Fix big endian Power system linkage stack parameter alignment

On big endian Power, there was an issue with system linkage that was
causing parameters passed via the stack to be loaded incorrectly.
Specifically, the ABI specifies that the entire GPR's contents should be
saved on the stack, however the system linkage code was performing a
load of only the parameter size. While this works on little endian
systems, this causes the wrong bits of the argument to be loaded on big
endian systems.

This has been corrected by adjusting the stack offsets of parameters on
big endian systems so that the correct bytes of the full GPR contents
will be loaded. This should also correct #3525 on Power.

Fixes: #4765
Signed-off-by: Ben Thomas <ben@benthomas.ca>

compiler/p/codegen/OMRLinkage.cpp

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2019 IBM Corp. and others
+ * Copyright (c) 2000, 2020 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -166,7 +166,6 @@ TR::Instruction *OMR::Power::Linkage::saveArguments(TR::Instruction *cursor, boo
       TR::DataType type = paramCursor->getType();
       int32_t dtype = type.getDataType();
 
-
       // TODO: Is there an accurate assume to insert here ?
       if (lri >= 0)
          {
@@ -191,6 +190,9 @@ TR::Instruction *OMR::Power::Linkage::saveArguments(TR::Instruction *cursor, boo
                {
                case TR::Int8:
                case TR::Int16:
+                  if (properties.getSmallIntParmsAlignedRight())
+                     offset &= ~3;
+
                case TR::Int32:
                   op = TR::InstOpCode::stw;
                   length = 4;

compiler/p/codegen/OMRLinkage.hpp

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2019 IBM Corp. and others
+ * Copyright (c) 2000, 2020 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -68,11 +68,12 @@ class PPCMemoryArgument
 
 
 // linkage properties
-#define CallerCleanup       0x01
-#define RightToLeft         0x02
-#define IntegersInRegisters 0x04
-#define LongsInRegisters    0x08
-#define FloatsInRegisters   0x10
+#define CallerCleanup             0x01
+#define RightToLeft               0x02
+#define IntegersInRegisters       0x04
+#define LongsInRegisters          0x08
+#define FloatsInRegisters         0x10
+#define SmallIntParmsAlignedRight 0x20
 
 // register flags
 #define Preserved                   0x01
@@ -139,6 +140,8 @@ struct PPCLinkageProperties
 
    uint32_t getFloatsInRegisters() const {return (_properties & FloatsInRegisters);}
 
+   uint32_t getSmallIntParmsAlignedRight() const { return (_properties & SmallIntParmsAlignedRight); }
+
    uint32_t getRegisterFlags(TR::RealRegister::RegNum regNum) const
       {
       return _registerFlags[regNum];

compiler/p/codegen/PPCSystemLinkage.cpp

@@ -90,6 +90,9 @@ TR::PPCSystemLinkage::PPCSystemLinkage(TR::CodeGenerator *cg)
    {
    int i = 0;
    _properties._properties = IntegersInRegisters|FloatsInRegisters|RightToLeft;
+   if (comp()->target().cpu.isBigEndian())
+      _properties._properties |= SmallIntParmsAlignedRight;
+
    _properties._registerFlags[TR::RealRegister::NoReg] = 0;
    _properties._registerFlags[TR::RealRegister::gr0]   = 0;
    _properties._registerFlags[TR::RealRegister::gr1]   = Preserved|PPC_Reserved; // system sp
@@ -467,7 +470,11 @@ TR::PPCSystemLinkage::mapParameters(
    int32_t offset_from_top = 0;
    int32_t slot_size = sizeof(uintptrj_t);
 
-   bool saveParmsInLocalArea = comp()->target().bitness() == TR::endian_little && !hasParmsPassedOnStack(parmList);
+   // The 64-bit ELF V2 ABI Specification makes having a parameter save area optional if all parameters can be passed in
+   // registers. As a result, we cannot use the caller's parameter save area on 64-bit Linux if all parameters were
+   // passed in registers. However, we *must* use the caller's parameter save area if one or more parameters were passed
+   // on the stack to load those values correctly.
+   bool saveParmsInLocalArea = comp()->target().isLinux() && comp()->target().is64Bit() && !hasParmsPassedOnStack(parmList);
 
    if (linkage.getRightToLeft())
       {
@@ -477,6 +484,10 @@ TR::PPCSystemLinkage::mapParameters(
             parmCursor->setParameterOffset(offset_from_top + stackIndex);
          else
             parmCursor->setParameterOffset(offset_from_top + offsetToFirstParm + stackIndex);
+
+         if (linkage.getSmallIntParmsAlignedRight() && parmCursor->getType().isIntegral() && parmCursor->getSize() < slot_size)
+            parmCursor->setParameterOffset(parmCursor->getParameterOffset() + slot_size - parmCursor->getSize());
+
          offset_from_top += (parmCursor->getSize() + slot_size - 1) & (~(slot_size - 1));
          parmCursor = parameterIterator.getNext();
          }