[LLMV][LLD] Scope OpenBSD special section handling under that ELFOSABI

As the preexisting comment (that I referred to) says:

> section names shouldn't be significant in ELF in spirit.

so scoping OSABI-specific magic name hacks to just the OSABI in question
limits the degree to which we deviate from that "spirit" for all other
OSABIs.

OpenBSD in particular is very fast moving, having added a number of
special sections, etc. in recent years. It is unclear how possible /
reasonable it is for upstream to implement all these features in any
event, but scoping like this at least mitigates the fallout for other
OSABIs systems which wish to be more slow-moving.

LLVM is likewise changed so that binaries have this ABI by default for
OpenBSD targets.

Author: Ericson2314

lld/ELF/Writer.cpp

@@ -601,10 +601,16 @@ static bool isRelroSection(const OutputSection *sec) {
   // ELF in spirit. But in reality many linker features depend on
   // magic section names.
   StringRef s = sec->name;
-  return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
-         s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
-         s == ".fini_array" || s == ".init_array" ||
-         s == ".openbsd.randomdata" || s == ".preinit_array";
+
+  bool abiAgnostic = s == ".data.rel.ro" || s == ".bss.rel.ro" ||
+                     s == ".ctors" || s == ".dtors" || s == ".jcr" ||
+                     s == ".eh_frame" || s == ".fini_array" ||
+                     s == ".init_array" || s == ".preinit_array";
+
+  bool abiSpecific =
+      config->osabi == ELFOSABI_OPENBSD && s == ".openbsd.randomdata";
+
+  return abiAgnostic || abiSpecific;
 }
 
 // We compute a rank for each section. The rank indicates where the
@@ -2281,21 +2287,26 @@ SmallVector<PhdrEntry *, 0> Writer<ELFT>::createPhdrs(Partition &part) {
     addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
         ->add(part.ehFrameHdr->getParent());
 
-  // PT_OPENBSD_MUTABLE is an OpenBSD-specific feature. That makes
-  // the dynamic linker fill the segment with zero data, like bss, but
-  // it can be treated differently.
-  if (OutputSection *cmd = findSection(".openbsd.mutable", partNo))
-    addHdr(PT_OPENBSD_MUTABLE, cmd->getPhdrFlags())->add(cmd);
-
-  // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
-  // the dynamic linker fill the segment with random data.
-  if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
-    addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
-
-  // PT_OPENBSD_SYSCALLS is an OpenBSD-specific feature. That makes
-  // the kernel and dynamic linker register system call sites.
-  if (OutputSection *cmd = findSection(".openbsd.syscalls", partNo))
-    addHdr(PT_OPENBSD_SYSCALLS, cmd->getPhdrFlags())->add(cmd);
+  // Handle OpenBSD-specific section types for OpenBSD "OS ABI".
+  //
+  // Scoped to just this "OS ABI" because, as is written below "section
+  // names shouldn't be significant in ELF in spirit".
+  if (config->osabi == ELFOSABI_OPENBSD) {
+    // PT_OPENBSD_MUTABLE makes the dynamic linker fill the segment with
+    // zero data, like bss, but it can be treated differently.
+    if (OutputSection *cmd = findSection(".openbsd.mutable", partNo))
+      addHdr(PT_OPENBSD_MUTABLE, cmd->getPhdrFlags())->add(cmd);
+
+    // PT_OPENBSD_RANDOMIZE makes the dynamic linker fill the segment
+    // with random data.
+    if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
+      addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
+
+    // PT_OPENBSD_SYSCALLS makes the kernel and dynamic linker register
+    // system call sites.
+    if (OutputSection *cmd = findSection(".openbsd.syscalls", partNo))
+      addHdr(PT_OPENBSD_SYSCALLS, cmd->getPhdrFlags())->add(cmd);
+  }
 
   if (config->zGnustack != GnuStackKind::None) {
     // PT_GNU_STACK is a special section to tell the loader to make the

llvm/include/llvm/MC/MCELFObjectWriter.h

@@ -78,6 +78,8 @@ class MCELFObjectTargetWriter : public MCObjectTargetWriter {
         return ELF::ELFOSABI_FREEBSD;
       case Triple::Solaris:
         return ELF::ELFOSABI_SOLARIS;
+      case Triple::OpenBSD:
+        return ELF::ELFOSABI_OPENBSD;
       default:
         return ELF::ELFOSABI_NONE;
     }