[arm] Fix a double-register push operation.

src/arm/assembler-arm.cc

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // All Rights Reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions
 // are met:
 //
 // - Redistributions of source code must retain the above copyright notice,
 // this list of conditions and the following disclaimer.
 //
@@ skipping 284 matching lines @@
   shift_op_ = shift_op;
   rs_ = rs;
 }
 
 
 MemOperand::MemOperand(Register rn, int32_t offset, AddrMode am) {
   rn_ = rn;
   rm_ = no_reg;
   offset_ = offset;
   am_ = am;
+
+  // Accesses below the stack pointer are not safe, and are prohibited by the
+  // ABI. We can check obvious violations here.
+  if (rn.is(sp)) {
+    if (am == Offset) DCHECK_LE(0, offset);
+    if (am == NegOffset) DCHECK_GE(0, offset);
+  }
 }
 
 
 MemOperand::MemOperand(Register rn, Register rm, AddrMode am) {
   rn_ = rn;
   rm_ = rm;
   shift_op_ = LSL;
   shift_imm_ = 0;
   am_ = am;
 }
@@ skipping 3710 matching lines @@
     DCHECK(is_uint12(offset));
     instr_at_put(pc, SetLdrRegisterImmediateOffset(instr, offset));
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM