[ObjCopy][DX] Support for -dump-section flag

This adds support for the -dump-section=<section>=<file> flag for the
DXContainer file format. This flag dumps the contents of a named section
to the specified file.

This flag is particularly handy for ripping DXIL bitcode out of the
object files so that we can use LLVM tools to inspect and operate on
the bitcode. To facilitate that workflow this flag also strips the
program headers from parts containing DXIL so that the resulting file is
a valid bitcode file.
../llvm/lib/ObjCopy/DXContainer/DXContainerObjcopy.cpp
../llvm/test/tools/llvm-objcopy/DXContainer/dump-section.yaml

Author: llvm-beanz

llvm/lib/ObjCopy/ConfigManager.cpp

@@ -122,14 +122,14 @@ ConfigManager::getDXContainerConfig() const {
   if (!Common.AddGnuDebugLink.empty() || !Common.SplitDWO.empty() ||
       !Common.AllocSectionsPrefix.empty() ||
       Common.DiscardMode != DiscardType::None || !Common.AddSection.empty() ||
-      !Common.DumpSection.empty() || !Common.KeepSection.empty() ||
-      !Common.SectionsToRename.empty() || !Common.SetSectionAlignment.empty() ||
-      !Common.SetSectionFlags.empty() || !Common.SetSectionType.empty() ||
-      Common.ExtractDWO || Common.OnlyKeepDebug || Common.StripAllGNU ||
-      Common.StripDWO || Common.StripDebug || Common.StripNonAlloc ||
-      Common.StripSections || Common.StripUnneeded ||
-      Common.DecompressDebugSections || Common.GapFill != 0 ||
-      Common.PadTo != 0 || Common.ChangeSectionLMAValAll != 0 ||
+      !Common.KeepSection.empty() || !Common.SectionsToRename.empty() ||
+      !Common.SetSectionAlignment.empty() || !Common.SetSectionFlags.empty() ||
+      !Common.SetSectionType.empty() || Common.ExtractDWO ||
+      Common.OnlyKeepDebug || Common.StripAllGNU || Common.StripDWO ||
+      Common.StripDebug || Common.StripNonAlloc || Common.StripSections ||
+      Common.StripUnneeded || Common.DecompressDebugSections ||
+      Common.GapFill != 0 || Common.PadTo != 0 ||
+      Common.ChangeSectionLMAValAll != 0 ||
       !Common.ChangeSectionAddress.empty()) {
     return createStringError(llvm::errc::invalid_argument,
                              "option is not supported for DXContainer");

llvm/lib/ObjCopy/DXContainer/DXContainerObjcopy.cpp

@@ -9,8 +9,10 @@
 #include "llvm/ObjCopy/DXContainer/DXContainerObjcopy.h"
 #include "DXContainerReader.h"
 #include "DXContainerWriter.h"
+#include "llvm/BinaryFormat/DXContainer.h"
 #include "llvm/ObjCopy/CommonConfig.h"
 #include "llvm/ObjCopy/DXContainer/DXContainerConfig.h"
+#include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 
 namespace llvm {
@@ -42,7 +44,40 @@ static Error extractPartAsObject(StringRef PartName, StringRef OutFilename,
                          "part '%s' not found", PartName.str().c_str());
 }
 
+static Error dumpPartToFile(StringRef PartName, StringRef Filename,
+                            StringRef InputFilename, Object &Obj) {
+  for (const Part &P : Obj.Parts) {
+    if (P.Name == PartName) {
+      ArrayRef<uint8_t> Contents = P.Data;
+      // For parts containing llvm bitcode, don't dump the program headers so
+      // that we get a valid .bc file.
+      if (PartName == "DXIL" || PartName == "STAT")
+        Contents = Contents.drop_front(sizeof(llvm::dxbc::ProgramHeader));
+      Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
+          FileOutputBuffer::create(Filename, Contents.size());
+      if (!BufferOrErr)
+        return createFileError(Filename, BufferOrErr.takeError());
+      std::unique_ptr<FileOutputBuffer> Buf = std::move(*BufferOrErr);
+      llvm::copy(Contents, Buf->getBufferStart());
+      if (Error E = Buf->commit())
+        return createFileError(Filename, std::move(E));
+      return Error::success();
+    }
+  }
+  return createFileError(Filename,
+                         std::make_error_code(std::errc::invalid_argument),
+                         "part '%s' not found", PartName.str().c_str());
+}
+
 static Error handleArgs(const CommonConfig &Config, Object &Obj) {
+  for (StringRef Flag : Config.DumpSection) {
+    StringRef SecName;
+    StringRef FileName;
+    std::tie(SecName, FileName) = Flag.split("=");
+    if (Error E = dumpPartToFile(SecName, FileName, Config.InputFilename, Obj))
+      return E;
+  }
+
   // Extract all sections before any modifications.
   for (StringRef Flag : Config.ExtractSection) {
     StringRef SectionName;