[lld-macho] Have inputOrder default to less than INT_MAX

[int3]

Summary

We make it less than INT_MAX in order not to conflict with the ordering
of zerofill sections, which must always be placed at the end of their
segment.

This is the more structural fix for the issue addressed in D104596: [lld/mac] Make sure __thread_ptrs is in front of __thread_bss.

[int3]

style

[thakis]

Great, thanks!

[smeenai]

lld/MachO/OutputSection.h

27

Any particular significance to the 1024?

[int3]

lld/MachO/OutputSection.h

27

nope, I just wanted a nice round number

lld/MachO/Driver.cpp

for (const Arg *arg : args.filtered(OPT_sectcreate)) {
           for (const SubsectionEntry &entry : map) {
             if (auto concatIsec = dyn_cast<ConcatInputSection>(entry.isec))
               if (concatIsec->isCoalescedWeak())
                 continue;
             inputSections.push_back(entry.isec);
           }
         }
       }
+      assert(inputSections.size() < UnspecifiedInputOrder);
     }
 
     if (config->deadStrip)
       markLive();
 
     // Write to an output file.
     if (target->wordSize == 8)
       writeResult<LP64>();

lld/MachO/OutputSection.h

 #include <limits>
 
 namespace lld {
 namespace macho {
 
 class InputSection;
 class OutputSegment;
 
+// The default order value for OutputSections that are not constructed from
+// InputSections (i.e. SyntheticSections). We make it less than INT_MAX in order
+// not to conflict with the ordering of zerofill sections, which must always be
+// placed at the end of their segment.
+constexpr int UnspecifiedInputOrder = std::numeric_limits<int>::max() - 1024;
+
 // Output sections represent the finalized sections present within the final
 // linked executable. They can represent special sections (like the symbol
 // table), or represent coalesced sections from the various inputs given to the
 // linker with the same segment / section name.
 class OutputSection {
 public:
   enum Kind {
     ConcatKind,
public:
 
   virtual void writeTo(uint8_t *buf) const = 0;
 
   StringRef name;
   OutputSegment *parent = nullptr;
   // For output sections that don't have explicit ordering requirements, their
   // output order should be based on the order of the input sections they
   // contain.
-  int inputOrder = std::numeric_limits<int>::max();
+  int inputOrder = UnspecifiedInputOrder;
 
   uint32_t index = 0;
   uint64_t addr = 0;
   uint64_t fileOff = 0;
   uint32_t align = 1;
   uint32_t flags = 0;
   uint32_t reserved1 = 0;
   uint32_t reserved2 = 0;

lld/MachO/OutputSegment.h

public:
   void sortOutputSections();
 
   const std::vector<OutputSection *> &getSections() const { return sections; }
   size_t numNonHiddenSections() const;
 
   uint64_t fileOff = 0;
   uint64_t fileSize = 0;
   uint64_t vmSize = 0;
-  int inputOrder = std::numeric_limits<int>::max();
+  int inputOrder = UnspecifiedInputOrder;
   StringRef name;
   uint32_t maxProt = 0;
   uint32_t initProt = 0;
   uint8_t index;
 
 private:
   std::vector<OutputSection *> sections;
 };