[ObjCopy][DX] Support for -dump-section flag (llvm#159999)

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.

---------

Co-authored-by: Justin Bogner <[email protected]>

Author: 2 people

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 +44,47 @@ 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) {
+  auto PartIter = llvm::find_if(
+      Obj.Parts, [&PartName](const Part &P) { return P.Name == PartName; });
+  if (PartIter == Obj.Parts.end())
+    return createFileError(Filename,
+                           std::make_error_code(std::errc::invalid_argument),
+                           "part '%s' not found", PartName.str().c_str());
+  ArrayRef<uint8_t> Contents = PartIter->Data;
+  // The DXContainer format is a bit odd because the part-specific headers are
+  // contained inside the part data itself. For parts that contain LLVM bitcode
+  // when we dump the part we want to skip the part-specific header so that we
+  // get a valid .bc file that we can inspect. All the data contained inside the
+  // program header is pulled out of the bitcode, so the header can be
+  // reconstructed if needed from the bitcode itself. More comprehensive
+  // documentation on the DXContainer format can be found at
+  // https://llvm.org/docs/DirectX/DXContainer.html.
+
+  if (PartName == "DXIL" || PartName == "STAT")
+    Contents = Contents.drop_front(sizeof(llvm::dxbc::ProgramHeader));
+  if (Contents.empty())
+    return createFileError(Filename, object_error::parse_failed,
+                           "part '%s' is empty", PartName.str().c_str());
+  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();
+}
+
 static Error handleArgs(const CommonConfig &Config, Object &Obj) {
+  for (StringRef Flag : Config.DumpSection) {
+    auto [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;

llvm/test/tools/llvm-objcopy/DXContainer/dump-section-errors.yaml

@@ -0,0 +1,27 @@
+# RUN: yaml2obj %s -o %t.dxbc
+# RUN: not llvm-objcopy --dump-section=FKE0=%t.fek0 %t.dxbc 2>&1 | FileCheck %s --check-prefix=CHECK-ZEROSIZE -DFILE=%t.fek0
+# RUN: not llvm-objcopy --dump-section=FKE3=%t.fek1 %t.dxbc 2>&1 | FileCheck %s --check-prefix=CHECK-MISSING -DFILE=%t.fek1
+# RUN: not llvm-objcopy --dump-section=FKE2=%t/does_not_exist/.fek2 %t.dxbc 2>&1 | FileCheck %s --check-prefix=CHECK-BAD-PATH -DFILE=%t/does_not_exist/.fek2 -DMSG=%errc_ENOENT
+
+# CHECK-ZEROSIZE: error: '[[FILE]]': part 'FKE0' is empty
+# CHECK-MISSING: error: '[[FILE]]': part 'FKE3' not found
+# CHECK-BAD-PATH: error: '[[FILE]]': [[MSG]]
+
+--- !dxcontainer
+Header:
+  Hash:        [ 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
+                 0x0, 0x0, 0x0, 0x0, 0x0, 0x0 ]
+  Version:
+    Major:     1
+    Minor:     0
+  FileSize:    108
+  PartCount:   3
+  PartOffsets: [ 60, 68, 76 ]
+Parts:
+  - Name: FKE0
+    Size: 0
+  - Name: FKE1
+    Size: 0
+  - Name: FKE2
+    Size: 8
+...