path: root/source/Plugins/ABI/SysV-hexagon/ABISysV_hexagon.cpp

//===-- ABISysV_hexagon.cpp --------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "ABISysV_hexagon.h"

#include "lldb/Core/ConstString.h"
#include "lldb/Core/DataExtractor.h"
#include "lldb/Core/Error.h"
#include "lldb/Core/Log.h"
#include "lldb/Core/Module.h"
#include "lldb/Core/PluginManager.h"
#include "lldb/Core/RegisterValue.h"
#include "lldb/Core/Value.h"
#include "lldb/Core/ValueObjectConstResult.h"
#include "lldb/Core/ValueObjectRegister.h"
#include "lldb/Core/ValueObjectMemory.h"
#include "lldb/Symbol/ClangASTContext.h"
#include "lldb/Symbol/UnwindPlan.h"
#include "lldb/Target/Target.h"
#include "lldb/Target/Process.h"
#include "lldb/Target/RegisterContext.h"
#include "lldb/Target/StackFrame.h"
#include "lldb/Target/Thread.h"

#include "llvm/ADT/Triple.h"

#include "llvm/IR/Type.h"

using namespace lldb;
using namespace lldb_private;

static RegisterInfo g_register_infos[] = 
{
    // hexagon-core.xml
    { "r00"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  0,  0, LLDB_INVALID_REGNUM,     0,  0 }, NULL, NULL },
    { "r01"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  1,  1, LLDB_INVALID_REGNUM,     1,  1 }, NULL, NULL },
    { "r02"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  2,  2, LLDB_INVALID_REGNUM,     2,  2 }, NULL, NULL },
    { "r03"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  3,  3, LLDB_INVALID_REGNUM,     3,  3 }, NULL, NULL },
    { "r04"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  4,  4, LLDB_INVALID_REGNUM,     4,  4 }, NULL, NULL },
    { "r05"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  5,  5, LLDB_INVALID_REGNUM,     5,  5 }, NULL, NULL },
    { "r06"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  6,  6, LLDB_INVALID_REGNUM,     6,  6 }, NULL, NULL },
    { "r07"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  7,  7, LLDB_INVALID_REGNUM,     7,  7 }, NULL, NULL },
    { "r08"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  8,  8, LLDB_INVALID_REGNUM,     8,  8 }, NULL, NULL },
    { "r09"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, {  9,  9, LLDB_INVALID_REGNUM,     9,  9 }, NULL, NULL },
    { "r10"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 10, 10, LLDB_INVALID_REGNUM,    10, 10 }, NULL, NULL },
    { "r11"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 11, 11, LLDB_INVALID_REGNUM,    11, 11 }, NULL, NULL },
    { "r12"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 12, 12, LLDB_INVALID_REGNUM,    12, 12 }, NULL, NULL },
    { "r13"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 13, 13, LLDB_INVALID_REGNUM,    13, 13 }, NULL, NULL },
    { "r14"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 14, 14, LLDB_INVALID_REGNUM,    14, 14 }, NULL, NULL },
    { "r15"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 15, 15, LLDB_INVALID_REGNUM,    15, 15 }, NULL, NULL },
    { "r16"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 16, 16, LLDB_INVALID_REGNUM,    16, 16 }, NULL, NULL },
    { "r17"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 17, 17, LLDB_INVALID_REGNUM,    17, 17 }, NULL, NULL },
    { "r18"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 18, 18, LLDB_INVALID_REGNUM,    18, 18 }, NULL, NULL },
    { "r19"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 19, 19, LLDB_INVALID_REGNUM,    19, 19 }, NULL, NULL },
    { "r20"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 20, 20, LLDB_INVALID_REGNUM,    20, 20 }, NULL, NULL },
    { "r21"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 21, 21, LLDB_INVALID_REGNUM,    21, 21 }, NULL, NULL },
    { "r22"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 22, 22, LLDB_INVALID_REGNUM,    22, 22 }, NULL, NULL },
