[ELF] -r: don't crash when a non-SHF_LINK_ORDER orphan is added before a SHF_LINK_ORDER orphan

[MaskRay]

Summary

Fixes https://github.com/ClangBuiltLinux/linux/issues/1186

If a non-SHF_LINK_ORDER orphan is added first, firstIsec->flags & SHF_LINK_ORDER
will be zero and we currently assert when calling getLinkOrderDep.

[grimar]

lld/ELF/LinkerScript.cpp

693

Probably you shouldn't use auto, because the return type is not obvious here.

lld/test/ELF/linkorder-mixed2.s

12

I'd add the Hex dump of section 'foo' check line and used CHECK-NEXT for this one, just in case.

[MaskRay]

Comments

[grimar]

LGTM

lld/ELF/LinkerScript.cpp

for (OutputSection *sec : v) {
     if (config->relocatable && (isec->flags & SHF_LINK_ORDER)) {
       // Merging two SHF_LINK_ORDER sections with different sh_link fields will
       // change their semantics, so we only merge them in -r links if they will
       // end up being linked to the same output section. The casts are fine
       // because everything in the map was created by the orphan placement code.
       auto *firstIsec = cast<InputSectionBase>(
           cast<InputSectionDescription>(sec->sectionCommands[0])
               ->sectionBases[0]);
-      if (firstIsec->getLinkOrderDep()->getOutputSection() !=
-          isec->getLinkOrderDep()->getOutputSection())
+      auto *firstIsecOut =
+          firstIsec->flags & SHF_LINK_ORDER
+              ? firstIsec->getLinkOrderDep()->getOutputSection()
+              : nullptr;
+      if (firstIsecOut != isec->getLinkOrderDep()->getOutputSection())
         continue;
     }
 
     sec->recordSection(isec);
     return nullptr;
   }
 
   OutputSection *sec = createSection(isec, outsecName);

lld/test/ELF/linkorder-mixed2.s

+# REQUIRES: x86
+## In a relocatable link, don't combine SHF_LINK_ORDER and non-SHF_LINK_ORDER
+## like we don't combine SHF_LINK_ORDER with different linked-to sections
+## (see linkerscript/linkorder-linked-to.s).
+## Test we support adding a non-SHF_LINK_ORDER section as an orphan first.
+
+# RUN: llvm-mc -filetype=obj --triple=x86_64 %s -o %t.o
+
+# RUN: ld.lld -r %t.o -o %t.ro
+# RUN: llvm-readelf -x foo %t.ro | FileCheck %s
+
+# CHECK: 0100
+
+.section foo,"a"
+.byte 0
+
+.section .text,"ax",@progbits
+ret
+
+.section foo,"ao",@progbits,.text
+.byte 1