[MC] Adjust StringTableBuilder for linked Mach-O binaries

LD64 emits string tables which start with a space and a zero byte.
This diff adjusts StringTableBuilder for linked Mach-O binaries to match LD64's behavior.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D89561

1 files changed, 14 insertions, 1 deletions

diff --git a/llvm/lib/MC/StringTableBuilder.cpp b/llvm/lib/MC/StringTableBuilder.cpp
index c9c88ec..973c590 100644
--- a/llvm/lib/MC/StringTableBuilder.cpp
+++ b/llvm/lib/MC/StringTableBuilder.cpp
@@ -33,7 +33,12 @@ void StringTableBuilder::initSize() {
   case DWARF:
     Size = 0;
     break;
+  case MachOLinked:
+  case MachO64Linked:
+    Size = 2;
+    break;
   case MachO:
+  case MachO64:
   case ELF:
     // Start the table with a NUL byte.
     Size = 1;
@@ -161,8 +166,16 @@ void StringTableBuilder::finalizeStringTable(bool Optimize) {
     }
   }
 
-  if (K == MachO)
+  if (K == MachO || K == MachOLinked)
     Size = alignTo(Size, 4); // Pad to multiple of 4.
+  if (K == MachO64 || K == MachO64Linked)
+    Size = alignTo(Size, 8); // Pad to multiple of 8.
+
+  // According to ld64 the string table of a final linked Mach-O binary starts
+  // with " ", i.e. the first byte is ' ' and the second byte is zero. In
+  // 'initSize()' we reserved the first two bytes for holding this string.
+  if (K == MachOLinked || K == MachO64Linked)
+    StringIndexMap[CachedHashStringRef(" ")] = 0;
 
   // The first byte in an ELF string table must be null, according to the ELF
   // specification. In 'initSize()' we reserved the first byte to hold null for