Don't declare all text sections at the start of the .s

The code this patch removes was there to make sure the text sections went
before the dwarf sections. That is necessary because MachO uses offsets
relative to the start of the file, so adding a section can change relaxations.

The dwarf sections were being printed at the start just to produce symbols
pointing at the start of those sections.

The underlying issue was fixed in r231898. The dwarf sections are now printed
when they are about to be used, which is after we printed the text sections.

To make sure we don't regress, the patch makes the MachO streamer assert
if CodeGen puts anything unexpected after the DWARF sections.

llvm-svn: 232842

1 files changed, 43 insertions, 6 deletions

diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
index 6246ed0..d5c7101 100644
--- a/llvm/lib/MC/MCMachOStreamer.cpp
+++ b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -40,6 +40,9 @@ private:
   /// need for local relocations. False by default.
   bool LabelSections;
 
+  bool DWARFMustBeAtTheEnd;
+  bool CreatedADWARFSection;
+
   /// HasSectionLabel - map of which sections have already had a non-local
   /// label emitted to them. Used so we don't emit extraneous linker local
   /// labels in the middle of the section.
@@ -52,9 +55,9 @@ private:
 
 public:
   MCMachOStreamer(MCContext &Context, MCAsmBackend &MAB, raw_ostream &OS,
-                  MCCodeEmitter *Emitter, bool label)
-      : MCObjectStreamer(Context, MAB, OS, Emitter),
-        LabelSections(label) {}
+                  MCCodeEmitter *Emitter, bool DWARFMustBeAtTheEnd, bool label)
+      : MCObjectStreamer(Context, MAB, OS, Emitter), LabelSections(label),
+        DWARFMustBeAtTheEnd(DWARFMustBeAtTheEnd), CreatedADWARFSection(false) {}
 
   /// state management
   void reset() override {
@@ -120,10 +123,43 @@ public:
 
 } // end anonymous namespace.
 
+static bool canGoAfterDWARF(const MCSectionMachO &MSec) {
+  // These sections are created by the assembler itself after the end of
+  // the .s file.
+  StringRef SegName = MSec.getSegmentName();
+  StringRef SecName = MSec.getSectionName();
+
+  if (SegName == "__LD" && SecName == "__compact_unwind")
+    return true;
+
+  if (SegName == "__IMPORT") {
+    if (SecName == "__jump_table")
+      return true;
+
+    if (SecName == "__pointers")
+      return true;
+  }
+
+  if (SegName == "__TEXT" && SecName == "__eh_frame")
+    return true;
+
+  if (SegName == "__DATA" && SecName == "__nl_symbol_ptr")
+    return true;
+
+  return false;
+}
+
 void MCMachOStreamer::ChangeSection(const MCSection *Section,
                                     const MCExpr *Subsection) {
   // Change the section normally.
-  MCObjectStreamer::ChangeSection(Section, Subsection);
+  bool Created = MCObjectStreamer::changeSectionImpl(Section, Subsection);
+  const MCSectionMachO &MSec = *cast<MCSectionMachO>(Section);
+  StringRef SegName = MSec.getSegmentName();
+  if (SegName == "__DWARF")
+    CreatedADWARFSection = true;
+  else if (Created && DWARFMustBeAtTheEnd && !canGoAfterDWARF(MSec))
+    assert(!CreatedADWARFSection && "Creating regular section after DWARF");
+
   // Output a linker-local symbol so we don't need section-relative local
   // relocations. The linker hates us when we do that.
   if (LabelSections && !HasSectionLabel[Section]) {
@@ -456,9 +492,10 @@ void MCMachOStreamer::FinishImpl() {
 
 MCStreamer *llvm::createMachOStreamer(MCContext &Context, MCAsmBackend &MAB,
                                       raw_ostream &OS, MCCodeEmitter *CE,
-                                      bool RelaxAll,
+                                      bool RelaxAll, bool DWARFMustBeAtTheEnd,
                                       bool LabelSections) {
-  MCMachOStreamer *S = new MCMachOStreamer(Context, MAB, OS, CE, LabelSections);
+  MCMachOStreamer *S = new MCMachOStreamer(Context, MAB, OS, CE,
+                                           DWARFMustBeAtTheEnd, LabelSections);
   if (RelaxAll)
     S->getAssembler().setRelaxAll(true);
   return S;