[llvm-objcopy] Remove support for legacy .zdebug sections

clang 14 removed -gz=zlib-gnu support and ld.lld removed linker input support
for zlib-gnu in D126793. Now let's remove zlib-gnu from llvm-objcopy.

* .zdebug* sections are no longer recognized as debug sections. --strip* don't remove them.
  They are copied like other opaque sections
* --decompress-debug-sections does not uncompress .zdebug* sections
* --compress-debug-sections=zlib-gnu is not supported

It is very rare but in case a user has object files using .zdebug . They can use
llvm-objcopy<15 or GNU objcopy for uncompression.
--compress-debug-sections=zlib-gnu is unlikely ever used by anyone, so I do not
add a custom diagnostic.

Differential Revision: https://reviews.llvm.org/D128688

llvm/docs/ReleaseNotes.rst

@@ -204,6 +204,7 @@ Changes to the LLVM tools
 * (Experimental) :manpage:`llvm-symbolizer(1)` now has ``--filter-markup`` to
   filter :doc:`Symbolizer Markup </SymbolizerMarkupFormat>` into human-readable
   form.
+* :doc:`llvm-objcopy <CommandGuide/llvm-objcopy>` has removed support for the legacy ``zlib-gnu`` format.
 
 Changes to LLDB
 ---------------------------------

llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp

@@ -53,8 +53,7 @@ using namespace llvm::object;
 using SectionPred = std::function<bool(const SectionBase &Sec)>;
 
 static bool isDebugSection(const SectionBase &Sec) {
-  return StringRef(Sec.Name).startswith(".debug") ||
-         StringRef(Sec.Name).startswith(".zdebug") || Sec.Name == ".gdb_index";
+  return StringRef(Sec.Name).startswith(".debug") || Sec.Name == ".gdb_index";
 }
 
 static bool isDWOSection(const SectionBase &Sec) {

llvm/lib/ObjCopy/ELF/ELFObject.cpp

@@ -519,27 +519,22 @@ Error BinarySectionWriter::visit(const CompressedSection &Sec) {
 template <class ELFT>
 Error ELFSectionWriter<ELFT>::visit(const CompressedSection &Sec) {
   uint8_t *Buf = reinterpret_cast<uint8_t *>(Out.getBufferStart()) + Sec.Offset;
-  if (Sec.CompressionType == DebugCompressionType::None) {
+  Elf_Chdr_Impl<ELFT> Chdr;
+  switch (Sec.CompressionType) {
+  case DebugCompressionType::None:
     std::copy(Sec.OriginalData.begin(), Sec.OriginalData.end(), Buf);
     return Error::success();
-  }
-
-  if (Sec.CompressionType == DebugCompressionType::GNU) {
-    const char *Magic = "ZLIB";
-    memcpy(Buf, Magic, strlen(Magic));
-    Buf += strlen(Magic);
-    const uint64_t DecompressedSize =
-        support::endian::read64be(&Sec.DecompressedSize);
-    memcpy(Buf, &DecompressedSize, sizeof(DecompressedSize));
-    Buf += sizeof(DecompressedSize);
-  } else {
-    Elf_Chdr_Impl<ELFT> Chdr;
+  case DebugCompressionType::GNU:
+    llvm_unreachable("unexpected zlib-gnu");
+    break;
+  case DebugCompressionType::Z:
     Chdr.ch_type = ELF::ELFCOMPRESS_ZLIB;
-    Chdr.ch_size = Sec.DecompressedSize;
-    Chdr.ch_addralign = Sec.DecompressedAlign;
-    memcpy(Buf, &Chdr, sizeof(Chdr));
-    Buf += sizeof(Chdr);
+    break;
   }
+  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);
   return Error::success();
@@ -553,18 +548,13 @@ CompressedSection::CompressedSection(const SectionBase &Sec,
                            OriginalData.size()),
                  CompressedData);
 
-  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>)));
-  }
+  assert(CompressionType != DebugCompressionType::None);
+  Flags |= ELF::SHF_COMPRESSED;
+  size_t 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;
 }

llvm/lib/ObjCopy/ELF/ELFObject.h

@@ -554,8 +554,7 @@ class CompressedSection : public SectionBase {
   Error accept(MutableSectionVisitor &Visitor) override;
 
   static bool classof(const SectionBase *S) {
-    return (S->OriginalFlags & ELF::SHF_COMPRESSED) ||
-           (StringRef(S->Name).startswith(".zdebug"));
+    return S->OriginalFlags & ELF::SHF_COMPRESSED;
   }
 };
 
