[llvm-objcopy] Dwarf .debug section compression support (zlib, zlib-gnu).

  Second Attempt. Alignment issues resolved. zlib::isAvailable() detected.

  Usage:

  llvm-objcopy --compress-debug-sections=zlib foo.o
  llvm-objcopy --compress-debug-sections=zlib-gnu foo.o

  In both cases the debug section contents is compressed with zlib. In the GNU
  style case the header is the "ZLIB" magic string followed by the uint64 big-
  endian decompressed size. In the non-GNU mode the header is the
  Elf(32|64)_Chdr.

  Decompression support is coming soon.

  Differential Revision: https://reviews.llvm.org/D49678

llvm-svn: 341607

1 files changed, 72 insertions, 0 deletions

diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
index 2ff24ce9a25..fcdf2a4bcb2 100644
--- a/llvm/tools/llvm-objcopy/Object.cpp
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -15,7 +15,9 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCTargetOptions.h"
 #include "llvm/Object/ELFObjectFile.h"
+#include "llvm/Support/Compression.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileOutputBuffer.h"
 #include "llvm/Support/Path.h"
@@ -138,6 +140,76 @@ void OwnedDataSection::accept(SectionVisitor &Visitor) const {
   Visitor.visit(*this);
 }
 
+void BinarySectionWriter::visit(const CompressedSection &Sec) {
+  error("Cannot write compressed section '" + Sec.Name + "' ");
+}
+
+template <class ELFT>
+void ELFSectionWriter<ELFT>::visit(const CompressedSection &Sec) {
+  uint8_t *Buf = Out.getBufferStart();
+  Buf += Sec.Offset;
+
+  if (Sec.CompressionType == DebugCompressionType::None) {
+    std::copy(Sec.OriginalData.begin(), Sec.OriginalData.end(), Buf);
+    return;
+  }
+
+  if (Sec.CompressionType == DebugCompressionType::GNU) {
+    ArrayRef<uint8_t> Magic = {'Z', 'L', 'I', 'B'};
+    std::copy(Magic.begin(), Magic.end(), Buf);
+    Buf += Magic.size();
+    const uint64_t DecompressedSize =
+        support::endian::read64be(&Sec.DecompressedSize);
+    memcpy(Buf, &DecompressedSize, sizeof(DecompressedSize));
+    Buf += sizeof(DecompressedSize);
+  } else {
+    Elf_Chdr_Impl<ELFT> Chdr;
+    Chdr.ch_type = ELF::ELFCOMPRESS_ZLIB;
+    Chdr.ch_size = Sec.DecompressedSize;
+    Chdr.ch_addralign = Sec.DecompressedAlign;
+    memcpy(Buf, &Chdr, sizeof(Chdr));
+    Buf += sizeof(Chdr);
+  }
+
+  std::copy(Sec.CompressedData.begin(), Sec.CompressedData.end(), Buf);
+}
+
+CompressedSection::CompressedSection(const SectionBase &Sec,
+                                     DebugCompressionType CompressionType)
+    : SectionBase(Sec), CompressionType(CompressionType),
+      DecompressedSize(Sec.OriginalData.size()), DecompressedAlign(Sec.Align) {
+
+  if (!zlib::isAvailable()) {
+    CompressionType = DebugCompressionType::None;
+    return;
+  }
+
+  if (Error E = zlib::compress(
+          StringRef(reinterpret_cast<const char *>(OriginalData.data()),
+                    OriginalData.size()),
+          CompressedData))
+    reportError(Name, std::move(E));
+
+  size_t ChdrSize;
+  if (CompressionType == DebugCompressionType::GNU) {
+    Name = ".z" + Sec.Name.substr(1);
+    ChdrSize = sizeof("ZLIB") - 1 + sizeof(uint64_t);
+  } else {
+    Flags |= ELF::SHF_COMPRESSED;
+    ChdrSize =
+        std::max(std::max(sizeof(object::Elf_Chdr_Impl<object::ELF64LE>),
+                          sizeof(object::Elf_Chdr_Impl<object::ELF64BE>)),
+                 std::max(sizeof(object::Elf_Chdr_Impl<object::ELF32LE>),
+                          sizeof(object::Elf_Chdr_Impl<object::ELF32BE>)));
+  }
+  Size = ChdrSize + CompressedData.size();
+  Align = 8;
+}
+
+void CompressedSection::accept(SectionVisitor &Visitor) const {
+  Visitor.visit(*this);
+}
+
 void StringTableSection::addString(StringRef Name) {
   StrTabBuilder.add(Name);
   Size = StrTabBuilder.getSize();