[lld][ELF] Fix crash when relocations proceed relocated section

Fix the error generated during the linking process when the relocation section is placed before the relocated section and the relocated section is not defined in the linker script.

Author: mykouHW

lld/ELF/LinkerScript.cpp

@@ -1037,10 +1037,16 @@ void LinkerScript::addOrphanSections() {
     if (ctx.arg.relocatable && (isec->flags & SHF_LINK_ORDER))
       continue;
 
-    if (auto *sec = dyn_cast<InputSection>(isec))
-      if (InputSectionBase *rel = sec->getRelocatedSection())
-        if (auto *relIS = dyn_cast_or_null<InputSectionBase>(rel->parent))
+    if (auto *sec = dyn_cast<InputSection>(isec)) {
+      if (InputSectionBase *relocated = sec->getRelocatedSection()) {
+        // Ensure creation of OutputSection for relocated section before
+        // relocation section
+        if (auto *relIS = dyn_cast_or_null<InputSectionBase>(relocated))
           add(relIS);
+        if (auto *relIS = dyn_cast_or_null<InputSectionBase>(relocated->parent))
+          add(relIS);
+      }
+    }
     add(isec);
     if (ctx.arg.relocatable)
       for (InputSectionBase *depSec : isec->dependentSections)

lld/test/ELF/linkerscript/orphan-sections-init.s

@@ -0,0 +1,37 @@
+# REQUIRES: x86
+# RUN: rm -rf %t && mkdir -p %t
+# RUN: split-file %s %t && cd %t
+
+## Test that lld's orphan section placement can handle a relocatable link where
+## the relocation section is seen before the relocated section. 
+
+## Create a relocatable object with the relocations before the relocated section
+# RUN: llvm-mc -filetype=obj -triple=x86_64 foo.s -o foo.o
+# RUN: ld.lld -r  foo.o -T script.ld -o foo_mc.o
+
+## Rename the sections to make them orphans
+# RUN: llvm-objcopy \
+# RUN: --rename-section .text=.com.text \
+# RUN: --rename-section .rela.text=.rela.com.text \
+# RUN: foo_mc.o foo_mc.o
+
+# RUN: ld.lld -r foo_mc.o  -T script.ld -o foo_mc_after.o
+# RUN:  llvm-readelf -S foo_mc_after.o | FileCheck %s
+# CHECK:       .com.text         PROGBITS        0000000000000000 000040 000007 00  AX  0   0 16
+# CHECK-NEXT:  .rela.com.text    RELA            0000000000000000 000048 000018 18   I  4   1  8
+
+#--- foo.s
+  .text
+  .globl	foo
+  .p2align	4
+  .type	foo,@function
+foo:
+  mov $bar, %rax
+
+#--- script.ld
+SECTIONS
+{
+  .rela.text    0 : { *(.rela.text) }
+  .text         0 : { *(.text) }
+}
+