Revert r270977 ([llvm-mc] - Teach llvm-mc to generate zlib styled compression sections.)

It broke buildbot:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/builds/13585/steps/build/logs/stdio

Initial commit message:
[llvm-mc] - Teach llvm-mc to generate zlib styled compression sections.

This patch is strongly based on previously reverted D20331.
(because of gnuutils < 2.26 does not support compressed debug sections in non zlib-gnu style)

Difference that this patch supports both zlib and zlib-gnu styles.

-compress-debug-sections option now supports next values:

-compress-debug-sections=zlib-gnu
-compress-debug-sections=zlib
-compress-debug-sections=none
Previously specifying -compress-debug-sections enabled zlib-gnu compression,
so anyone can put "-compress-debug-sections=zlib-gnu" to restore the behavior
that was before this patch for case when compression was enabled.

Differential revision: http://reviews.llvm.org/D20676

llvm-svn: 270978

1 files changed, 19 insertions, 50 deletions

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 4f1b370..900dcf5 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -136,10 +136,6 @@ class ELFObjectWriter : public MCObjectWriter {
 
   void align(unsigned Alignment);
 
-  bool maybeWriteCompression(uint64_t Size,
-                             SmallVectorImpl<char> &CompressedContents,
-                             bool ZLibStyle, unsigned Alignment);
-
 public:
   ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
                   bool IsLittleEndian)
@@ -983,38 +979,23 @@ ELFObjectWriter::createRelocationSection(MCContext &Ctx,
   return RelaSection;
 }
 
-// Include the debug info compression header.
-bool ELFObjectWriter::maybeWriteCompression(
-    uint64_t Size, SmallVectorImpl<char> &CompressedContents, bool ZLibStyle,
-    unsigned Alignment) {
-  if (ZLibStyle) {
-    uint64_t HdrSize =
-        is64Bit() ? sizeof(ELF::Elf32_Chdr) : sizeof(ELF::Elf64_Chdr);
-    if (Size <= HdrSize + CompressedContents.size())
-      return false;
-    // Platform specific header is followed by compressed data.
-    if (is64Bit()) {
-      // Write Elf64_Chdr header.
-      write(static_cast<ELF::Elf64_Word>(ELF::ELFCOMPRESS_ZLIB));
-      write(static_cast<ELF::Elf64_Word>(0)); // ch_reserved field.
-      write(static_cast<ELF::Elf64_Xword>(Size));
-      write(static_cast<ELF::Elf64_Xword>(Alignment));
-    } else {
-      // Write Elf32_Chdr header otherwise.
-      write(static_cast<ELF::Elf32_Word>(ELF::ELFCOMPRESS_ZLIB));
-      write(static_cast<ELF::Elf32_Word>(Size));
-      write(static_cast<ELF::Elf32_Word>(Alignment));
-    }
-    return true;
-  }
-
-  // "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
-  // useful for consumers to preallocate a buffer to decompress into.
+// Include the debug info compression header:
+// "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
+// useful for consumers to preallocate a buffer to decompress into.
+static bool
+prependCompressionHeader(uint64_t Size,
+                         SmallVectorImpl<char> &CompressedContents) {
   const StringRef Magic = "ZLIB";
   if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
     return false;
-  write(ArrayRef<char>(Magic.begin(), Magic.size()));
-  writeBE64(Size);
+  if (sys::IsLittleEndianHost)
+    sys::swapByteOrder(Size);
+  CompressedContents.insert(CompressedContents.begin(),
+                            Magic.size() + sizeof(Size), 0);
+  std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
+  std::copy(reinterpret_cast<char *>(&Size),
+            reinterpret_cast<char *>(&Size + 1),
+            CompressedContents.begin() + Magic.size());
   return true;
 }
 
@@ -1026,11 +1007,8 @@ void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
   // Compressing debug_frame requires handling alignment fragments which is
   // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
   // for writing to arbitrary buffers) for little benefit.
-  bool CompressionEnabled =
-      Asm.getContext().getAsmInfo()->compressDebugSections() !=
-      DebugCompressionType::DCT_None;
-  if (!CompressionEnabled || !SectionName.startswith(".debug_") ||
-      SectionName == ".debug_frame") {
+  if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
+      !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
     Asm.writeSectionData(&Section, Layout);
     return;
   }
@@ -1051,21 +1029,12 @@ void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
     return;
   }
 
-  bool ZlibStyle = Asm.getContext().getAsmInfo()->compressDebugSections() ==
-                   DebugCompressionType::DCT_Zlib;
-  if (!maybeWriteCompression(UncompressedData.size(), CompressedContents,
-                             ZlibStyle, Sec.getAlignment())) {
+  if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
     getStream() << UncompressedData;
     return;
   }
-
-  if (ZlibStyle)
-    // Set the compressed flag. That is zlib style.
-    Section.setFlags(Section.getFlags() | ELF::SHF_COMPRESSED);
-  else
-    // Add "z" prefix to section name. This is zlib-gnu style.
-    Asm.getContext().renameELFSection(&Section,
-                                      (".z" + SectionName.drop_front(1)).str());
+  Asm.getContext().renameELFSection(&Section,
+                                    (".z" + SectionName.drop_front(1)).str());
   getStream() << CompressedContents;
 }