[llvm-objcopy][MachO] Implement --dump-section

[jhenderson]

llvm/test/tools/llvm-objcopy/MachO/dump-section.test

12

Nit: nonexistent -> non-existent

17

It probably makes more sense to put the positive cases before the negative ones.

[seiya]

Fixed review comments.

[alexander-shaposhnikov]

LG!

[jhenderson]

LGTM too (though I've not tried to look too hard at the Mach-O code).

[MaskRay]

llvm/test/tools/llvm-objcopy/MachO/dump-section.test

65

It seems reserved3 is optional but reserved[12] are not:

// lib/ObjectYAML/MachOYAML.cpp#L279
  IO.mapRequired("reserved1", Section.reserved1);
  IO.mapRequired("reserved2", Section.reserved2);
  IO.mapOptional("reserved3", Section.reserved3);

If some field are not significant in the test, they can be deleted.

[seiya]

Update CommandGuide.

[jhenderson]

llvm/docs/CommandGuide/llvm-objcopy.rst

69

remove "the" before "<section>".

[seiya]

Addressed review comments.

llvm/test/tools/llvm-objcopy/MachO/dump-section.test

65

Oh I didn't noticed that. Thanks.

[seiya]

CommandGuide: Removed remove "the" before "<section>".

[rupprecht]

llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp

110–111

llvm::copy(Sec.Content, Buf->getBufferStart())

[seiya]

Rebased. NFCI.

[seiya]

I'll commit this patch on next Monday.

[MaskRay]

llvm/test/tools/llvm-objcopy/MachO/dump-section.test

5

-o (it seems -o is more common. I prefer it because it avoids a shell redirection)

[seiya]

Addressed a comment.

llvm/docs/CommandGuide/llvm-objcopy.rst

  headers.
 
 .. option:: --discard-all, -x
 
  Remove most local symbols from the output. Different file formats may limit
  this to a subset of the local symbols. For example, file and section symbols in
  ELF objects will not be discarded.
 
+.. option:: --dump-section <section>=<file>
+
+ Dump the contents of section ``<section>`` into the file ``<file>``. Can be
+ specified multiple times to dump multiple sections to different files.
+ ``<file>`` is unrelated to the input and output files provided to
+ :program:`llvm-objcopy` and as such the normal copying and editing
+ operations will still be performed. No operations are performed on the sections
+ prior to dumping them.
+
+ For MachO objects, the ``<section>`` must be formatted as
+ ``<segment name>,<section name>``.
+
 .. option:: --enable-deterministic-archives, -D
 
  Enable deterministic mode when copying archives, i.e. use 0 for archive member
  header UIDs, GIDs and timestamp fields. On by default.
 
 .. option:: --help, -h
 
  Print a summary of command line options.

 .. option:: --decompress-debug-sections
 
  Decompress any compressed DWARF debug sections in the output.
 
 .. option:: --discard-locals, -X
 
  Remove local symbols starting with ".L" from the output.
 
-.. option:: --dump-section <section>=<file>
-
- Dump the contents of section ``<section>`` into the file ``<file>``. Can be
- specified multiple times to dump multiple sections to different files.
- ``<file>`` is unrelated to the input and output files provided to
- :program:`llvm-objcopy` and as such the normal copying and editing
- operations will still be performed. No operations are performed on the sections
- prior to dumping them.
-
 .. option:: --extract-dwo
 
  Remove all sections that are not DWARF .dwo sections from the output.
 
 .. option:: --extract-main-partition
 
  Extract the main partition from the output.
 

llvm/test/tools/llvm-objcopy/MachO/dump-section.test

+## Show that llvm-objcopy extracts section contents into files specified by
+## --dump-section.
+
+# RUN: yaml2obj %s > %t
+
+## Extract section contents into files.
+# RUN: llvm-objcopy --dump-section __TEXT,__text=%t.dump.text \
+# RUN:   --dump-section __DATA,__data=%t.dump.data %t
+# RUN: od -t x1 %t.dump.text | FileCheck %s --check-prefix=TEXT-CONTENT
+# RUN: wc -c %t.dump.text | FileCheck %s --check-prefix=TEXT-SIZE
+# RUN: od -t x1 %t.dump.data | FileCheck %s --check-prefix=DATA-CONTENT
+# RUN: wc -c %t.dump.data | FileCheck %s --check-prefix=DATA-SIZE
+
+# TEXT-CONTENT: 0000000 aa bb cc dd
+# TEXT-SIZE: 4
+# DATA-CONTENT: 0000000 ee ff ee ff
+# DATA-SIZE: 4
+
+## Error case 1: An invalid section name.
+# RUN: not llvm-objcopy --dump-section __text=%t.invalid-section-name %t 2>&1 \
+# RUN:   | FileCheck %s -DINPUT=%t --check-prefix=INVALID-SECTION-NAME
+# INVALID-SECTION-NAME: error: '[[INPUT]]': invalid section name '__text' (should be formatted as '<segment name>,<section name>')
+
+## Error case 2: A non-existent section name.
+# RUN: not llvm-objcopy --dump-section __TEXT,__foo=%t.no-such-section %t 2>&1 \
+# RUN:   | FileCheck %s -DINPUT=%t --check-prefix=NO-SUCH-SECTION
+# NO-SUCH-SECTION: error: '[[INPUT]]': section '__TEXT,__foo' not found
+
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x01000007
+  cpusubtype:      0x00000003
+  filetype:        0x00000001
+  ncmds:           1
+  sizeofcmds:      312
+  flags:           0x00002000
+  reserved:        0x00000000
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         312
+    segname:         ''
+    vmaddr:          0
+    vmsize:          12
+    fileoff:         344
+    filesize:        12
+    maxprot:         7
+    initprot:        7
+    nsects:          3
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x0000000000000000
+        content:         'AABBCCDD'
+        size:            4
+        offset:          344
+        align:           0
+        reloff:          0x00000000
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x00000000
+        reserved2:       0x00000000
+      - sectname:        __data
+        segname:         __DATA
+        addr:            0x0000000000000004
+        content:         'EEFFEEFF'
+        size:            4
+        offset:          348
+        align:           0
+        reloff:          0x00000000
+        nreloc:          0
+        flags:           0x00000000
+        reserved1:       0x00000000
+        reserved2:       0x00000000
+      - sectname:        __const
+        segname:         __TEXT
+        addr:            0x0000000000000008
+        content:         'EEFFEEFF'
+        size:            4
+        offset:          352
+        align:           0
+        reloff:          0x00000000
+        nreloc:          0
+        flags:           0x00000000
+        reserved1:       0x00000000
+        reserved2:       0x00000000

llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp

static Error addSection(StringRef SecName, StringRef Filename, Object &Obj) {
   // There's no segment named TargetSegName. Create a new load command and
   // Insert a new section into it.
   // TODO: 32-bit
   LoadCommand &NewSegment = Obj.addSegment(TargetSegName);
   NewSegment.Sections.push_back(Sec);
   return Error::success();
 }
 
+static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
+                               Object &Obj) {
+  for (LoadCommand &LC : Obj.LoadCommands)
+    for (Section &Sec : LC.Sections) {
+      if (Sec.CannonicalName == SecName) {
+        Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
+            FileOutputBuffer::create(Filename, Sec.Content.size());
+        if (!BufferOrErr)
+          return BufferOrErr.takeError();
+        std::unique_ptr<FileOutputBuffer> Buf = std::move(*BufferOrErr);
+        std::copy(Sec.Content.begin(), Sec.Content.end(),
+                  Buf->getBufferStart());
+        if (Error E = Buf->commit())
+          return E;
+        return Error::success();
+      }
+    }
+
+  return createStringError(object_error::parse_failed, "section '%s' not found",
+                           SecName.str().c_str());
+}
+
 static Error validateOptions(const CopyConfig &Config) {
   // TODO: Support section renaming in GNU objcopy for compatibility (see
   // http://lists.llvm.org/pipermail/llvm-dev/2019-May/132570.html).
 
   if (!Config.OnlySection.empty()) {
     for (const NameOrRegex &NR : Config.OnlySection)
       if (Error E = NR.isMachOCannonicalName())
         return E;
   }
 
   if (!Config.ToRemove.empty()) {
     for (const NameOrRegex &NR : Config.ToRemove)
       if (Error E = NR.isMachOCannonicalName())
         return E;
   }
 
   return Error::success();
 }
 
 static Error handleArgs(const CopyConfig &Config, Object &Obj) {
   if (Config.AllowBrokenLinks || !Config.BuildIdLinkDir.empty() ||
       Config.BuildIdLinkInput || Config.BuildIdLinkOutput ||
       !Config.SplitDWO.empty() || !Config.SymbolsPrefix.empty() ||
-      !Config.AllocSectionsPrefix.empty() || !Config.DumpSection.empty() ||
-      !Config.KeepSection.empty() || !Config.SymbolsToGlobalize.empty() ||
-      !Config.SymbolsToKeep.empty() || !Config.SymbolsToLocalize.empty() ||
-      !Config.SymbolsToWeaken.empty() || !Config.SymbolsToKeepGlobal.empty() ||
-      !Config.SectionsToRename.empty() || !Config.SymbolsToRename.empty() ||
+      !Config.AllocSectionsPrefix.empty() || !Config.KeepSection.empty() ||
+      !Config.SymbolsToGlobalize.empty() || !Config.SymbolsToKeep.empty() ||
+      !Config.SymbolsToLocalize.empty() || !Config.SymbolsToWeaken.empty() ||
+      !Config.SymbolsToKeepGlobal.empty() || !Config.SectionsToRename.empty() ||
+      !Config.SymbolsToRename.empty() ||
       !Config.UnneededSymbolsToRemove.empty() ||
       !Config.SetSectionFlags.empty() || Config.ExtractDWO ||
       Config.KeepFileSymbols || Config.LocalizeHidden || Config.PreserveDates ||
       Config.StripAllGNU || Config.StripDWO || Config.StripNonAlloc ||
       Config.StripSections || Config.Weaken || Config.DecompressDebugSections ||
       Config.StripDebug || Config.StripNonAlloc || Config.StripSections ||
       Config.StripUnneeded || Config.DiscardMode != DiscardType::None ||
       !Config.SymbolsToAdd.empty() || Config.EntryExpr) {
if (Error E = addSection(SecName, File, Obj))
       return E;
   }
 
   if (Config.StripAll)
     for (LoadCommand &LC : Obj.LoadCommands)
       for (Section &Sec : LC.Sections)
         Sec.Relocations.clear();
 
+  for (const auto &Flag : Config.DumpSection) {
+    std::pair<StringRef, StringRef> SecPair = Flag.split("=");
+    StringRef SecName = SecPair.first;
+    StringRef File = SecPair.second;
+    if (Error E = isValidMachOCannonicalName(SecName))
+      return E;
+    if (Error E = dumpSectionToFile(SecName, File, Obj))
+      return E;
+  }
+
   return Error::success();
 }
 
 Error writeOutput(Object &O, Buffer &Out, bool Is64Bit, bool IsLittleEndian) {
   // TODO: Support 16KB pages which are employed in iOS arm64 binaries:
   //       https://github.com/llvm/llvm-project/commit/1bebb2832ee312d3b0316dacff457a7a29435edb
   const uint64_t PageSize = 4096;