    { "r23"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 23, 23, LLDB_INVALID_REGNUM,    23, 23 }, NULL, NULL },
    { "r24"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 24, 24, LLDB_INVALID_REGNUM,    24, 24 }, NULL, NULL },
    { "r25"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 25, 25, LLDB_INVALID_REGNUM,    25, 25 }, NULL, NULL },
    { "r26"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 26, 26, LLDB_INVALID_REGNUM,    26, 26 }, NULL, NULL },
    { "r27"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 27, 27, LLDB_INVALID_REGNUM,    27, 27 }, NULL, NULL },
    { "r28"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 28, 28, LLDB_INVALID_REGNUM,    28, 28 }, NULL, NULL },
    { "sp"  ,"r29", 4, 0, eEncodingUint, eFormatAddressInfo, { 29, 29, LLDB_REGNUM_GENERIC_SP, 29, 29 }, NULL, NULL },
    { "fp"  ,"r30", 4, 0, eEncodingUint, eFormatAddressInfo, { 30, 30, LLDB_REGNUM_GENERIC_FP, 30, 30 }, NULL, NULL },
    { "lr"  ,"r31", 4, 0, eEncodingUint, eFormatAddressInfo, { 31, 31, LLDB_REGNUM_GENERIC_RA, 31, 31 }, NULL, NULL },
    { "sa0"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 32, 32, LLDB_INVALID_REGNUM,    32, 32 }, NULL, NULL },
    { "lc0"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 33, 33, LLDB_INVALID_REGNUM,    33, 33 }, NULL, NULL },
    { "sa1"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 34, 34, LLDB_INVALID_REGNUM,    34, 34 }, NULL, NULL },
    { "lc1"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 35, 35, LLDB_INVALID_REGNUM,    35, 35 }, NULL, NULL },
    // --> hexagon-v4/5/55/56-sim.xml
    { "p3_0"  , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 36, 36, LLDB_INVALID_REGNUM,    36, 36 }, NULL, NULL },
// PADDING {
    { "p00"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 37, 37, LLDB_INVALID_REGNUM,    37, 37 }, NULL, NULL },
// }
    { "m0"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 38, 38, LLDB_INVALID_REGNUM,    38, 38 }, NULL, NULL },
    { "m1"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 39, 39, LLDB_INVALID_REGNUM,    39, 39 }, NULL, NULL },
    { "usr"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 40, 40, LLDB_INVALID_REGNUM,    40, 40 }, NULL, NULL },
    { "pc"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 41, 41, LLDB_REGNUM_GENERIC_PC, 41, 41 }, NULL, NULL },
    { "ugp"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 42, 42, LLDB_INVALID_REGNUM,    42, 42 }, NULL, NULL },
    { "gp"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 43, 43, LLDB_INVALID_REGNUM,    43, 43 }, NULL, NULL },
    { "cs0"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 44, 44, LLDB_INVALID_REGNUM,    44, 44 }, NULL, NULL },
    { "cs1"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 45, 45, LLDB_INVALID_REGNUM,    45, 45 }, NULL, NULL },
// PADDING {
    { "p01"   , "", 4, 0, eEncodingInvalid, eFormatInvalid,     { 46, 46, LLDB_INVALID_REGNUM,    46, 46 }, NULL, NULL },
    { "p02"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 47, 47, LLDB_INVALID_REGNUM,    47, 47 }, NULL, NULL },
    { "p03"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 48, 48, LLDB_INVALID_REGNUM,    48, 48 }, NULL, NULL },
    { "p04"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 49, 49, LLDB_INVALID_REGNUM,    49, 49 }, NULL, NULL },
    { "p05"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 50, 50, LLDB_INVALID_REGNUM,    50, 50 }, NULL, NULL },
    { "p06"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 51, 51, LLDB_INVALID_REGNUM,    51, 51 }, NULL, NULL },
    { "p07"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 52, 52, LLDB_INVALID_REGNUM,    52, 52 }, NULL, NULL },
