[lld-link] Warn on exported deleting dtor

[zequanwu]

Summary

MSVC linker has this warning, so lld-link should also warn on this.

[rnk]

Seems reasonable, but I see harbormaster test failures.

[zequanwu]

Update testcase.

[rnk]

In D100606#2696117, @rnk wrote:

Seems reasonable, but I see harbormaster test failures.

The export.test seems to be crashing still both on Debian and Windows. Do you see that locally? Maybe it needs assertions to be enabled/disabled?

[zequanwu]

• Check e.sym for null. If the flag /export=foo is provided and foo is not in the object file. e.sym will be null.
• Remove $ in exported name to have same name on windows and linux.

[rnk]

lgtm

lld/COFF/Writer.cpp

void Writer::createExportTable() {
   } else if (!config->exports.empty()) {
     for (Chunk *c : edata.chunks)
       edataSec->addChunk(c);
   }
   if (!edataSec->chunks.empty()) {
     edataStart = edataSec->chunks.front();
     edataEnd = edataSec->chunks.back();
   }
+  // Warn on exported deleting destructor.
+  for (auto e : config->exports)
+    if (e.sym->getName().startswith("??_G"))
+      warn("export of deleting dtor: " + toString(*e.sym));
 }
 
 void Writer::removeUnusedSections() {
   // Remove sections that we can be sure won't get content, to avoid
   // allocating space for their section headers.
   auto isUnused = [this](OutputSection *s) {
     if (s == relocSec)
       return false; // This section is populated later.

lld/test/COFF/export-deleting-dtor.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=x86_64-windows-msvc -defsym drectve=0 %s -filetype=obj -o %t.obj
+# RUN: echo -e "EXPORTS\n  ??_G?\$Foo@H@@UEAAPEAXI@Z" > %t.def
+
+# RUN: lld-link %t.obj -entry:dllmain -dll -export:'??_G?$Foo@H@@UEAAPEAXI@Z' -out:%t.1.dll 2>&1 | FileCheck %s
+
+# RUN: lld-link %t.obj -entry:dllmain -dll -def:%t.def -out:%t.2.dll 2>&1 | FileCheck %s
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc -defsym drectve=1 %s -o %t.drectve.obj
+# RUN: lld-link %t.drectve.obj -entry:dllmain -dll -out:%t.3.dll 2>&1 | FileCheck %s
+
+# CHECK: export of deleting destructor: 
+
+        .text
+        .globl  dllmain
+        .globl  "??_G?$Foo@H@@UEAAPEAXI@Z"
+dllmain:
+        ret
+"??_G?$Foo@H@@UEAAPEAXI@Z":
+        ret
+
+.if drectve==1
+        .section .drectve
+        .ascii "-export:??_G?$Foo@H@@UEAAPEAXI@Z"
+.endif