1 files changed, 47 insertions, 2 deletions
diff --git a/lib/MC/MCAssembler.cpp b/lib/MC/MCAssembler.cpp
index 2c698e7..96227db 100644
--- a/lib/MC/MCAssembler.cpp
+++ b/lib/MC/MCAssembler.cpp
@@ -1066,9 +1066,54 @@ void MCAssembler::LayoutSection(MCSectionData &SD) {
 ///
 /// FIXME this is X86 32-bit specific and should move to a better place.
 static uint64_t WriteNopData(uint64_t Count, MachObjectWriter &MOW) {
-  // FIXME for now just use the 0x90 nop opcode byte.
+  static const uint8_t Nops[16][16] = {
+    // nop
+    {0x90},
+    // xchg %ax,%ax
+    {0x66, 0x90},
+    // nopl (%[re]ax)
+    {0x0f, 0x1f, 0x00},
+    // nopl 0(%[re]ax)
+    {0x0f, 0x1f, 0x40, 0x00},
+    // nopl 0(%[re]ax,%[re]ax,1)
+    {0x0f, 0x1f, 0x44, 0x00, 0x00},
+    // nopw 0(%[re]ax,%[re]ax,1)
+    {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
+    // nopl 0L(%[re]ax)
+    {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
+    // nopl 0L(%[re]ax,%[re]ax,1)
+    {0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
+    // nopw 0L(%[re]ax,%[re]ax,1)
+    {0x66, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
+    // nopw %cs:0L(%[re]ax,%[re]ax,1)
+    {0x66, 0x2e, 0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00},
+    // nopl 0(%[re]ax,%[re]ax,1)
+    // nopw 0(%[re]ax,%[re]ax,1)
+    {0x0f, 0x1f, 0x44, 0x00, 0x00,
+     0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
+    // nopw 0(%[re]ax,%[re]ax,1)
+    // nopw 0(%[re]ax,%[re]ax,1)
+    {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
+     0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00},
+    // nopw 0(%[re]ax,%[re]ax,1)
+    // nopl 0L(%[re]ax) */
+    {0x66, 0x0f, 0x1f, 0x44, 0x00, 0x00,
+     0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
+    // nopl 0L(%[re]ax)
+    // nopl 0L(%[re]ax)
+    {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
+     0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00},
+    // nopl 0L(%[re]ax)
+    // nopl 0L(%[re]ax,%[re]ax,1)
+    {0x0f, 0x1f, 0x80, 0x00, 0x00, 0x00, 0x00,
+     0x0f, 0x1f, 0x84, 0x00, 0x00, 0x00, 0x00, 0x00}
+  };
+
+  if (Count > 15)
+    return 0;
+
   for (uint64_t i = 0; i < Count; i++)
-    MOW.Write8 (uint8_t(0x90));
+    MOW.Write8 (uint8_t(Nops[Count - 1][i]));
 
   return Count;
 }