    { "p08"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 53, 53, LLDB_INVALID_REGNUM,    53, 53 }, NULL, NULL },
    { "p09"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 54, 54, LLDB_INVALID_REGNUM,    54, 54 }, NULL, NULL },
    { "p10"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 55, 55, LLDB_INVALID_REGNUM,    55, 55 }, NULL, NULL },
    { "p11"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 56, 56, LLDB_INVALID_REGNUM,    56, 56 }, NULL, NULL },
    { "p12"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 57, 57, LLDB_INVALID_REGNUM,    57, 57 }, NULL, NULL },
    { "p13"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 58, 58, LLDB_INVALID_REGNUM,    58, 58 }, NULL, NULL },
    { "p14"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 59, 59, LLDB_INVALID_REGNUM,    59, 59 }, NULL, NULL },
    { "p15"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 60, 60, LLDB_INVALID_REGNUM,    60, 60 }, NULL, NULL },
    { "p16"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 61, 61, LLDB_INVALID_REGNUM,    61, 61 }, NULL, NULL },
    { "p17"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 62, 62, LLDB_INVALID_REGNUM,    62, 62 }, NULL, NULL },
    { "p18"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 63, 63, LLDB_INVALID_REGNUM,    63, 63 }, NULL, NULL },
// }
    { "sgp0"  , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 64, 64, LLDB_INVALID_REGNUM,    64, 64 }, NULL, NULL },
// PADDING {
    { "p19"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 65, 65, LLDB_INVALID_REGNUM,    65, 65 }, NULL, NULL },
// }
    { "stid"  , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 66, 66, LLDB_INVALID_REGNUM,    66, 66 }, NULL, NULL },
    { "elr"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 67, 67, LLDB_INVALID_REGNUM,    67, 67 }, NULL, NULL },
    { "badva0", "", 4, 0, eEncodingUint, eFormatAddressInfo, { 68, 68, LLDB_INVALID_REGNUM,    68, 68 }, NULL, NULL },
    { "badva1", "", 4, 0, eEncodingUint, eFormatAddressInfo, { 69, 69, LLDB_INVALID_REGNUM,    69, 69 }, NULL, NULL },
    { "ssr"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 70, 70, LLDB_INVALID_REGNUM,    70, 70 }, NULL, NULL },
    { "ccr"   , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 71, 71, LLDB_INVALID_REGNUM,    71, 71 }, NULL, NULL },
    { "htid"  , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 72, 72, LLDB_INVALID_REGNUM,    72, 72 }, NULL, NULL },
// PADDING {
    { "p20"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 73, 73, LLDB_INVALID_REGNUM,    73, 73 }, NULL, NULL },
// }
    { "imask" , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 74, 74, LLDB_INVALID_REGNUM,    74, 74 }, NULL, NULL },
// PADDING {
    { "p21"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 75, 75, LLDB_INVALID_REGNUM,    75, 75 }, NULL, NULL },
    { "p22"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 76, 76, LLDB_INVALID_REGNUM,    76, 76 }, NULL, NULL },
    { "p23"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 77, 77, LLDB_INVALID_REGNUM,    77, 77 }, NULL, NULL },
    { "p24"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 78, 78, LLDB_INVALID_REGNUM,    78, 78 }, NULL, NULL },
    { "p25"   , "", 4, 0, eEncodingInvalid, eFormatInvalid, { 79, 79, LLDB_INVALID_REGNUM,    79, 79 }, NULL, NULL },
 // }
    { "g0"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 80, 80, LLDB_INVALID_REGNUM,    80, 80 }, NULL, NULL },
    { "g1"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 81, 81, LLDB_INVALID_REGNUM,    81, 81 }, NULL, NULL },
    { "g2"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 82, 82, LLDB_INVALID_REGNUM,    82, 82 }, NULL, NULL },
    { "g3"    , "", 4, 0, eEncodingUint, eFormatAddressInfo, { 83, 83, LLDB_INVALID_REGNUM,    83, 83 }, NULL, NULL }
};

