[yaml2obj][MachO] Don't fill dummy data for virtual sections

Summary:
Currently, MachOWriter::writeSectionData writes dummy data (0xdeadbeef) to fill section data areas in the file even if the section is a virtual one. Since virtual sections don't occupy any space in the file, writing dummy data could results the  "OS.tell() - fileStart <= Sec.offset" assertion failure.

This patch fixes the bug by simply not writing any dummy data for virtual sections.

Reviewers: beanz, jhenderson, rupprecht, alexshap

Reviewed By: alexshap

Subscribers: compnerd, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62991

llvm-svn: 363525

1 files changed, 15 insertions, 3 deletions

diff --git a/llvm/tools/yaml2obj/yaml2macho.cpp b/llvm/tools/yaml2obj/yaml2macho.cpp
index 2df03fd3901..9dcc7d1d759 100644
--- a/llvm/tools/yaml2obj/yaml2macho.cpp
+++ b/llvm/tools/yaml2obj/yaml2macho.cpp
@@ -262,6 +262,12 @@ Error MachOWriter::writeLoadCommands(raw_ostream &OS) {
   return Error::success();
 }
 
+static bool isVirtualSection(uint8_t type) {
+  return (type == MachO::S_ZEROFILL ||
+          type == MachO::S_GB_ZEROFILL ||
+          type == MachO::S_THREAD_LOCAL_ZEROFILL);
+}
+
 Error MachOWriter::writeSectionData(raw_ostream &OS) {
   bool FoundLinkEditSeg = false;
   for (auto &LC : Obj.LoadCommands) {
@@ -300,10 +306,16 @@ Error MachOWriter::writeSectionData(raw_ostream &OS) {
           } else if (0 == strncmp(&Sec.sectname[0], "__debug_line", 16)) {
             DWARFYAML::EmitDebugLine(OS, Obj.DWARF);
           }
-        } else {
-          // Fills section data with 0xDEADBEEF
-          Fill(OS, Sec.size, 0xDEADBEEFu);
+
+          continue;
         }
+
+        // Skip if it's a virtual section.
+        if (isVirtualSection(Sec.flags & MachO::SECTION_TYPE))
+          continue;
+
+        // Fill section data with 0xDEADBEEF
+        Fill(OS, Sec.size, 0xDEADBEEFu);
       }
       uint64_t segSize = is64Bit ? LC.Data.segment_command_64_data.filesize
                                  : LC.Data.segment_command_data.filesize;