[llvm] [DirectX] Add `extract-section` to `llvm-objcopy` and implement it for `DXContainer` (PR #154804)

[James Henderson via llvm-commits]

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@@ -11,13 +11,37 @@
 #include "DXContainerWriter.h"
 #include "llvm/ObjCopy/CommonConfig.h"
 #include "llvm/ObjCopy/DXContainer/DXContainerConfig.h"
+#include "llvm/Support/raw_ostream.h"
 
 namespace llvm {
 namespace objcopy {
 namespace dxbc {
 
 using namespace object;
 
+static Error extractPartAsObject(StringRef PartName, StringRef OutFilename,
+                                 StringRef InputFilename, const Object &Obj) {
+  for (const Part &P : Obj.Parts)
+    if (P.Name == PartName) {
+      Object PartObj;
+      PartObj.Header = Obj.Header;
+      PartObj.Parts.push_back({P.Name, P.Data});
+      PartObj.recomputeHeader();
+
+      auto Write = [&OutFilename, &PartObj](raw_ostream &Out) -> Error {
+        DXContainerWriter Writer(PartObj, Out);
+        if (Error E = Writer.write())
+          return createFileError(OutFilename, std::move(E));
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jh7370 wrote:

You need a test for this error case.

https://github.com/llvm/llvm-project/pull/154804