static const uint32_t k_num_register_infos = sizeof(g_register_infos)/sizeof(RegisterInfo);
static bool g_register_info_names_constified = false;

const lldb_private::RegisterInfo *
ABISysV_hexagon::GetRegisterInfoArray ( uint32_t &count )
{
    // Make the C-string names and alt_names for the register infos into const 
    // C-string values by having the ConstString unique the names in the global
    // constant C-string pool.
    if (!g_register_info_names_constified)
    {
        g_register_info_names_constified = true;
        for (uint32_t i=0; i<k_num_register_infos; ++i)
        {
            if (g_register_infos[i].name)
                g_register_infos[i].name = ConstString(g_register_infos[i].name).GetCString();
            if (g_register_infos[i].alt_name)
                g_register_infos[i].alt_name = ConstString(g_register_infos[i].alt_name).GetCString();
        }
    }
    count = k_num_register_infos;
    return g_register_infos;
}

/*
    http://en.wikipedia.org/wiki/Red_zone_%28computing%29

    In computing, a red zone is a fixed size area in memory beyond the stack pointer that has not been
    "allocated". This region of memory is not to be modified by interrupt/exception/signal handlers.
    This allows the space to be used for temporary data without the extra overhead of modifying the
    stack pointer. The x86-64 ABI mandates a 128 byte red zone.[1] The OpenRISC toolchain assumes a
    128 byte red zone though it is not documented.
*/
size_t
ABISysV_hexagon::GetRedZoneSize () const
{
    return 0;
}

//------------------------------------------------------------------
// Static Functions
//------------------------------------------------------------------
ABISP
ABISysV_hexagon::CreateInstance ( const ArchSpec &arch )
{
    static ABISP g_abi_sp;
    if (arch.GetTriple().getArch() == llvm::Triple::hexagon)
    {
        if (!g_abi_sp)
            g_abi_sp.reset (new ABISysV_hexagon);
        return g_abi_sp;
    }
    return ABISP();
}

bool
ABISysV_hexagon::PrepareTrivialCall ( Thread &thread, 
                                      lldb::addr_t  sp    , 
                                      lldb::addr_t  pc    , 
                                      lldb::addr_t  ra    , 
                                      llvm::ArrayRef<addr_t> args ) const
{
    // we don't use the traditional trivial call specialized for jit
    return false;
}

/*

// AD:
//  . safeguard the current stack
//  . how can we know that the called function will create its own frame properly?
//  . we could manually make a new stack first:
//      2. push RA
//      3. push FP
//      4. FP = SP
//      5. SP = SP ( since no locals in our temp frame )

// AD 6/05/2014
//  . variable argument list parameters are not passed via registers, they are passed on
//    the stack.  This presents us with a problem, since we need to know when the valist
//    starts.  Currently I can find out if a function is varg, but not how many
//    real parameters it takes.  Thus I don't know when to start spilling the vargs.  For
//    the time being, to progress, I will assume that it takes on real parameter before
//    the vargs list starts.

// AD 06/05/2014
//  . how do we adhere to the stack alignment requirements

// AD 06/05/2014
//  . handle 64bit values and their register / stack requirements

*/
#define HEX_ABI_DEBUG 1
bool
ABISysV_hexagon::PrepareTrivialCall ( Thread &thread, 
                                      lldb::addr_t  sp  , 
                                      lldb::addr_t  pc  , 
                                      lldb::addr_t  ra  , 
                                      llvm::Type   &prototype,
                                      llvm::ArrayRef<ABI::CallArgument> args) const
{
    // default number of register passed arguments for varg functions
    const int nVArgRegParams = 1;
    Error error;

    // grab the process so we have access to the memory for spilling
    lldb::ProcessSP proc = thread.GetProcess( );

    // push host data onto target
    for ( size_t i = 0; i < args.size( ); i++ )
    {
        const ABI::CallArgument &arg = args[i];
        // skip over target values
        if ( arg.type == ABI::CallArgument::TargetValue )
            continue;
        // round up to 8 byte multiple
        size_t argSize = ( arg.size | 0x7 ) + 1;

        // create space on the stack for this data
        sp -= argSize;

        // write this argument onto the stack of the host process
        proc.get( )->WriteMemory( sp, arg.data, arg.size, error );
        if ( error.Fail( ) )
            return false;

        // update the argument with the target pointer
        //XXX: This is a gross hack for getting around the const
        *((size_t*)(&arg.value)) = sp;
    }


#if HEX_ABI_DEBUG
    // print the original stack pointer
    printf( "sp : %04lx \n", sp );
#endif

    // make sure number of parameters matches prototype
    assert( prototype.getFunctionNumParams( ) == args.size( ) );

    // check if this is a variable argument function
    bool isVArg = prototype.isFunctionVarArg();

    // get the register context for modifying all of the registers
    RegisterContext *reg_ctx = thread.GetRegisterContext().get();
    if (!reg_ctx)
        return false;
    
    // number of arguments passed by register
    int nRegArgs = nVArgRegParams;
    if (! isVArg )
    {
        // number of arguments is limited by [R0 : R5] space
        nRegArgs = args.size( );
        if ( nRegArgs > 6 )
            nRegArgs = 6;
    }

