[Mach-O] LDC: Support emitting the DWARF __debug_info section as non-debug section

Which the linker preserves when linking the executable, so that druntime
can display file/line infos in backtraces.

See dlang/dmd@2bf7d0d.

Author: kinke

include/llvm/MC/MCObjectFileInfo.h

@@ -19,6 +19,17 @@
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/Support/CodeGen.h"
 
+// LDC-specific
+#define LDC_LLVM_SUPPORTS_MACHO_DWARF_LINE_AS_REGULAR_SECTION
+namespace ldc {
+// Mach-O: emit __debug_line section in __DWARF segment as regular section
+// (S_REGULAR) instead of default S_ATTR_DEBUG, like DMD?
+// druntime's rt.backtrace attempts to read that section from the executable,
+// and debug sections are stripped by the linker. See
+// https://github.com/dlang/dmd/commit/2bf7d0db29416eacbb01a91e6502140e354ee0ef.
+extern bool emitMachODwarfLineAsRegularSection; // defaults to false
+} // end namespace ldc
+
 namespace llvm {
 class MCContext;
 class MCSection;

lib/MC/MCObjectFileInfo.cpp

@@ -22,6 +22,11 @@
 
 using namespace llvm;
 
+// LDC-specific
+namespace ldc {
+bool emitMachODwarfLineAsRegularSection = false;
+} // end namespace ldc
+
 static bool useCompactUnwind(const Triple &T) {
   // Only on darwin.
   if (!T.isOSDarwin())
@@ -231,9 +236,12 @@ void MCObjectFileInfo::initMachOMCObjectFileInfo(const Triple &T) {
   DwarfInfoSection =
       Ctx->getMachOSection("__DWARF", "__debug_info", MachO::S_ATTR_DEBUG,
                            SectionKind::getMetadata(), "section_info");
-  DwarfLineSection =
-      Ctx->getMachOSection("__DWARF", "__debug_line", MachO::S_ATTR_DEBUG,
-                           SectionKind::getMetadata(), "section_line");
+  DwarfLineSection = Ctx->getMachOSection(
+      "__DWARF", "__debug_line",
+      // LDC-specific
+      ldc::emitMachODwarfLineAsRegularSection ? MachO::S_REGULAR
+                                              : MachO::S_ATTR_DEBUG,
+      SectionKind::getMetadata(), "section_line");
   DwarfLineStrSection =
       Ctx->getMachOSection("__DWARF", "__debug_line_str", MachO::S_ATTR_DEBUG,
                            SectionKind::getMetadata(), "section_line_str");