[llvm-objcopy] --[de]compress-debug-sections: don't compress SHF_ALLOC sections, only decompress .debug sections

llvm/lib/ObjCopy/ELF/ELFObjcopy.cpp

@@ -214,33 +214,32 @@ static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
                            SecName.str().c_str());
 }
 
-static bool isCompressable(const SectionBase &Sec) {
-  return !(Sec.Flags & ELF::SHF_COMPRESSED) &&
-         StringRef(Sec.Name).starts_with(".debug");
-}
-
-static Error replaceDebugSections(
-    Object &Obj, function_ref<bool(const SectionBase &)> ShouldReplace,
-    function_ref<Expected<SectionBase *>(const SectionBase *)> AddSection) {
+Error Object::compressOrDecompressSections(const CommonConfig &Config) {
   // Build a list of the debug sections we are going to replace.
   // We can't call `AddSection` while iterating over sections,
   // because it would mutate the sections array.
-  SmallVector<SectionBase *, 13> ToReplace;
-  for (auto &Sec : Obj.sections())
-    if (ShouldReplace(Sec))
-      ToReplace.push_back(&Sec);
-
-  // Build a mapping from original section to a new one.
-  DenseMap<SectionBase *, SectionBase *> FromTo;
-  for (SectionBase *S : ToReplace) {
-    Expected<SectionBase *> NewSection = AddSection(S);
-    if (!NewSection)
-      return NewSection.takeError();
-
-    FromTo[S] = *NewSection;
+  SmallVector<std::pair<SectionBase *, std::function<SectionBase *()>>, 0>
+      ToReplace;
+  for (SectionBase &Sec : sections()) {
+    if ((Sec.Flags & SHF_ALLOC) || !StringRef(Sec.Name).starts_with(".debug"))
+      continue;
+    if (auto *CS = dyn_cast<CompressedSection>(&Sec)) {
+      if (Config.DecompressDebugSections) {
+        ToReplace.emplace_back(
+            &Sec, [=] { return &addSection<DecompressedSection>(*CS); });
+      }
+    } else if (Config.CompressionType != DebugCompressionType::None) {
+      ToReplace.emplace_back(&Sec, [&, S = &Sec] {
+        return &addSection<CompressedSection>(
+            CompressedSection(*S, Config.CompressionType, Is64Bits));
+      });
+    }
   }
 
-  return Obj.replaceSections(FromTo);
+  DenseMap<SectionBase *, SectionBase *> FromTo;
+  for (auto [S, Func] : ToReplace)
+    FromTo[S] = Func();
+  return replaceSections(FromTo);
 }
 
 static bool isAArch64MappingSymbol(const Symbol &Sym) {
@@ -534,24 +533,8 @@ static Error replaceAndRemoveSections(const CommonConfig &Config,
   if (Error E = Obj.removeSections(ELFConfig.AllowBrokenLinks, RemovePred))
     return E;
 
-  if (Config.CompressionType != DebugCompressionType::None) {
-    if (Error Err = replaceDebugSections(
-            Obj, isCompressable,
-            [&Config, &Obj](const SectionBase *S) -> Expected<SectionBase *> {
-              return &Obj.addSection<CompressedSection>(
-                  CompressedSection(*S, Config.CompressionType, Obj.Is64Bits));
-            }))
-      return Err;
-  } else if (Config.DecompressDebugSections) {
-    if (Error Err = replaceDebugSections(
-            Obj,
-            [](const SectionBase &S) { return isa<CompressedSection>(&S); },
-            [&Obj](const SectionBase *S) {
-              const CompressedSection *CS = cast<CompressedSection>(S);
-              return &Obj.addSection<DecompressedSection>(*CS);
-            }))
-      return Err;
-  }
+  if (Error E = Obj.compressOrDecompressSections(Config))
+    return E;
 
   return Error::success();
 }

llvm/lib/ObjCopy/ELF/ELFObject.h

@@ -1210,6 +1210,7 @@ class Object {
 
   Error removeSections(bool AllowBrokenLinks,
                        std::function<bool(const SectionBase &)> ToRemove);
+  Error compressOrDecompressSections(const CommonConfig &Config);
   Error replaceSections(const DenseMap<SectionBase *, SectionBase *> &FromTo);
   Error removeSymbols(function_ref<bool(const Symbol &)> ToRemove);
   template <class T, class... Ts> T &addSection(Ts &&...Args) {

