[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/InputFiles.cpp

SymbolBody *elf::ObjectFile<ELFT>::createSymbolBody(const Elf_Sym *Sym) {
 
   switch (Sym->st_shndx) {
   case SHN_UNDEF:
     return elf::Symtab<ELFT>::X->addUndefined(Name, Binding, Sym->st_other,
                                               Sym->getType(),
                                               /*CanOmitFromDynSym*/ false, this)
         ->body();
   case SHN_COMMON:
+    if (Sym->st_value == 0)
+      fatal(getFilename(this) + ": common symbol '" + Name +
+            "' alignment is 0");
     return elf::Symtab<ELFT>::X->addCommon(Name, Sym->st_size, Sym->st_value,
                                            Binding, Sym->st_other,
                                            Sym->getType(), this)
         ->body();
   }
 
   switch (Binding) {
   default:

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