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

  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: 341342

1 files changed, 69 insertions, 4 deletions

diff --git a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
index 72501f3..f0d6b44 100644
--- a/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
+++ b/llvm/tools/llvm-objcopy/llvm-objcopy.cpp
@@ -17,6 +17,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCTargetOptions.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ArchiveWriter.h"
 #include "llvm/Object/Binary.h"
@@ -175,6 +176,7 @@ struct CopyConfig {
   bool StripSections = false;
   bool StripUnneeded = false;
   bool Weaken = false;
+  DebugCompressionType CompressionType = DebugCompressionType::None;
 };
 
 using SectionPred = std::function<bool(const SectionBase &Sec)>;
@@ -290,12 +292,12 @@ static SectionRename parseRenameSectionValue(StringRef FlagValue) {
 }
 
 static bool isDebugSection(const SectionBase &Sec) {
-  return Sec.Name.startswith(".debug") || Sec.Name.startswith(".zdebug") ||
-         Sec.Name == ".gdb_index";
+  return StringRef(Sec.Name).startswith(".debug") ||
+         StringRef(Sec.Name).startswith(".zdebug") || Sec.Name == ".gdb_index";
 }
 
 static bool isDWOSection(const SectionBase &Sec) {
-  return Sec.Name.endswith(".dwo");
+  return StringRef(Sec.Name).endswith(".dwo");
 }
 
 static bool onlyKeepDWOPred(const Object &Obj, const SectionBase &Sec) {
@@ -405,6 +407,49 @@ static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
                                  object_error::parse_failed);
 }
 
+static bool isCompressed(const SectionBase &Section) {
+  ArrayRef<uint8_t> GnuPrefix = {'Z', 'L', 'I', 'B'};
+  return StringRef(Section.Name).startswith(".zdebug") ||
+         (Section.OriginalData.size() > strlen("ZLIB") &&
+          std::equal(GnuPrefix.begin(), GnuPrefix.end(),
+                     Section.OriginalData.data())) ||
+         (Section.Flags & ELF::SHF_COMPRESSED);
+}
+
+static bool isCompressable(const SectionBase &Section) {
+  return !isCompressed(Section) && isDebugSection(Section) &&
+         Section.Name != ".gdb_index";
+}
+
+static void compressSections(const CopyConfig &Config, Object &Obj,
+                             SectionPred &RemovePred) {
+  SmallVector<SectionBase *, 13> ToCompress;
+  SmallVector<RelocationSection *, 13> RelocationSections;
+  for (auto &Sec : Obj.sections()) {
+    if (RelocationSection *R = dyn_cast<RelocationSection>(&Sec)) {
+      if (isCompressable(*R->getSection()))
+        RelocationSections.push_back(R);
+      continue;
+    }
+
+    if (isCompressable(Sec))
+      ToCompress.push_back(&Sec);
+  }
+
+  for (SectionBase *S : ToCompress) {
+    CompressedSection &CS =
+        Obj.addSection<CompressedSection>(*S, Config.CompressionType);
+
+    for (RelocationSection *RS : RelocationSections) {
+      if (RS->getSection() == S)
+        RS->setSection(&CS);
+    }
+  }
+
+  RemovePred = [RemovePred](const SectionBase &Sec) {
+    return isCompressable(Sec) || RemovePred(Sec);
+  };
+}
 // This function handles the high level operations of GNU objcopy including
 // handling command line options. It's important to outline certain properties
 // we expect to hold of the command line operations. Any operation that "keeps"
@@ -564,7 +609,7 @@ static void handleArgs(const CopyConfig &Config, Object &Obj,
         return true;
       if (&Sec == Obj.SectionNames)
         return false;
-      if (Sec.Name.startswith(".gnu.warning"))
+      if (StringRef(Sec.Name).startswith(".gnu.warning"))
         return false;
       return (Sec.Flags & SHF_ALLOC) == 0;
     };
@@ -616,6 +661,9 @@ static void handleArgs(const CopyConfig &Config, Object &Obj,
     };
   }
 
+  if (Config.CompressionType != DebugCompressionType::None)
+    compressSections(Config, Obj, RemovePred);
+
   Obj.removeSections(RemovePred);
 
   if (!Config.SectionsToRename.empty()) {
@@ -860,6 +908,23 @@ static CopyConfig parseObjcopyOptions(ArrayRef<const char *> ArgsArr) {
     Config.BinaryArch = getMachineInfo(BinaryArch);
   }
 
+  if (auto Arg = InputArgs.getLastArg(OBJCOPY_compress_debug_sections,
+                                      OBJCOPY_compress_debug_sections_eq)) {
+    Config.CompressionType = DebugCompressionType::Z;
+
+    if (Arg->getOption().getID() == OBJCOPY_compress_debug_sections_eq) {
+      Config.CompressionType =
+          StringSwitch<DebugCompressionType>(
+              InputArgs.getLastArgValue(OBJCOPY_compress_debug_sections_eq))
+              .Case("zlib-gnu", DebugCompressionType::GNU)
+              .Case("zlib", DebugCompressionType::Z)
+              .Default(DebugCompressionType::None);
+      if (Config.CompressionType == DebugCompressionType::None)
+        error("Invalid or unsupported --compress-debug-sections format: " +
+              InputArgs.getLastArgValue(OBJCOPY_compress_debug_sections_eq));
+    }
+  }
+
   Config.SplitDWO = InputArgs.getLastArgValue(OBJCOPY_split_dwo);
   Config.AddGnuDebugLink = InputArgs.getLastArgValue(OBJCOPY_add_gnu_debuglink);
   Config.SymbolsPrefix = InputArgs.getLastArgValue(OBJCOPY_prefix_symbols);