, 0 /* Type */),
       Value(Value), Section(Section) {}
 
 DefinedCommon::DefinedCommon(StringRef N, uint64_t Size, uint64_t Alignment,
                              uint8_t StOther, uint8_t Type, InputFile *File)
     : Defined(SymbolBody::DefinedCommonKind, N, StOther, Type),
       Alignment(Alignment), Size(Size) {
+  if (Alignment == 0)
+    fatal(getFilename(File) + ": common symbol '" + N + "' alignment is 0");
   this->File = File;
 }
 
 InputFile *Lazy::fetch() {
   if (auto *S = dyn_cast<LazyArchive>(this))
     return S->fetch();
   return cast<LazyObject>(this)->fetch();
 }

test/ELF/invalid/common-symbol-alignment.s

+# REQUIRES: x86
+
+## common-symbol-alignment.elf contains common symbol with zero alignment.
+# RUN: not ld.lld %S/Inputs/common-symbol-alignment.elf \
+# RUN:   -o %t 2>&1 | FileCheck %s
+# CHECK: common symbol 'bar' alignment is 0