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

@@ -43,6 +43,10 @@ Sections:
     Type:            SHT_PROGBITS
     Flags:           [ SHF_GROUP ]
     Content:         '00'
+  - Name:            .debug_alloc
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    Content:         000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f000102030405060708090a0b0c0d0e0f
 Symbols:
   - Type:    STT_SECTION
     Section: .debug_foo

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

@@ -12,8 +12,10 @@
 # CHECK:             Name              Type            Address          Off    Size   ES Flg Lk Inf Al
 # COMPRESSED:        .debug_foo        PROGBITS        0000000000000000 000040 {{.*}} 00   C  0   0  8
 # COMPRESSED-NEXT:   .notdebug_foo     PROGBITS        0000000000000000 {{.*}} 000008 00      0   0  0
+# COMPRESSED:        .debug_alloc      PROGBITS        0000000000000000 {{.*}} 000040 00   A  0   0  0
 # UNCOMPRESSED:      .debug_foo        PROGBITS        0000000000000000 000040 000008 00      0   0  0
 # UNCOMPRESSED-NEXT: .notdebug_foo     PROGBITS        0000000000000000 {{.*}} 000008 00      0   0  0
+# UNCOMPRESSED:      .debug_alloc      PROGBITS        0000000000000000 {{.*}} 000040 00   A  0   0  0
 
 ## Relocations do not change.
 # CHECK:             Relocation section '.rela.debug_foo' at offset {{.*}} contains 2 entries:

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

@@ -12,8 +12,10 @@
 # CHECK:             Name              Type            Address          Off    Size   ES Flg Lk Inf Al
 # COMPRESSED:        .debug_foo        PROGBITS        0000000000000000 000040 {{.*}} 00   C  0   0  8
 # COMPRESSED-NEXT:   .notdebug_foo     PROGBITS        0000000000000000 {{.*}} 000008 00      0   0  0
+# COMPRESSED:        .debug_alloc      PROGBITS        0000000000000000 {{.*}} 000040 00   A  0   0  0
 # DECOMPRESSED:      .debug_foo        PROGBITS        0000000000000000 000040 000008 00      0   0  0
 # DECOMPRESSED-NEXT: .notdebug_foo     PROGBITS        0000000000000000 {{.*}} 000008 00      0   0  0
+# DECOMPRESSED:      .debug_alloc      PROGBITS        0000000000000000 {{.*}} 000040 00   A  0   0  0
 
 ## Relocations do not change.
 # CHECK:             Relocation section '.rela.debug_foo' at offset {{.*}} contains 2 entries:

llvm/test/tools/llvm-objcopy/ELF/decompress-sections.test

@@ -0,0 +1,36 @@
+# REQUIRES: zlib
+## Test decompression for different sections.
+
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-objcopy --decompress-debug-sections %t %t.de
+# RUN: llvm-readelf -S %t.de | FileCheck %s
+
+# CHECK:        Name              Type            Address          Off      Size     ES Flg Lk Inf Al
+# CHECK:        .debug_alloc      PROGBITS        0000000000000000 [[#%x,]] [[#%x,]] 00  AC  0   0  0
+# CHECK-NEXT:   .debug_nonalloc   PROGBITS        0000000000000000 [[#%x,]] [[#%x,]] 00      0   0  1
+# CHECK-NEXT:   .debugx           PROGBITS        0000000000000000 [[#%x,]] [[#%x,]] 00      0   0  1
+# CHECK-NEXT:   nodebug           PROGBITS        0000000000000000 [[#%x,]] [[#%x,]] 00   C  0   0  0
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:      .debug_alloc
+    Type:      SHT_PROGBITS
+    Flags:     [ SHF_ALLOC, SHF_COMPRESSED ]
+    Content:   010000000000000040000000000000000100000000000000789cd36280002d3269002f800151
+  - Name:      .debug_nonalloc
+    Type:      SHT_PROGBITS
+    Flags:     [ SHF_COMPRESSED ]
+    Content:   010000000000000040000000000000000100000000000000789cd36280002d3269002f800151
+  - Name:      .debugx
+    Type:      SHT_PROGBITS
+    Flags:     [ SHF_COMPRESSED ]
+    Content:   010000000000000040000000000000000100000000000000789cd36280002d3269002f800151
+  - Name:      nodebug
+    Type:      SHT_PROGBITS
+    Flags:     [ SHF_COMPRESSED ]
+    Content:   010000000000000040000000000000000100000000000000789cd36280002d3269002f800151