[ELF] - Do not crash when LLD synthesizes output sections with BYTE commands and -r

[grimar]

Summary

This is PR33596. Previously LLD would crash
because BYTE command synthesized output section,
but it was not assigned to Sec member of OutputSectionCommand.

Behaviour of -script and -r combination is not well defined,
but it seems after this change LLD naturally inherits behavior of
GNU linkers - creates output section requested in script and does not
crash anymore.

[ruiu]

LGTM

lld/trunk/ELF/Writer.cpp

auto J = std::find_if(
       [](BaseCommand *Cmd) { return isa<OutputSectionCommand>(Cmd); });
   I = J.base();
   while (I != E && shouldSkip(*I))
     ++I;
   return I;
 }
 
 template <class ELFT> void Writer<ELFT>::sortSections() {
+  if (Script->Opt.HasSections)
+    Script->adjustSectionsBeforeSorting();
+
   // Don't sort if using -r. It is not necessary and we want to preserve the
   // relative order for SHF_LINK_ORDER sections.
   if (Config->Relocatable)
       return;
 
-  if (Script->Opt.HasSections)
-    Script->adjustSectionsBeforeSorting();
-
   for (BaseCommand *Base : Script->Opt.Commands)
     if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
       if (OutputSection *Sec = Cmd->Sec)
         Sec->SortRank = getSectionRank(Sec);
 
   if (!Script->Opt.HasSections) {
     // We know that all the OutputSectionCommands are contiguous in
     // this case.

lld/trunk/test/ELF/relocatable-script.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux -o %t1.o %s
+# RUN: echo "SECTIONS { .foo : { BYTE(0x0) } }" > %t.script
+# RUN: ld.lld -r %t1.o -script %t.script -o %t2.o
+# RUN: llvm-readobj -sections %t2.o | FileCheck %s
+
+# CHECK:  Name: .foo