@@ -568,8 +567,6 @@ class DecompressedSection : public SectionBase {
     Size = Sec.getDecompressedSize();
     Align = Sec.getDecompressedAlign();
     Flags = OriginalFlags = (Flags & ~ELF::SHF_COMPRESSED);
-    if (StringRef(Name).startswith(".zdebug"))
-      Name = "." + Name.substr(2);
   }
 
   Error accept(SectionVisitor &Visitor) const override;

llvm/test/tools/llvm-objcopy/ELF/compress-debug-sections-groups.test

@@ -10,27 +10,11 @@
 # RUN: llvm-readobj -S --section-groups %t-compressed.o | \
 # RUN:   FileCheck %s --check-prefixes=CHECK,COMPRESS
 
-## Check zlib-gnu compression of debug sections.
-# RUN: llvm-objcopy --compress-debug-sections=zlib-gnu %t.o %t-compressed-gnu.o
-# RUN: llvm-readobj -S --section-groups %t-compressed-gnu.o | \
-# RUN:   FileCheck %s --check-prefixes=CHECK,COMPRESSZLIB
-
 ## Check decompression of debug sections.
 # RUN: llvm-objcopy --decompress-debug-sections %t-compressed.o %t-decompressed.o
 # RUN: llvm-readobj --section-groups %t-decompressed.o | \
 # RUN:   FileCheck %s --check-prefixes=CHECK,DECOMPRESS
 
-## Check decompression of zlib-gnu debug sections.
-# RUN: llvm-objcopy --decompress-debug-sections %t-compressed-gnu.o %t-decompressed-gnu.o
-# RUN: llvm-readobj --section-groups %t-decompressed-gnu.o | \
-# RUN:   FileCheck %s --check-prefixes=CHECK,DECOMPRESS
-
-# COMPRESSZLIB:      Name: .zdebug_in_group
-# COMPRESSZLIB-NEXT: Type: SHT_PROGBITS
-# COMPRESSZLIB-NEXT: Flags [
-# COMPRESSZLIB-NEXT:   SHF_GROUP
-# COMPRESSZLIB-NEXT: ]
-
 # COMPRESS:      Name: .debug_in_group
 # COMPRESS-NEXT: Type: SHT_PROGBITS
 # COMPRESS-NEXT: Flags [
@@ -47,7 +31,6 @@
 # CHECK-NEXT:        Signature: groupname
 # CHECK-NEXT:        Section(s) in group [
 # CHECK-NEXT:          .text.in.group
-# COMPRESSZLIB-NEXT:   .zdebug_in_group
 # COMPRESS-NEXT:       .debug_in_group
 # DECOMPRESS-NEXT:     .debug_in_group
 # CHECK-NEXT:        ]

llvm/test/tools/llvm-objcopy/ELF/compress-debug-sections-invalid-format.test

@@ -1,5 +1,6 @@
 # RUN: yaml2obj %p/Inputs/compress-debug-sections.yaml -o %t.o
 # RUN: not llvm-objcopy --compress-debug-sections=zlib-fake %t.o 2>&1 | FileCheck %s
+# RUN: not llvm-objcopy --compress-debug-sections=zlib-gnu %t.o 2>&1 | FileCheck %s --check-prefix=GNU
 
 # CHECK: invalid or unsupported --compress-debug-sections format: zlib-fake
-
+# GNU:   invalid or unsupported --compress-debug-sections format: zlib-gnu

llvm/test/tools/llvm-objcopy/ELF/compress-debug-sections-symbols.test

@@ -6,16 +6,12 @@
 ## and it is placed into the right section.
 
