[lld] r293963 - Update comments.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Thu Feb  2 17:26:12 2017
New Revision: 293963

URL: http://llvm.org/viewvc/llvm-project?rev=293963&view=rev
Log:
Update comments.

Modified:
    lld/trunk/ELF/LinkerScript.cpp

Modified: lld/trunk/ELF/LinkerScript.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/LinkerScript.cpp?rev=293963&r1=293962&r2=293963&view=diff
==============================================================================
--- lld/trunk/ELF/LinkerScript.cpp (original)
+++ lld/trunk/ELF/LinkerScript.cpp Thu Feb  2 17:26:12 2017
@@ -696,9 +696,28 @@ static bool shouldSkip(const BaseCommand
   return Assign->Name != ".";
 }
 
-// Orphan sections are sections present in the input files which are not
-// explicitly placed into the output file by the linker script. This just
-// places them in the order already decided in OutputSections.
+// Orphan sections are sections present in the input files which are
+// not explicitly placed into the output file by the linker script.
+//
+// When the control reaches this function, Opt.Commands contains
+// output section commands for non-orphan sections only. This function
+// adds new elements for orphan sections to Opt.Commands so that all
+// sections are explicitly handled by Opt.Commands.
+//
+// Writer<ELFT>::sortSections has already sorted output sections.
+// What we need to do is to scan OutputSections vector and
+// Opt.Commands in parallel to find orphan sections. If there is an
+// output section that doesn't have a corresponding entry in
+// Opt.Commands, we will insert a new entry to Opt.Commands.
+//
+// There is some ambiguity as to where exactly a new entry should be
+// inserted, because Opt.Commands contains not only output section
+// commands but other types of commands such as symbol assignment
+// expressions. There's no correct answer here due to the lack of the
+// formal specification of the linker script. We use heuristics to
+// determine whether a new output command should be added before or
+// after another commands. For the details, look at shouldSkip
+// function.
 template <class ELFT> void LinkerScript<ELFT>::placeOrphanSections() {
   // The OutputSections are already in the correct order.
   // This loops creates or moves commands as needed so that they are in the