Change ARM exit frame layout and alingment handling...

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
===================================================================
--- src/arm/macro-assembler-arm.cc	(revision 6446)
+++ src/arm/macro-assembler-arm.cc	(working copy)
@@ -1,4 +1,4 @@
-// Copyright 2010 the V8 project authors. All rights reserved.
+// Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
@@ -615,37 +615,24 @@
 
 
 void MacroAssembler::EnterExitFrame(bool save_doubles) {
-  // r0 is argc.
-  // Compute callee's stack pointer before making changes and save it as
-  // ip register so that it is restored as sp register on exit, thereby
-  // popping the args.
+  // Compute the argv pointer in a callee-saved register.
+  add(r6, sp, Operand(r0, LSL, kPointerSizeLog2));
+  sub(r6, r6, Operand(kPointerSize));
 
-  // ip = sp + kPointerSize * #args;
-  add(ip, sp, Operand(r0, LSL, kPointerSizeLog2));
-
-  // Compute the argv pointer and keep it in a callee-saved register.
-  sub(r6, ip, Operand(kPointerSize));
-
-  // Prepare the stack to be aligned when calling into C. After this point there
-  // are 5 pushes before the call into C, so the stack needs to be aligned after
-  // 5 pushes.
-  int frame_alignment = ActivationFrameAlignment();
-  int frame_alignment_mask = frame_alignment - 1;
-  if (frame_alignment != kPointerSize) {
-    // The following code needs to be more general if this assert does not hold.
-    ASSERT(frame_alignment == 2 * kPointerSize);
-    // With 5 pushes left the frame must be unaligned at this point.
-    mov(r7, Operand(Smi::FromInt(0)));
-    tst(sp, Operand((frame_alignment - kPointerSize) & frame_alignment_mask));
-    push(r7, eq);  // Push if aligned to make it unaligned.
-  }
-
-  // Push in reverse order: caller_fp, sp_on_exit, and caller_pc.
-  stm(db_w, sp, fp.bit() | ip.bit() | lr.bit());
+  // Setup the frame structure on the stack.
+  ASSERT_EQ(2 * kPointerSize, ExitFrameConstants::kCallerSPDisplacement);
+  ASSERT_EQ(1 * kPointerSize, ExitFrameConstants::kCallerPCOffset);
+  ASSERT_EQ(0 * kPointerSize, ExitFrameConstants::kCallerFPOffset);
+  Push(lr, fp);
   mov(fp, Operand(sp));  // Setup new frame pointer.
-
+  // Reserve room for saved entry sp and code object.
+  sub(sp, sp, Operand(2 * kPointerSize));
+  if (FLAG_debug_code) {
+    mov(ip, Operand(0));
+    str(ip, MemOperand(fp, ExitFrameConstants::kSPOffset));
+  }
   mov(ip, Operand(CodeObject()));
-  push(ip);  // Accessed from ExitFrame::code_slot.
+  str(ip, MemOperand(fp, ExitFrameConstants::kCodeOffset));
 
   // Save the frame pointer and the context in top.
   mov(ip, Operand(ExternalReference(Top::k_c_entry_fp_address)));
@@ -659,25 +646,30 @@
 
   // Optionally save all double registers.
   if (save_doubles) {
-    // TODO(regis): Use vstrm instruction.
-    // The stack alignment code above made sp unaligned, so add space for one
-    // more double register and use aligned addresses.
-    ASSERT(kDoubleSize == frame_alignment);
-    // Mark the frame as containing doubles by pushing a non-valid return
-    // address, i.e. 0.
-    ASSERT(ExitFrameConstants::kMarkerOffset == -2 * kPointerSize);
-    mov(ip, Operand(0));  // Marker and alignment word.
-    push(ip);
-    int space = DwVfpRegister::kNumRegisters * kDoubleSize + kPointerSize;
-    sub(sp, sp, Operand(space));
+    sub(sp, sp, Operand(DwVfpRegister::kNumRegisters * kDoubleSize));
+    const int offset = -2 * kPointerSize;
     for (int i = 0; i < DwVfpRegister::kNumRegisters; i++) {
       DwVfpRegister reg = DwVfpRegister::from_code(i);
-      vstr(reg, sp, i * kDoubleSize + kPointerSize);
+      vstr(reg, fp, offset - ((i + 1) * kDoubleSize));
     }
-    // Note that d0 will be accessible at fp - 2*kPointerSize -
-    // DwVfpRegister::kNumRegisters * kDoubleSize, since the code slot and the
-    // alignment word were pushed after the fp.
+    // Note that d0 will be accessible at
+    //   fp - 2 * kPointerSize - DwVfpRegister::kNumRegisters * kDoubleSize,
+    // since the sp slot and code slot were pushed after the fp.
   }
+
+  // Reserve place for the return address and align the frame preparing for
+  // calling the runtime function.
+  const int frame_alignment = MacroAssembler::ActivationFrameAlignment();
+  sub(sp, sp, Operand(kPointerSize));
+  if (frame_alignment > 0) {
+    ASSERT(IsPowerOf2(frame_alignment));
+    and_(sp, sp, Operand(-frame_alignment));
+  }
+
+  // Set the exit frame sp value to point just before the return address
+  // location.
+  add(ip, sp, Operand(kPointerSize));
+  str(ip, MemOperand(fp, ExitFrameConstants::kSPOffset));
 }
 
 
@@ -715,12 +707,10 @@
 void MacroAssembler::LeaveExitFrame(bool save_doubles) {
   // Optionally restore all double registers.
   if (save_doubles) {
-    // TODO(regis): Use vldrm instruction.
     for (int i = 0; i < DwVfpRegister::kNumRegisters; i++) {
       DwVfpRegister reg = DwVfpRegister::from_code(i);
-      // Register d15 is just below the marker.
-      const int offset = ExitFrameConstants::kMarkerOffset;
-      vldr(reg, fp, (i - DwVfpRegister::kNumRegisters) * kDoubleSize + offset);
+      const int offset = -2 * kPointerSize;
+      vldr(reg, fp, offset - ((i + 1) * kDoubleSize));
     }
   }
 
@@ -736,9 +726,12 @@
   str(r3, MemOperand(ip));
 #endif
 
-  // Pop the arguments, restore registers, and return.
-  mov(sp, Operand(fp));  // respect ABI stack constraint
-  ldm(ia, sp, fp.bit() | sp.bit() | pc.bit());
+  // Tear down the exit frame, pop the arguments, and return. Callee-saved
+  // register r4 still holds argc.
+  mov(sp, Operand(fp));
+  ldm(ia_w, sp, fp.bit() | lr.bit());
+  add(sp, sp, Operand(r4, LSL, kPointerSizeLog2));
+  mov(pc, lr);
 }