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

Reviewers: alexshap, rupprecht, jhenderson

Reviewed By: alexshap, rupprecht, jhenderson

Subscribers: MaskRay, jakehehrlich, abrachet, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66408

3 files changed, 128 insertions, 14 deletions

diff --git a/llvm/docs/CommandGuide/llvm-objcopy.rst b/llvm/docs/CommandGuide/llvm-objcopy.rst
index 689ebb7549f..0574a5e55f2 100644
--- a/llvm/docs/CommandGuide/llvm-objcopy.rst
+++ b/llvm/docs/CommandGuide/llvm-objcopy.rst
@@ -58,6 +58,18 @@ multiple file formats.
  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, ``<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
@@ -274,15 +286,6 @@ them.
 
  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.
diff --git a/llvm/test/tools/llvm-objcopy/MachO/dump-section.test b/llvm/test/tools/llvm-objcopy/MachO/dump-section.test
new file mode 100644
index 00000000000..9a1227cdbbd
--- /dev/null
+++ b/llvm/test/tools/llvm-objcopy/MachO/dump-section.test
@@ -0,0 +1,82 @@
+## Show that llvm-objcopy extracts section contents into files specified by
+## --dump-section.
+
+# RUN: yaml2obj %s -o %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: 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
diff --git a/llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp b/llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp
index 1f68fda2392..ef3973e51ae 100644
--- a/llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp
+++ b/llvm/tools/llvm-objcopy/MachO/MachOObjcopy.cpp
@@ -84,16 +84,37 @@ static LoadCommand buildRPathLoadCommand(StringRef Path) {
   return LC;
 }
 
+static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
+                               Object &Obj) {
+  for (LoadCommand &LC : Obj.LoadCommands)
+    for (Section &Sec : LC.Sections) {
+      if (Sec.CanonicalName == 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);
+        llvm::copy(Sec.Content, 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 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.AddSection.empty() ||
-      !Config.DumpSection.empty() || !Config.KeepSection.empty() ||
-      Config.NewSymbolVisibility || !Config.SymbolsToGlobalize.empty() ||
-      !Config.SymbolsToKeep.empty() || !Config.SymbolsToLocalize.empty() ||
-      !Config.SymbolsToWeaken.empty() || !Config.SymbolsToKeepGlobal.empty() ||
-      !Config.SectionsToRename.empty() ||
+      !Config.KeepSection.empty() || Config.NewSymbolVisibility ||
+      !Config.SymbolsToGlobalize.empty() || !Config.SymbolsToKeep.empty() ||
+      !Config.SymbolsToLocalize.empty() || !Config.SymbolsToWeaken.empty() ||
+      !Config.SymbolsToKeepGlobal.empty() || !Config.SectionsToRename.empty() ||
       !Config.UnneededSymbolsToRemove.empty() ||
       !Config.SetSectionAlignment.empty() || !Config.SetSectionFlags.empty() ||
       Config.ExtractDWO || Config.KeepFileSymbols || Config.LocalizeHidden ||
@@ -119,6 +140,14 @@ static Error handleArgs(const CopyConfig &Config, Object &Obj) {
       for (Section &Sec : LC.Sections)
         Sec.Relocations.clear();
 
+  for (const StringRef &Flag : Config.DumpSection) {
+    std::pair<StringRef, StringRef> SecPair = Flag.split("=");
+    StringRef SecName = SecPair.first;
+    StringRef File = SecPair.second;
+    if (Error E = dumpSectionToFile(SecName, File, Obj))
+      return E;
+  }
+
   for (StringRef RPath : Config.RPathToAdd) {
     for (LoadCommand &LC : Obj.LoadCommands) {
       if (LC.MachOLoadCommand.load_command_data.cmd == MachO::LC_RPATH &&