[llvm-objdump] Print "..." instead of random data for virtual sections

When disassembling with -D, skip virtual sections by printing "..." for
each symbol.

This patch also implements `MachOObjectFile::isSectionVirtual`.

Test case comes from:

```
.zerofill __DATA,__common,_data64unsigned,472,3
```

Differential Revision: https://reviews.llvm.org/D45824

llvm-svn: 330342

4 files changed, 20 insertions, 2 deletions

diff --git a/llvm/lib/Object/MachOObjectFile.cpp b/llvm/lib/Object/MachOObjectFile.cpp
index adc54b42eba..ae5efc52055 100644
--- a/llvm/lib/Object/MachOObjectFile.cpp
+++ b/llvm/lib/Object/MachOObjectFile.cpp
@@ -1968,8 +1968,10 @@ unsigned MachOObjectFile::getSectionID(SectionRef Sec) const {
 }
 
 bool MachOObjectFile::isSectionVirtual(DataRefImpl Sec) const {
-  // FIXME: Unimplemented.
-  return false;
+  uint32_t Flags = getSectionFlags(*this, Sec);
+  unsigned SectionType = Flags & MachO::SECTION_TYPE;
+  return SectionType == MachO::S_ZEROFILL ||
+         SectionType == MachO::S_GB_ZEROFILL;
 }
 
 bool MachOObjectFile::isSectionBitcode(DataRefImpl Sec) const {
diff --git a/llvm/test/tools/llvm-objdump/AArch64/macho-zerofill.s b/llvm/test/tools/llvm-objdump/AArch64/macho-zerofill.s
new file mode 100644
index 00000000000..b790bb89f08
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/AArch64/macho-zerofill.s
@@ -0,0 +1,9 @@
+// RUN: llvm-mc < %s -triple aarch64-macho -filetype=obj | llvm-objdump -triple=aarch64-- -D - | FileCheck %s
+
+
+// Check that we don't print garbage when we dump zerofill sections.
+
+.zerofill __DATA,__common,_data64unsigned,472,3
+// CHECK: Disassembly of section __DATA,__common:
+// CHECK: ltmp1:
+// CHECK-NEXT: ...
diff --git a/llvm/test/tools/llvm-objdump/Inputs/zerofill.macho-x86_64.o b/llvm/test/tools/llvm-objdump/Inputs/zerofill.macho-x86_64.o
new file mode 100644
index 00000000000..272d7d5ccdf
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/Inputs/zerofill.macho-x86_64.o
diff --git a/llvm/tools/llvm-objdump/llvm-objdump.cpp b/llvm/tools/llvm-objdump/llvm-objdump.cpp
index 718d5749412..5bea3a7860b 100644
--- a/llvm/tools/llvm-objdump/llvm-objdump.cpp
+++ b/llvm/tools/llvm-objdump/llvm-objdump.cpp
@@ -1494,6 +1494,13 @@ static void DisassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
 
       outs() << '\n' << std::get<1>(Symbols[si]) << ":\n";
 
+      // Don't print raw contents of a virtual section. A virtual section
+      // doesn't have any contents in the file.
+      if (Section.isVirtual()) {
+        outs() << "...\n";
+        continue;
+      }
+
 #ifndef NDEBUG
       raw_ostream &DebugOut = DebugFlag ? dbgs() : nulls();
 #else