Revert "MC: Allocate initial fragment and define section symbol in changeSection" (#150736)

Reverts llvm/llvm-project#150574

This is causing a test failure on AArch64 MacOS bots:
https://lab.llvm.org/buildbot/#/builders/190/builds/24187

1 files changed, 14 insertions, 1 deletions

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index ae8dffc..6099bb8 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -559,7 +559,20 @@ void ELFWriter::computeSymbolTable(const RevGroupMapTy &RevGroupMap) {
     } else {
       const MCSectionELF &Section =
           static_cast<const MCSectionELF &>(Symbol.getSection());
-      assert(Section.isRegistered());
+
+      // We may end up with a situation when section symbol is technically
+      // defined, but should not be. That happens because we explicitly
+      // pre-create few .debug_* sections to have accessors.
+      // And if these sections were not really defined in the code, but were
+      // referenced, we simply error out.
+      if (!Section.isRegistered()) {
+        assert(static_cast<const MCSymbolELF &>(Symbol).getType() ==
+               ELF::STT_SECTION);
+        Ctx.reportError(SMLoc(),
+                        "Undefined section reference: " + Symbol.getName());
+        continue;
+      }
+
       if (Mode == NonDwoOnly && isDwoSection(Section))
         continue;
       MSD.SectionIndex = Section.getOrdinal();