[lld] [LLD][COFF] Support /DEPENDENTLOADFLAGS[:flags] (PR #71537)

[Aleksei Nurmukhametov via llvm-commits]

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@@ -2256,6 +2262,32 @@ void Writer::fixTlsAlignment() {
   }
 }
 
+void Writer::changeLoadConfig() {
+  Symbol *sym = ctx.symtab.findUnderscore("_load_config_used");
+  auto *b = cast_if_present<DefinedRegular>(sym);
+  if (!b) {
+    if (ctx.config.guardCF != GuardCFLevel::Off)
+      warn("Control Flow Guard is enabled but '_load_config_used' is missing");
+    return;
+  }
+
+  OutputSection *sec = ctx.getOutputSection(b->getChunk());
+  uint8_t *buf = buffer->getBufferStart();
+  uint8_t *secBuf = buf + sec->getFileOff();
+  uint8_t *symBuf = secBuf + (b->getRVA() - sec->getRVA());
+  if (ctx.config.is64())
+    changeLoadConfigGuardData(
+        reinterpret_cast<coff_load_configuration64 *>(symBuf));
+  else
+    changeLoadConfigGuardData(
+        reinterpret_cast<coff_load_configuration32 *>(symBuf));
+}
+
+template <typename T> void Writer::changeLoadConfigGuardData(T *loadConfig) {
+  if (ctx.config.dependentLoadFlags)
+    loadConfig->DependentLoadFlags = ctx.config.dependentLoadFlags;
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nurmukhametov wrote:

Yes, although it looks like that the higher part of DWORD is not used at the moment ([link](https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexw#parameters)).

https://github.com/llvm/llvm-project/pull/71537