 # RUN: llvm-objcopy --compress-debug-sections %t.o %t-compressed1.o
-# RUN: llvm-readobj --symbols %t-compressed1.o | FileCheck %s --check-prefixes=CHECK,ZLIB
-
-# RUN: llvm-objcopy --compress-debug-sections=zlib-gnu %t.o %t-compressed2.o
-# RUN: llvm-readobj --symbols %t-compressed2.o | FileCheck %s --check-prefixes=CHECK,ZLIBGNU
+# RUN: llvm-readobj --symbols %t-compressed1.o | FileCheck %s
 
 # CHECK:        Name:    .Linfo_string0
 # CHECK-NEXT:   Value:   0x0
 # CHECK-NEXT:   Size:    0
 # CHECK-NEXT:   Binding: Global
 # CHECK-NEXT:   Type:    None
 # CHECK-NEXT:   Other:   0
-# ZLIB-NEXT:    Section: .debug_bar
-# ZLIBGNU-NEXT: Section: .zdebug_bar
+# CHECK-NEXT:   Section: .debug_bar

llvm/test/tools/llvm-objcopy/ELF/compress-debug-sections.test

@@ -4,21 +4,15 @@
 # RUN: cp %t.o %t.copy.o
 
 # RUN: llvm-objcopy --compress-debug-sections=zlib     %t.o %tz.o
-# RUN: llvm-objcopy --compress-debug-sections=zlib-gnu %t.o %tzg.o
 # RUN: cp %tz.o %tz.copy.o
-# RUN: cp %tzg.o %tzg.copy.o
 
 # RUN: llvm-objcopy --decompress-debug-sections %tz.o  %t2.o
-# RUN: llvm-objcopy --decompress-debug-sections %tzg.o %t3.o
 
 # Using redirects to avoid llvm-objdump from printing the filename.
 # RUN: llvm-objdump -s --section=.debug_str - < %t.o  > %t.txt
 # RUN: llvm-objdump -s --section=.debug_str - < %t2.o > %t2.txt
-# RUN: llvm-objdump -s --section=.debug_str - < %t3.o > %t3.txt
 
 # RUN: diff %t.txt %t2.txt
-# RUN: diff %t.txt %t3.txt
 
 # RUN: cmp %t.o %t.copy.o
 # RUN: cmp %tz.o %tz.copy.o
-# RUN: cmp %tzg.o %tzg.copy.o

llvm/test/tools/llvm-objcopy/ELF/strip-debug.test

@@ -98,6 +98,7 @@ Sections:
   - Name:            .debugfoo
     Type:            SHT_PROGBITS
     Content:         "00000000"
+  ## .zdebug is no longer recognized as a debug section.
   - Name:            .zdebugfoo
     Type:            SHT_PROGBITS
     Content:         "00000000"
@@ -119,8 +120,9 @@ Symbols:
   - Name:    filesymbol
     Type:    STT_FILE
 
-# CHECK: SectionHeaderCount: 5
+# CHECK: SectionHeaderCount: 6
 
+# CHECK: Name: .zdebugfoo
 # CHECK: Name: .text
 # CHECK: Name: .symtab
 # CHECK: Name: .strtab

llvm/test/tools/llvm-objcopy/ELF/zdebug.yaml

@@ -0,0 +1,24 @@
+## .zdebug is no longer recognized as zlib-gnu compressed sections. It's treated
+## as an opaque non-debug section.
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objcopy --decompress-debug-sections %t %t.copy
+# RUN: llvm-readelf -S %t.copy | FileCheck %s
+
+# CHECK: .zdebug_str
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:         .text
+    Type:         SHT_PROGBITS
+    Flags:        [ SHF_ALLOC, SHF_EXECINSTR ]
+    Content:      '00'
+  - Name:         .zdebug_str
+    Type:         SHT_PROGBITS
+    Content:      5a4c49420000000000000002789c4b64000000c40062
+    AddressAlign: 8
+...

llvm/tools/llvm-objcopy/ObjcopyOptions.cpp

@@ -729,7 +729,6 @@ objcopy::parseObjcopyOptions(ArrayRef<const char *> RawArgsArr,
       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)

llvm/tools/llvm-objcopy/ObjcopyOpts.td

@@ -32,9 +32,9 @@ defm new_symbol_visibility : Eq<"new-symbol-visibility", "Visibility of "
 def compress_debug_sections : Flag<["--"], "compress-debug-sections">;
 def compress_debug_sections_eq
     : Joined<["--"], "compress-debug-sections=">,
-      MetaVarName<"[ zlib | zlib-gnu ]">,
+      MetaVarName<"[ zlib ]">,
       HelpText<"Compress DWARF debug sections using specified style. Supported "
-               "styles: 'zlib-gnu' and 'zlib'">;
+               "formats: 'zlib'">;
 def decompress_debug_sections : Flag<["--"], "decompress-debug-sections">,
                                 HelpText<"Decompress DWARF debug sections.">;
 defm split_dwo