    // pass arguments that are passed via registers
    for ( int i = 0; i < nRegArgs; i++ )
    {
        // get the parameter as a u32
        uint32_t param = (uint32_t)args[i].value;
        // write argument into register
        if (!reg_ctx->WriteRegisterFromUnsigned( i, param ))
            return false;
    }

    // number of arguments to spill onto stack
    int nSpillArgs = args.size( ) - nRegArgs;
    // make space on the stack for arguments
    sp -= 4 * nSpillArgs;
    // align stack on an 8 byte boundary
    if ( sp & 7 )
        sp -= 4;

    // arguments that are passed on the stack
    for ( size_t i = nRegArgs, offs=0; i < args.size( ); i++ )
    {
        // get the parameter as a u32
        uint32_t param = (uint32_t)args[i].value;
        // write argument to stack
        proc->WriteMemory( sp + offs, (void*)&param, sizeof( param ), error );
        if ( !error.Success( ) )
            return false;
        // 
        offs += 4;
    }

    // update registers with current function call state
    reg_ctx->WriteRegisterFromUnsigned ( 41, pc );
    reg_ctx->WriteRegisterFromUnsigned ( 31, ra );
    reg_ctx->WriteRegisterFromUnsigned ( 29, sp );
//  reg_ctx->WriteRegisterFromUnsigned ( FP ??? );

#if HEX_ABI_DEBUG
    // quick and dirty stack dumper for debugging
    for ( int i = -8; i < 8; i++ )
    {
        uint32_t data = 0;
        lldb::addr_t addr = sp + i * 4;
        proc->ReadMemory( addr, (void*)&data, sizeof( data ), error );
        printf( "\n0x%04lx 0x%08x ", addr, data );
        if ( i == 0 ) printf( "<<-- sp" );
    }
    printf( "\n" );
#endif 
    
    return true;
}

bool
ABISysV_hexagon::GetArgumentValues ( Thread &thread, ValueList &values ) const
{
    return false;
}

Error
ABISysV_hexagon::SetReturnValueObject ( lldb::StackFrameSP &frame_sp, lldb::ValueObjectSP &new_value_sp )
{
    Error error;
    return error;
}

ValueObjectSP
ABISysV_hexagon::GetReturnValueObjectSimple ( Thread &thread, ClangASTType &return_clang_type ) const
{
    ValueObjectSP return_valobj_sp;
    return return_valobj_sp;
}

ValueObjectSP
ABISysV_hexagon::GetReturnValueObjectImpl ( Thread &thread, ClangASTType &return_clang_type ) const
{
    ValueObjectSP return_valobj_sp;
    return return_valobj_sp;
}

// called when we are on the first instruction of a new function
// for hexagon the return address is in RA (R31)
bool
ABISysV_hexagon::CreateFunctionEntryUnwindPlan ( UnwindPlan &unwind_plan )
{
    unwind_plan.Clear();
    unwind_plan.SetRegisterKind(eRegisterKindGeneric);
    unwind_plan.SetReturnAddressRegister(LLDB_REGNUM_GENERIC_RA);
    
    UnwindPlan::RowSP row(new UnwindPlan::Row);

    // Our Call Frame Address is the stack pointer value
    row->SetCFARegister(LLDB_REGNUM_GENERIC_SP);
    row->SetCFAOffset(4);
    row->SetOffset(0);

    // The previous PC is in the LR
    row->SetRegisterLocationToRegister(LLDB_REGNUM_GENERIC_PC, LLDB_REGNUM_GENERIC_RA, true);
    unwind_plan.AppendRow(row);
    
    unwind_plan.SetSourceName("hexagon at-func-entry default");
    unwind_plan.SetSourcedFromCompiler(eLazyBoolNo);
    return true;
}

bool
ABISysV_hexagon::CreateDefaultUnwindPlan ( UnwindPlan &unwind_plan )
{
    unwind_plan.Clear();
    unwind_plan.SetRegisterKind(eRegisterKindGeneric);

    uint32_t fp_reg_num = LLDB_REGNUM_GENERIC_FP;
    uint32_t sp_reg_num = LLDB_REGNUM_GENERIC_SP;
    uint32_t pc_reg_num = LLDB_REGNUM_GENERIC_PC;

