[lld] lld: add support for NOCROSSREFS(_TO) (PR #95714)

[Peter Smith via llvm-commits]

================
@@ -2358,3 +2358,62 @@ template void elf::scanRelocations<ELF32LE>();
 template void elf::scanRelocations<ELF32BE>();
 template void elf::scanRelocations<ELF64LE>();
 template void elf::scanRelocations<ELF64BE>();
+
+static bool isNoCrefFromSection(const CrossRefList &list,
+                                const OutputSection *section) {
+  const auto *begin =
+      list.firstOnly ? list.refs.begin() + 1 : list.refs.begin();
+
+  return std::find(begin, list.refs.end(), section->name) != list.refs.end();
+}
+
+static bool isNoCrefToSection(const CrossRefList &list,
+                              const OutputSection *section) {
+  if (list.firstOnly)
+    return list.refs[0] == section->name;
+
+  return std::find(list.refs.begin(), list.refs.end(), section->name) !=
+         list.refs.end();
+}
+
+void elf::checkNoCrossRefs() {
+  // Basic brute-force algorithm, since in reality NOCROSSRES lists are quite
+  // small.
+  //
+  // Idea is to traverse all relocations in all sections and report if
+  // prohibited reference was found. Note that NOCROSSREFS works with output section
+  // names.
+  for (ELFFileBase *file : ctx.objectFiles) {
+    auto sections = file->getSections();
+    std::string message = "";
+
+    for (size_t i = 0; i < sections.size(); ++i) {
+      if (sections[i]) {
+        StringRef sectionName = sections[i]->name;
+
+        if (const auto *outSec = dyn_cast_or_null<OutputSection>(sections[i]->parent)) {
+          for (const auto &refs : script->nocrossrefs) {
+            if (isNoCrefFromSection(refs, outSec)) {
+
+              for (const auto &j : sections[i]->relocations) {
+                if (auto *def = dyn_cast<Defined>(j.sym)) {
+                  const auto *outSecSym =
+                      cast<InputSection>(def->section)->getParent();
+
+                  if (isNoCrefToSection(refs, outSecSym)) {
+                    message +=
----------------
smithp35 wrote:

This could give you an awful lot of error messsages for large sections with lots of relocations. Does GNU ld give an error per relocation or only one per output section cross-reference?


https://github.com/llvm/llvm-project/pull/95714