    UnwindPlan::RowSP row(new UnwindPlan::Row);

    row->SetCFARegister(LLDB_REGNUM_GENERIC_FP);
    row->SetCFAOffset(8);

    row->SetRegisterLocationToAtCFAPlusOffset(fp_reg_num,-8, true);
    row->SetRegisterLocationToAtCFAPlusOffset(pc_reg_num,-4, true);
    row->SetRegisterLocationToIsCFAPlusOffset(sp_reg_num, 0, true);

    unwind_plan.AppendRow(row);
    unwind_plan.SetSourceName("hexagon default unwind plan");
    unwind_plan.SetSourcedFromCompiler(eLazyBoolNo);
    unwind_plan.SetUnwindPlanValidAtAllInstructions(eLazyBoolNo);
    return true;
}

/*
    Register		Usage					Saved By

    R0  - R5		parameters(a)			-
    R6  - R15		Scratch(b)				Caller
    R16 - R27		Scratch					Callee
    R28				Scratch(b)				Caller
    R29 - R31		Stack Frames			Callee(c)
    P3:0			Processor State			Caller

    a = the caller can change parameter values
    b = R14 - R15 and R28 are used by the procedure linkage table
    c = R29 - R31 are saved and restored by allocframe() and deallocframe()
*/
bool
ABISysV_hexagon::RegisterIsVolatile ( const RegisterInfo *reg_info )
{
    return !RegisterIsCalleeSaved( reg_info );
}

bool
ABISysV_hexagon::RegisterIsCalleeSaved ( const RegisterInfo *reg_info )
{
    int reg = ((reg_info->byte_offset) / 4);

    bool save  = (reg >= 16) && (reg <= 27);
         save |= (reg >= 29) && (reg <= 32);

    return save;
}

void
ABISysV_hexagon::Initialize( void )
{
    PluginManager::RegisterPlugin
    (
        GetPluginNameStatic(), 
        "System V ABI for hexagon targets",
        CreateInstance
    );
}

void
ABISysV_hexagon::Terminate( void )
{
    PluginManager::UnregisterPlugin( CreateInstance );
}

lldb_private::ConstString
ABISysV_hexagon::GetPluginNameStatic()
{
    static ConstString g_name( "sysv-hexagon" );
    return g_name;
}

//------------------------------------------------------------------
// PluginInterface protocol
//------------------------------------------------------------------
lldb_private::ConstString
ABISysV_hexagon::GetPluginName( void )
{
    return GetPluginNameStatic();
}

uint32_t
ABISysV_hexagon::GetPluginVersion( void )
{
    return 1;
}

// get value object specialized to work with llvm IR types
lldb::ValueObjectSP
ABISysV_hexagon::GetReturnValueObjectImpl( lldb_private::Thread &thread, llvm::Type &retType ) const
{
    Value value;
    ValueObjectSP vObjSP;

    // get the current register context
    RegisterContext *reg_ctx = thread.GetRegisterContext().get();
    if (!reg_ctx)
        return vObjSP;

    // for now just pop R0 to find the return value
    const lldb_private::RegisterInfo *r0_info = reg_ctx->GetRegisterInfoAtIndex( 0 );
    if ( r0_info == nullptr )
        return vObjSP;
    
    // void return type
    if ( retType.isVoidTy( ) )
    {
        value.GetScalar( ) = 0;
    }
    // integer / pointer return type
    else
    if ( retType.isIntegerTy( ) || retType.isPointerTy( ) )
    {
        // read r0 register value
        lldb_private::RegisterValue r0_value;
        if ( !reg_ctx->ReadRegister( r0_info, r0_value ) )
            return vObjSP;

        // push r0 into value
        uint32_t r0_u32 = r0_value.GetAsUInt32( );

        // account for integer size
        if ( retType.isIntegerTy() && retType.isSized() )
        {
            uint64_t size = retType.getScalarSizeInBits( );
            uint64_t mask = ( 1ull << size ) - 1;
            // mask out higher order bits then the type we expect
            r0_u32 &= mask;
        }

        value.GetScalar( ) = r0_u32;
    }
    // unsupported return type
    else
        return vObjSP;

    // pack the value into a ValueObjectSP
    vObjSP = ValueObjectConstResult::Create
    (
        thread.GetStackFrameAtIndex(0).get(),
        value,
        ConstString("")
    );
    return vObjSP;
}